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diff --git a/.venv/lib/python3.12/site-packages/sqlalchemy/orm/strategies.py b/.venv/lib/python3.12/site-packages/sqlalchemy/orm/strategies.py
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+# orm/strategies.py
+# Copyright (C) 2005-2025 the SQLAlchemy authors and contributors
+# <see AUTHORS file>
+#
+# This module is part of SQLAlchemy and is released under
+# the MIT License: https://www.opensource.org/licenses/mit-license.php
+# mypy: ignore-errors
+
+
+"""sqlalchemy.orm.interfaces.LoaderStrategy
+   implementations, and related MapperOptions."""
+
+from __future__ import annotations
+
+import collections
+import itertools
+from typing import Any
+from typing import Dict
+from typing import Optional
+from typing import Tuple
+from typing import TYPE_CHECKING
+from typing import Union
+
+from . import attributes
+from . import exc as orm_exc
+from . import interfaces
+from . import loading
+from . import path_registry
+from . import properties
+from . import query
+from . import relationships
+from . import unitofwork
+from . import util as orm_util
+from .base import _DEFER_FOR_STATE
+from .base import _RAISE_FOR_STATE
+from .base import _SET_DEFERRED_EXPIRED
+from .base import ATTR_WAS_SET
+from .base import LoaderCallableStatus
+from .base import PASSIVE_OFF
+from .base import PassiveFlag
+from .context import _column_descriptions
+from .context import ORMCompileState
+from .context import ORMSelectCompileState
+from .context import QueryContext
+from .interfaces import LoaderStrategy
+from .interfaces import StrategizedProperty
+from .session import _state_session
+from .state import InstanceState
+from .strategy_options import Load
+from .util import _none_only_set
+from .util import AliasedClass
+from .. import event
+from .. import exc as sa_exc
+from .. import inspect
+from .. import log
+from .. import sql
+from .. import util
+from ..sql import util as sql_util
+from ..sql import visitors
+from ..sql.selectable import LABEL_STYLE_TABLENAME_PLUS_COL
+from ..sql.selectable import Select
+from ..util.typing import Literal
+
+if TYPE_CHECKING:
+    from .mapper import Mapper
+    from .relationships import RelationshipProperty
+    from ..sql.elements import ColumnElement
+
+
+def _register_attribute(
+    prop,
+    mapper,
+    useobject,
+    compare_function=None,
+    typecallable=None,
+    callable_=None,
+    proxy_property=None,
+    active_history=False,
+    impl_class=None,
+    **kw,
+):
+    listen_hooks = []
+
+    uselist = useobject and prop.uselist
+
+    if useobject and prop.single_parent:
+        listen_hooks.append(single_parent_validator)
+
+    if prop.key in prop.parent.validators:
+        fn, opts = prop.parent.validators[prop.key]
+        listen_hooks.append(
+            lambda desc, prop: orm_util._validator_events(
+                desc, prop.key, fn, **opts
+            )
+        )
+
+    if useobject:
+        listen_hooks.append(unitofwork.track_cascade_events)
+
+    # need to assemble backref listeners
+    # after the singleparentvalidator, mapper validator
+    if useobject:
+        backref = prop.back_populates
+        if backref and prop._effective_sync_backref:
+            listen_hooks.append(
+                lambda desc, prop: attributes.backref_listeners(
+                    desc, backref, uselist
+                )
+            )
+
+    # a single MapperProperty is shared down a class inheritance
+    # hierarchy, so we set up attribute instrumentation and backref event
+    # for each mapper down the hierarchy.
+
+    # typically, "mapper" is the same as prop.parent, due to the way
+    # the configure_mappers() process runs, however this is not strongly
+    # enforced, and in the case of a second configure_mappers() run the
+    # mapper here might not be prop.parent; also, a subclass mapper may
+    # be called here before a superclass mapper.  That is, can't depend
+    # on mappers not already being set up so we have to check each one.
+
+    for m in mapper.self_and_descendants:
+        if prop is m._props.get(
+            prop.key
+        ) and not m.class_manager._attr_has_impl(prop.key):
+            desc = attributes.register_attribute_impl(
+                m.class_,
+                prop.key,
+                parent_token=prop,
+                uselist=uselist,
+                compare_function=compare_function,
+                useobject=useobject,
+                trackparent=useobject
+                and (
+                    prop.single_parent
+                    or prop.direction is interfaces.ONETOMANY
+                ),
+                typecallable=typecallable,
+                callable_=callable_,
+                active_history=active_history,
+                impl_class=impl_class,
+                send_modified_events=not useobject or not prop.viewonly,
+                doc=prop.doc,
+                **kw,
+            )
+
+            for hook in listen_hooks:
+                hook(desc, prop)
+
+
+@properties.ColumnProperty.strategy_for(instrument=False, deferred=False)
+class UninstrumentedColumnLoader(LoaderStrategy):
+    """Represent a non-instrumented MapperProperty.
+
+    The polymorphic_on argument of mapper() often results in this,
+    if the argument is against the with_polymorphic selectable.
+
+    """
+
+    __slots__ = ("columns",)
+
+    def __init__(self, parent, strategy_key):
+        super().__init__(parent, strategy_key)
+        self.columns = self.parent_property.columns
+
+    def setup_query(
+        self,
+        compile_state,
+        query_entity,
+        path,
+        loadopt,
+        adapter,
+        column_collection=None,
+        **kwargs,
+    ):
+        for c in self.columns:
+            if adapter:
+                c = adapter.columns[c]
+            compile_state._append_dedupe_col_collection(c, column_collection)
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        pass
+
+
+@log.class_logger
+@properties.ColumnProperty.strategy_for(instrument=True, deferred=False)
+class ColumnLoader(LoaderStrategy):
+    """Provide loading behavior for a :class:`.ColumnProperty`."""
+
+    __slots__ = "columns", "is_composite"
+
+    def __init__(self, parent, strategy_key):
+        super().__init__(parent, strategy_key)
+        self.columns = self.parent_property.columns
+        self.is_composite = hasattr(self.parent_property, "composite_class")
+
+    def setup_query(
+        self,
+        compile_state,
+        query_entity,
+        path,
+        loadopt,
+        adapter,
+        column_collection,
+        memoized_populators,
+        check_for_adapt=False,
+        **kwargs,
+    ):
+        for c in self.columns:
+            if adapter:
+                if check_for_adapt:
+                    c = adapter.adapt_check_present(c)
+                    if c is None:
+                        return
+                else:
+                    c = adapter.columns[c]
+
+            compile_state._append_dedupe_col_collection(c, column_collection)
+
+        fetch = self.columns[0]
+        if adapter:
+            fetch = adapter.columns[fetch]
+            if fetch is None:
+                # None happens here only for dml bulk_persistence cases
+                # when context.DMLReturningColFilter is used
+                return
+
+        memoized_populators[self.parent_property] = fetch
+
+    def init_class_attribute(self, mapper):
+        self.is_class_level = True
+        coltype = self.columns[0].type
+        # TODO: check all columns ?  check for foreign key as well?
+        active_history = (
+            self.parent_property.active_history
+            or self.columns[0].primary_key
+            or (
+                mapper.version_id_col is not None
+                and mapper._columntoproperty.get(mapper.version_id_col, None)
+                is self.parent_property
+            )
+        )
+
+        _register_attribute(
+            self.parent_property,
+            mapper,
+            useobject=False,
+            compare_function=coltype.compare_values,
+            active_history=active_history,
+        )
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        # look through list of columns represented here
+        # to see which, if any, is present in the row.
+
+        for col in self.columns:
+            if adapter:
+                col = adapter.columns[col]
+            getter = result._getter(col, False)
+            if getter:
+                populators["quick"].append((self.key, getter))
+                break
+        else:
+            populators["expire"].append((self.key, True))
+
+
+@log.class_logger
+@properties.ColumnProperty.strategy_for(query_expression=True)
+class ExpressionColumnLoader(ColumnLoader):
+    def __init__(self, parent, strategy_key):
+        super().__init__(parent, strategy_key)
+
+        # compare to the "default" expression that is mapped in
+        # the column.   If it's sql.null, we don't need to render
+        # unless an expr is passed in the options.
+        null = sql.null().label(None)
+        self._have_default_expression = any(
+            not c.compare(null) for c in self.parent_property.columns
+        )
+
+    def setup_query(
+        self,
+        compile_state,
+        query_entity,
+        path,
+        loadopt,
+        adapter,
+        column_collection,
+        memoized_populators,
+        **kwargs,
+    ):
+        columns = None
+        if loadopt and loadopt._extra_criteria:
+            columns = loadopt._extra_criteria
+
+        elif self._have_default_expression:
+            columns = self.parent_property.columns
+
+        if columns is None:
+            return
+
+        for c in columns:
+            if adapter:
+                c = adapter.columns[c]
+            compile_state._append_dedupe_col_collection(c, column_collection)
+
+        fetch = columns[0]
+        if adapter:
+            fetch = adapter.columns[fetch]
+            if fetch is None:
+                # None is not expected to be the result of any
+                # adapter implementation here, however there may be theoretical
+                # usages of returning() with context.DMLReturningColFilter
+                return
+
+        memoized_populators[self.parent_property] = fetch
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        # look through list of columns represented here
+        # to see which, if any, is present in the row.
+        if loadopt and loadopt._extra_criteria:
+            columns = loadopt._extra_criteria
+
+            for col in columns:
+                if adapter:
+                    col = adapter.columns[col]
+                getter = result._getter(col, False)
+                if getter:
+                    populators["quick"].append((self.key, getter))
+                    break
+            else:
+                populators["expire"].append((self.key, True))
+
+    def init_class_attribute(self, mapper):
+        self.is_class_level = True
+
+        _register_attribute(
+            self.parent_property,
+            mapper,
+            useobject=False,
+            compare_function=self.columns[0].type.compare_values,
+            accepts_scalar_loader=False,
+        )
+
+
+@log.class_logger
+@properties.ColumnProperty.strategy_for(deferred=True, instrument=True)
+@properties.ColumnProperty.strategy_for(
+    deferred=True, instrument=True, raiseload=True
+)
+@properties.ColumnProperty.strategy_for(do_nothing=True)
+class DeferredColumnLoader(LoaderStrategy):
+    """Provide loading behavior for a deferred :class:`.ColumnProperty`."""
+
+    __slots__ = "columns", "group", "raiseload"
+
+    def __init__(self, parent, strategy_key):
+        super().__init__(parent, strategy_key)
+        if hasattr(self.parent_property, "composite_class"):
+            raise NotImplementedError(
+                "Deferred loading for composite types not implemented yet"
+            )
+        self.raiseload = self.strategy_opts.get("raiseload", False)
+        self.columns = self.parent_property.columns
+        self.group = self.parent_property.group
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        # for a DeferredColumnLoader, this method is only used during a
+        # "row processor only" query; see test_deferred.py ->
+        # tests with "rowproc_only" in their name.  As of the 1.0 series,
+        # loading._instance_processor doesn't use a "row processing" function
+        # to populate columns, instead it uses data in the "populators"
+        # dictionary.  Normally, the DeferredColumnLoader.setup_query()
+        # sets up that data in the "memoized_populators" dictionary
+        # and "create_row_processor()" here is never invoked.
+
+        if (
+            context.refresh_state
+            and context.query._compile_options._only_load_props
+            and self.key in context.query._compile_options._only_load_props
+        ):
+            self.parent_property._get_strategy(
+                (("deferred", False), ("instrument", True))
+            ).create_row_processor(
+                context,
+                query_entity,
+                path,
+                loadopt,
+                mapper,
+                result,
+                adapter,
+                populators,
+            )
+
+        elif not self.is_class_level:
+            if self.raiseload:
+                set_deferred_for_local_state = (
+                    self.parent_property._raise_column_loader
+                )
+            else:
+                set_deferred_for_local_state = (
+                    self.parent_property._deferred_column_loader
+                )
+            populators["new"].append((self.key, set_deferred_for_local_state))
+        else:
+            populators["expire"].append((self.key, False))
+
+    def init_class_attribute(self, mapper):
+        self.is_class_level = True
+
+        _register_attribute(
+            self.parent_property,
+            mapper,
+            useobject=False,
+            compare_function=self.columns[0].type.compare_values,
+            callable_=self._load_for_state,
+            load_on_unexpire=False,
+        )
+
+    def setup_query(
+        self,
+        compile_state,
+        query_entity,
+        path,
+        loadopt,
+        adapter,
+        column_collection,
+        memoized_populators,
+        only_load_props=None,
+        **kw,
+    ):
+        if (
+            (
+                compile_state.compile_options._render_for_subquery
+                and self.parent_property._renders_in_subqueries
+            )
+            or (
+                loadopt
+                and set(self.columns).intersection(
+                    self.parent._should_undefer_in_wildcard
+                )
+            )
+            or (
+                loadopt
+                and self.group
+                and loadopt.local_opts.get(
+                    "undefer_group_%s" % self.group, False
+                )
+            )
+            or (only_load_props and self.key in only_load_props)
+        ):
+            self.parent_property._get_strategy(
+                (("deferred", False), ("instrument", True))
+            ).setup_query(
+                compile_state,
+                query_entity,
+                path,
+                loadopt,
+                adapter,
+                column_collection,
+                memoized_populators,
+                **kw,
+            )
+        elif self.is_class_level:
+            memoized_populators[self.parent_property] = _SET_DEFERRED_EXPIRED
+        elif not self.raiseload:
+            memoized_populators[self.parent_property] = _DEFER_FOR_STATE
+        else:
+            memoized_populators[self.parent_property] = _RAISE_FOR_STATE
+
+    def _load_for_state(self, state, passive):
+        if not state.key:
+            return LoaderCallableStatus.ATTR_EMPTY
+
+        if not passive & PassiveFlag.SQL_OK:
+            return LoaderCallableStatus.PASSIVE_NO_RESULT
+
+        localparent = state.manager.mapper
+
+        if self.group:
+            toload = [
+                p.key
+                for p in localparent.iterate_properties
+                if isinstance(p, StrategizedProperty)
+                and isinstance(p.strategy, DeferredColumnLoader)
+                and p.group == self.group
+            ]
+        else:
+            toload = [self.key]
+
+        # narrow the keys down to just those which have no history
+        group = [k for k in toload if k in state.unmodified]
+
+        session = _state_session(state)
+        if session is None:
+            raise orm_exc.DetachedInstanceError(
+                "Parent instance %s is not bound to a Session; "
+                "deferred load operation of attribute '%s' cannot proceed"
+                % (orm_util.state_str(state), self.key)
+            )
+
+        if self.raiseload:
+            self._invoke_raise_load(state, passive, "raise")
+
+        loading.load_scalar_attributes(
+            state.mapper, state, set(group), PASSIVE_OFF
+        )
+
+        return LoaderCallableStatus.ATTR_WAS_SET
+
+    def _invoke_raise_load(self, state, passive, lazy):
+        raise sa_exc.InvalidRequestError(
+            "'%s' is not available due to raiseload=True" % (self,)
+        )
+
+
+class LoadDeferredColumns:
+    """serializable loader object used by DeferredColumnLoader"""
+
+    def __init__(self, key: str, raiseload: bool = False):
+        self.key = key
+        self.raiseload = raiseload
+
+    def __call__(self, state, passive=attributes.PASSIVE_OFF):
+        key = self.key
+
+        localparent = state.manager.mapper
+        prop = localparent._props[key]
+        if self.raiseload:
+            strategy_key = (
+                ("deferred", True),
+                ("instrument", True),
+                ("raiseload", True),
+            )
+        else:
+            strategy_key = (("deferred", True), ("instrument", True))
+        strategy = prop._get_strategy(strategy_key)
+        return strategy._load_for_state(state, passive)
+
+
+class AbstractRelationshipLoader(LoaderStrategy):
+    """LoaderStratgies which deal with related objects."""
+
+    __slots__ = "mapper", "target", "uselist", "entity"
+
+    def __init__(self, parent, strategy_key):
+        super().__init__(parent, strategy_key)
+        self.mapper = self.parent_property.mapper
+        self.entity = self.parent_property.entity
+        self.target = self.parent_property.target
+        self.uselist = self.parent_property.uselist
+
+    def _immediateload_create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        return self.parent_property._get_strategy(
+            (("lazy", "immediate"),)
+        ).create_row_processor(
+            context,
+            query_entity,
+            path,
+            loadopt,
+            mapper,
+            result,
+            adapter,
+            populators,
+        )
+
+
+@log.class_logger
+@relationships.RelationshipProperty.strategy_for(do_nothing=True)
+class DoNothingLoader(LoaderStrategy):
+    """Relationship loader that makes no change to the object's state.
+
+    Compared to NoLoader, this loader does not initialize the
+    collection/attribute to empty/none; the usual default LazyLoader will
+    take effect.
+
+    """
+
+
+@log.class_logger
+@relationships.RelationshipProperty.strategy_for(lazy="noload")
+@relationships.RelationshipProperty.strategy_for(lazy=None)
+class NoLoader(AbstractRelationshipLoader):
+    """Provide loading behavior for a :class:`.Relationship`
+    with "lazy=None".
+
+    """
+
+    __slots__ = ()
+
+    def init_class_attribute(self, mapper):
+        self.is_class_level = True
+
+        _register_attribute(
+            self.parent_property,
+            mapper,
+            useobject=True,
+            typecallable=self.parent_property.collection_class,
+        )
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        def invoke_no_load(state, dict_, row):
+            if self.uselist:
+                attributes.init_state_collection(state, dict_, self.key)
+            else:
+                dict_[self.key] = None
+
+        populators["new"].append((self.key, invoke_no_load))
+
+
+@log.class_logger
+@relationships.RelationshipProperty.strategy_for(lazy=True)
+@relationships.RelationshipProperty.strategy_for(lazy="select")
+@relationships.RelationshipProperty.strategy_for(lazy="raise")
+@relationships.RelationshipProperty.strategy_for(lazy="raise_on_sql")
+@relationships.RelationshipProperty.strategy_for(lazy="baked_select")
+class LazyLoader(
+    AbstractRelationshipLoader, util.MemoizedSlots, log.Identified
+):
+    """Provide loading behavior for a :class:`.Relationship`
+    with "lazy=True", that is loads when first accessed.
+
+    """
+
+    __slots__ = (
+        "_lazywhere",
+        "_rev_lazywhere",
+        "_lazyload_reverse_option",
+        "_order_by",
+        "use_get",
+        "is_aliased_class",
+        "_bind_to_col",
+        "_equated_columns",
+        "_rev_bind_to_col",
+        "_rev_equated_columns",
+        "_simple_lazy_clause",
+        "_raise_always",
+        "_raise_on_sql",
+    )
+
+    _lazywhere: ColumnElement[bool]
+    _bind_to_col: Dict[str, ColumnElement[Any]]
+    _rev_lazywhere: ColumnElement[bool]
+    _rev_bind_to_col: Dict[str, ColumnElement[Any]]
+
+    parent_property: RelationshipProperty[Any]
+
+    def __init__(
+        self, parent: RelationshipProperty[Any], strategy_key: Tuple[Any, ...]
+    ):
+        super().__init__(parent, strategy_key)
+        self._raise_always = self.strategy_opts["lazy"] == "raise"
+        self._raise_on_sql = self.strategy_opts["lazy"] == "raise_on_sql"
+
+        self.is_aliased_class = inspect(self.entity).is_aliased_class
+
+        join_condition = self.parent_property._join_condition
+        (
+            self._lazywhere,
+            self._bind_to_col,
+            self._equated_columns,
+        ) = join_condition.create_lazy_clause()
+
+        (
+            self._rev_lazywhere,
+            self._rev_bind_to_col,
+            self._rev_equated_columns,
+        ) = join_condition.create_lazy_clause(reverse_direction=True)
+
+        if self.parent_property.order_by:
+            self._order_by = [
+                sql_util._deep_annotate(elem, {"_orm_adapt": True})
+                for elem in util.to_list(self.parent_property.order_by)
+            ]
+        else:
+            self._order_by = None
+
+        self.logger.info("%s lazy loading clause %s", self, self._lazywhere)
+
+        # determine if our "lazywhere" clause is the same as the mapper's
+        # get() clause.  then we can just use mapper.get()
+        #
+        # TODO: the "not self.uselist" can be taken out entirely; a m2o
+        # load that populates for a list (very unusual, but is possible with
+        # the API) can still set for "None" and the attribute system will
+        # populate as an empty list.
+        self.use_get = (
+            not self.is_aliased_class
+            and not self.uselist
+            and self.entity._get_clause[0].compare(
+                self._lazywhere,
+                use_proxies=True,
+                compare_keys=False,
+                equivalents=self.mapper._equivalent_columns,
+            )
+        )
+
+        if self.use_get:
+            for col in list(self._equated_columns):
+                if col in self.mapper._equivalent_columns:
+                    for c in self.mapper._equivalent_columns[col]:
+                        self._equated_columns[c] = self._equated_columns[col]
+
+            self.logger.info(
+                "%s will use Session.get() to optimize instance loads", self
+            )
+
+    def init_class_attribute(self, mapper):
+        self.is_class_level = True
+
+        _legacy_inactive_history_style = (
+            self.parent_property._legacy_inactive_history_style
+        )
+
+        if self.parent_property.active_history:
+            active_history = True
+            _deferred_history = False
+
+        elif (
+            self.parent_property.direction is not interfaces.MANYTOONE
+            or not self.use_get
+        ):
+            if _legacy_inactive_history_style:
+                active_history = True
+                _deferred_history = False
+            else:
+                active_history = False
+                _deferred_history = True
+        else:
+            active_history = _deferred_history = False
+
+        _register_attribute(
+            self.parent_property,
+            mapper,
+            useobject=True,
+            callable_=self._load_for_state,
+            typecallable=self.parent_property.collection_class,
+            active_history=active_history,
+            _deferred_history=_deferred_history,
+        )
+
+    def _memoized_attr__simple_lazy_clause(self):
+        lazywhere = sql_util._deep_annotate(
+            self._lazywhere, {"_orm_adapt": True}
+        )
+
+        criterion, bind_to_col = (lazywhere, self._bind_to_col)
+
+        params = []
+
+        def visit_bindparam(bindparam):
+            bindparam.unique = False
+
+        visitors.traverse(criterion, {}, {"bindparam": visit_bindparam})
+
+        def visit_bindparam(bindparam):
+            if bindparam._identifying_key in bind_to_col:
+                params.append(
+                    (
+                        bindparam.key,
+                        bind_to_col[bindparam._identifying_key],
+                        None,
+                    )
+                )
+            elif bindparam.callable is None:
+                params.append((bindparam.key, None, bindparam.value))
+
+        criterion = visitors.cloned_traverse(
+            criterion, {}, {"bindparam": visit_bindparam}
+        )
+
+        return criterion, params
+
+    def _generate_lazy_clause(self, state, passive):
+        criterion, param_keys = self._simple_lazy_clause
+
+        if state is None:
+            return sql_util.adapt_criterion_to_null(
+                criterion, [key for key, ident, value in param_keys]
+            )
+
+        mapper = self.parent_property.parent
+
+        o = state.obj()  # strong ref
+        dict_ = attributes.instance_dict(o)
+
+        if passive & PassiveFlag.INIT_OK:
+            passive ^= PassiveFlag.INIT_OK
+
+        params = {}
+        for key, ident, value in param_keys:
+            if ident is not None:
+                if passive and passive & PassiveFlag.LOAD_AGAINST_COMMITTED:
+                    value = mapper._get_committed_state_attr_by_column(
+                        state, dict_, ident, passive
+                    )
+                else:
+                    value = mapper._get_state_attr_by_column(
+                        state, dict_, ident, passive
+                    )
+
+            params[key] = value
+
+        return criterion, params
+
+    def _invoke_raise_load(self, state, passive, lazy):
+        raise sa_exc.InvalidRequestError(
+            "'%s' is not available due to lazy='%s'" % (self, lazy)
+        )
+
+    def _load_for_state(
+        self,
+        state,
+        passive,
+        loadopt=None,
+        extra_criteria=(),
+        extra_options=(),
+        alternate_effective_path=None,
+        execution_options=util.EMPTY_DICT,
+    ):
+        if not state.key and (
+            (
+                not self.parent_property.load_on_pending
+                and not state._load_pending
+            )
+            or not state.session_id
+        ):
+            return LoaderCallableStatus.ATTR_EMPTY
+
+        pending = not state.key
+        primary_key_identity = None
+
+        use_get = self.use_get and (not loadopt or not loadopt._extra_criteria)
+
+        if (not passive & PassiveFlag.SQL_OK and not use_get) or (
+            not passive & attributes.NON_PERSISTENT_OK and pending
+        ):
+            return LoaderCallableStatus.PASSIVE_NO_RESULT
+
+        if (
+            # we were given lazy="raise"
+            self._raise_always
+            # the no_raise history-related flag was not passed
+            and not passive & PassiveFlag.NO_RAISE
+            and (
+                # if we are use_get and related_object_ok is disabled,
+                # which means we are at most looking in the identity map
+                # for history purposes or otherwise returning
+                # PASSIVE_NO_RESULT, don't raise.  This is also a
+                # history-related flag
+                not use_get
+                or passive & PassiveFlag.RELATED_OBJECT_OK
+            )
+        ):
+            self._invoke_raise_load(state, passive, "raise")
+
+        session = _state_session(state)
+        if not session:
+            if passive & PassiveFlag.NO_RAISE:
+                return LoaderCallableStatus.PASSIVE_NO_RESULT
+
+            raise orm_exc.DetachedInstanceError(
+                "Parent instance %s is not bound to a Session; "
+                "lazy load operation of attribute '%s' cannot proceed"
+                % (orm_util.state_str(state), self.key)
+            )
+
+        # if we have a simple primary key load, check the
+        # identity map without generating a Query at all
+        if use_get:
+            primary_key_identity = self._get_ident_for_use_get(
+                session, state, passive
+            )
+            if LoaderCallableStatus.PASSIVE_NO_RESULT in primary_key_identity:
+                return LoaderCallableStatus.PASSIVE_NO_RESULT
+            elif LoaderCallableStatus.NEVER_SET in primary_key_identity:
+                return LoaderCallableStatus.NEVER_SET
+
+            # test for None alone in primary_key_identity based on
+            # allow_partial_pks preference.   PASSIVE_NO_RESULT and NEVER_SET
+            # have already been tested above
+            if not self.mapper.allow_partial_pks:
+                if _none_only_set.intersection(primary_key_identity):
+                    return None
+            else:
+                if _none_only_set.issuperset(primary_key_identity):
+                    return None
+
+            if (
+                self.key in state.dict
+                and not passive & PassiveFlag.DEFERRED_HISTORY_LOAD
+            ):
+                return LoaderCallableStatus.ATTR_WAS_SET
+
+            # look for this identity in the identity map.  Delegate to the
+            # Query class in use, as it may have special rules for how it
+            # does this, including how it decides what the correct
+            # identity_token would be for this identity.
+
+            instance = session._identity_lookup(
+                self.entity,
+                primary_key_identity,
+                passive=passive,
+                lazy_loaded_from=state,
+            )
+
+            if instance is not None:
+                if instance is LoaderCallableStatus.PASSIVE_CLASS_MISMATCH:
+                    return None
+                else:
+                    return instance
+            elif (
+                not passive & PassiveFlag.SQL_OK
+                or not passive & PassiveFlag.RELATED_OBJECT_OK
+            ):
+                return LoaderCallableStatus.PASSIVE_NO_RESULT
+
+        return self._emit_lazyload(
+            session,
+            state,
+            primary_key_identity,
+            passive,
+            loadopt,
+            extra_criteria,
+            extra_options,
+            alternate_effective_path,
+            execution_options,
+        )
+
+    def _get_ident_for_use_get(self, session, state, passive):
+        instance_mapper = state.manager.mapper
+
+        if passive & PassiveFlag.LOAD_AGAINST_COMMITTED:
+            get_attr = instance_mapper._get_committed_state_attr_by_column
+        else:
+            get_attr = instance_mapper._get_state_attr_by_column
+
+        dict_ = state.dict
+
+        return [
+            get_attr(state, dict_, self._equated_columns[pk], passive=passive)
+            for pk in self.mapper.primary_key
+        ]
+
+    @util.preload_module("sqlalchemy.orm.strategy_options")
+    def _emit_lazyload(
+        self,
+        session,
+        state,
+        primary_key_identity,
+        passive,
+        loadopt,
+        extra_criteria,
+        extra_options,
+        alternate_effective_path,
+        execution_options,
+    ):
+        strategy_options = util.preloaded.orm_strategy_options
+
+        clauseelement = self.entity.__clause_element__()
+        stmt = Select._create_raw_select(
+            _raw_columns=[clauseelement],
+            _propagate_attrs=clauseelement._propagate_attrs,
+            _label_style=LABEL_STYLE_TABLENAME_PLUS_COL,
+            _compile_options=ORMCompileState.default_compile_options,
+        )
+        load_options = QueryContext.default_load_options
+
+        load_options += {
+            "_invoke_all_eagers": False,
+            "_lazy_loaded_from": state,
+        }
+
+        if self.parent_property.secondary is not None:
+            stmt = stmt.select_from(
+                self.mapper, self.parent_property.secondary
+            )
+
+        pending = not state.key
+
+        # don't autoflush on pending
+        if pending or passive & attributes.NO_AUTOFLUSH:
+            stmt._execution_options = util.immutabledict({"autoflush": False})
+
+        use_get = self.use_get
+
+        if state.load_options or (loadopt and loadopt._extra_criteria):
+            if alternate_effective_path is None:
+                effective_path = state.load_path[self.parent_property]
+            else:
+                effective_path = alternate_effective_path[self.parent_property]
+
+            opts = state.load_options
+
+            if loadopt and loadopt._extra_criteria:
+                use_get = False
+                opts += (
+                    orm_util.LoaderCriteriaOption(self.entity, extra_criteria),
+                )
+
+            stmt._with_options = opts
+        elif alternate_effective_path is None:
+            # this path is used if there are not already any options
+            # in the query, but an event may want to add them
+            effective_path = state.mapper._path_registry[self.parent_property]
+        else:
+            # added by immediateloader
+            effective_path = alternate_effective_path[self.parent_property]
+
+        if extra_options:
+            stmt._with_options += extra_options
+
+        stmt._compile_options += {"_current_path": effective_path}
+
+        if use_get:
+            if self._raise_on_sql and not passive & PassiveFlag.NO_RAISE:
+                self._invoke_raise_load(state, passive, "raise_on_sql")
+
+            return loading.load_on_pk_identity(
+                session,
+                stmt,
+                primary_key_identity,
+                load_options=load_options,
+                execution_options=execution_options,
+            )
+
+        if self._order_by:
+            stmt._order_by_clauses = self._order_by
+
+        def _lazyload_reverse(compile_context):
+            for rev in self.parent_property._reverse_property:
+                # reverse props that are MANYTOONE are loading *this*
+                # object from get(), so don't need to eager out to those.
+                if (
+                    rev.direction is interfaces.MANYTOONE
+                    and rev._use_get
+                    and not isinstance(rev.strategy, LazyLoader)
+                ):
+                    strategy_options.Load._construct_for_existing_path(
+                        compile_context.compile_options._current_path[
+                            rev.parent
+                        ]
+                    ).lazyload(rev).process_compile_state(compile_context)
+
+        stmt._with_context_options += (
+            (_lazyload_reverse, self.parent_property),
+        )
+
+        lazy_clause, params = self._generate_lazy_clause(state, passive)
+
+        if execution_options:
+            execution_options = util.EMPTY_DICT.merge_with(
+                execution_options,
+                {
+                    "_sa_orm_load_options": load_options,
+                },
+            )
+        else:
+            execution_options = {
+                "_sa_orm_load_options": load_options,
+            }
+
+        if (
+            self.key in state.dict
+            and not passive & PassiveFlag.DEFERRED_HISTORY_LOAD
+        ):
+            return LoaderCallableStatus.ATTR_WAS_SET
+
+        if pending:
+            if util.has_intersection(orm_util._none_set, params.values()):
+                return None
+
+        elif util.has_intersection(orm_util._never_set, params.values()):
+            return None
+
+        if self._raise_on_sql and not passive & PassiveFlag.NO_RAISE:
+            self._invoke_raise_load(state, passive, "raise_on_sql")
+
+        stmt._where_criteria = (lazy_clause,)
+
+        result = session.execute(
+            stmt, params, execution_options=execution_options
+        )
+
+        result = result.unique().scalars().all()
+
+        if self.uselist:
+            return result
+        else:
+            l = len(result)
+            if l:
+                if l > 1:
+                    util.warn(
+                        "Multiple rows returned with "
+                        "uselist=False for lazily-loaded attribute '%s' "
+                        % self.parent_property
+                    )
+
+                return result[0]
+            else:
+                return None
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        key = self.key
+
+        if (
+            context.load_options._is_user_refresh
+            and context.query._compile_options._only_load_props
+            and self.key in context.query._compile_options._only_load_props
+        ):
+            return self._immediateload_create_row_processor(
+                context,
+                query_entity,
+                path,
+                loadopt,
+                mapper,
+                result,
+                adapter,
+                populators,
+            )
+
+        if not self.is_class_level or (loadopt and loadopt._extra_criteria):
+            # we are not the primary manager for this attribute
+            # on this class - set up a
+            # per-instance lazyloader, which will override the
+            # class-level behavior.
+            # this currently only happens when using a
+            # "lazyload" option on a "no load"
+            # attribute - "eager" attributes always have a
+            # class-level lazyloader installed.
+            set_lazy_callable = (
+                InstanceState._instance_level_callable_processor
+            )(
+                mapper.class_manager,
+                LoadLazyAttribute(
+                    key,
+                    self,
+                    loadopt,
+                    (
+                        loadopt._generate_extra_criteria(context)
+                        if loadopt._extra_criteria
+                        else None
+                    ),
+                ),
+                key,
+            )
+
+            populators["new"].append((self.key, set_lazy_callable))
+        elif context.populate_existing or mapper.always_refresh:
+
+            def reset_for_lazy_callable(state, dict_, row):
+                # we are the primary manager for this attribute on
+                # this class - reset its
+                # per-instance attribute state, so that the class-level
+                # lazy loader is
+                # executed when next referenced on this instance.
+                # this is needed in
+                # populate_existing() types of scenarios to reset
+                # any existing state.
+                state._reset(dict_, key)
+
+            populators["new"].append((self.key, reset_for_lazy_callable))
+
+
+class LoadLazyAttribute:
+    """semi-serializable loader object used by LazyLoader
+
+    Historically, this object would be carried along with instances that
+    needed to run lazyloaders, so it had to be serializable to support
+    cached instances.
+
+    this is no longer a general requirement, and the case where this object
+    is used is exactly the case where we can't really serialize easily,
+    which is when extra criteria in the loader option is present.
+
+    We can't reliably serialize that as it refers to mapped entities and
+    AliasedClass objects that are local to the current process, which would
+    need to be matched up on deserialize e.g. the sqlalchemy.ext.serializer
+    approach.
+
+    """
+
+    def __init__(self, key, initiating_strategy, loadopt, extra_criteria):
+        self.key = key
+        self.strategy_key = initiating_strategy.strategy_key
+        self.loadopt = loadopt
+        self.extra_criteria = extra_criteria
+
+    def __getstate__(self):
+        if self.extra_criteria is not None:
+            util.warn(
+                "Can't reliably serialize a lazyload() option that "
+                "contains additional criteria; please use eager loading "
+                "for this case"
+            )
+        return {
+            "key": self.key,
+            "strategy_key": self.strategy_key,
+            "loadopt": self.loadopt,
+            "extra_criteria": (),
+        }
+
+    def __call__(self, state, passive=attributes.PASSIVE_OFF):
+        key = self.key
+        instance_mapper = state.manager.mapper
+        prop = instance_mapper._props[key]
+        strategy = prop._strategies[self.strategy_key]
+
+        return strategy._load_for_state(
+            state,
+            passive,
+            loadopt=self.loadopt,
+            extra_criteria=self.extra_criteria,
+        )
+
+
+class PostLoader(AbstractRelationshipLoader):
+    """A relationship loader that emits a second SELECT statement."""
+
+    __slots__ = ()
+
+    def _setup_for_recursion(self, context, path, loadopt, join_depth=None):
+        effective_path = (
+            context.compile_state.current_path or orm_util.PathRegistry.root
+        ) + path
+
+        top_level_context = context._get_top_level_context()
+        execution_options = util.immutabledict(
+            {"sa_top_level_orm_context": top_level_context}
+        )
+
+        if loadopt:
+            recursion_depth = loadopt.local_opts.get("recursion_depth", None)
+            unlimited_recursion = recursion_depth == -1
+        else:
+            recursion_depth = None
+            unlimited_recursion = False
+
+        if recursion_depth is not None:
+            if not self.parent_property._is_self_referential:
+                raise sa_exc.InvalidRequestError(
+                    f"recursion_depth option on relationship "
+                    f"{self.parent_property} not valid for "
+                    "non-self-referential relationship"
+                )
+            recursion_depth = context.execution_options.get(
+                f"_recursion_depth_{id(self)}", recursion_depth
+            )
+
+            if not unlimited_recursion and recursion_depth < 0:
+                return (
+                    effective_path,
+                    False,
+                    execution_options,
+                    recursion_depth,
+                )
+
+            if not unlimited_recursion:
+                execution_options = execution_options.union(
+                    {
+                        f"_recursion_depth_{id(self)}": recursion_depth - 1,
+                    }
+                )
+
+        if loading.PostLoad.path_exists(
+            context, effective_path, self.parent_property
+        ):
+            return effective_path, False, execution_options, recursion_depth
+
+        path_w_prop = path[self.parent_property]
+        effective_path_w_prop = effective_path[self.parent_property]
+
+        if not path_w_prop.contains(context.attributes, "loader"):
+            if join_depth:
+                if effective_path_w_prop.length / 2 > join_depth:
+                    return (
+                        effective_path,
+                        False,
+                        execution_options,
+                        recursion_depth,
+                    )
+            elif effective_path_w_prop.contains_mapper(self.mapper):
+                return (
+                    effective_path,
+                    False,
+                    execution_options,
+                    recursion_depth,
+                )
+
+        return effective_path, True, execution_options, recursion_depth
+
+
+@relationships.RelationshipProperty.strategy_for(lazy="immediate")
+class ImmediateLoader(PostLoader):
+    __slots__ = ("join_depth",)
+
+    def __init__(self, parent, strategy_key):
+        super().__init__(parent, strategy_key)
+        self.join_depth = self.parent_property.join_depth
+
+    def init_class_attribute(self, mapper):
+        self.parent_property._get_strategy(
+            (("lazy", "select"),)
+        ).init_class_attribute(mapper)
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        if not context.compile_state.compile_options._enable_eagerloads:
+            return
+
+        (
+            effective_path,
+            run_loader,
+            execution_options,
+            recursion_depth,
+        ) = self._setup_for_recursion(context, path, loadopt, self.join_depth)
+
+        if not run_loader:
+            # this will not emit SQL and will only emit for a many-to-one
+            # "use get" load.   the "_RELATED" part means it may return
+            # instance even if its expired, since this is a mutually-recursive
+            # load operation.
+            flags = attributes.PASSIVE_NO_FETCH_RELATED | PassiveFlag.NO_RAISE
+        else:
+            flags = attributes.PASSIVE_OFF | PassiveFlag.NO_RAISE
+
+        loading.PostLoad.callable_for_path(
+            context,
+            effective_path,
+            self.parent,
+            self.parent_property,
+            self._load_for_path,
+            loadopt,
+            flags,
+            recursion_depth,
+            execution_options,
+        )
+
+    def _load_for_path(
+        self,
+        context,
+        path,
+        states,
+        load_only,
+        loadopt,
+        flags,
+        recursion_depth,
+        execution_options,
+    ):
+        if recursion_depth:
+            new_opt = Load(loadopt.path.entity)
+            new_opt.context = (
+                loadopt,
+                loadopt._recurse(),
+            )
+            alternate_effective_path = path._truncate_recursive()
+            extra_options = (new_opt,)
+        else:
+            new_opt = None
+            alternate_effective_path = path
+            extra_options = ()
+
+        key = self.key
+        lazyloader = self.parent_property._get_strategy((("lazy", "select"),))
+        for state, overwrite in states:
+            dict_ = state.dict
+
+            if overwrite or key not in dict_:
+                value = lazyloader._load_for_state(
+                    state,
+                    flags,
+                    extra_options=extra_options,
+                    alternate_effective_path=alternate_effective_path,
+                    execution_options=execution_options,
+                )
+                if value not in (
+                    ATTR_WAS_SET,
+                    LoaderCallableStatus.PASSIVE_NO_RESULT,
+                ):
+                    state.get_impl(key).set_committed_value(
+                        state, dict_, value
+                    )
+
+
+@log.class_logger
+@relationships.RelationshipProperty.strategy_for(lazy="subquery")
+class SubqueryLoader(PostLoader):
+    __slots__ = ("join_depth",)
+
+    def __init__(self, parent, strategy_key):
+        super().__init__(parent, strategy_key)
+        self.join_depth = self.parent_property.join_depth
+
+    def init_class_attribute(self, mapper):
+        self.parent_property._get_strategy(
+            (("lazy", "select"),)
+        ).init_class_attribute(mapper)
+
+    def _get_leftmost(
+        self,
+        orig_query_entity_index,
+        subq_path,
+        current_compile_state,
+        is_root,
+    ):
+        given_subq_path = subq_path
+        subq_path = subq_path.path
+        subq_mapper = orm_util._class_to_mapper(subq_path[0])
+
+        # determine attributes of the leftmost mapper
+        if (
+            self.parent.isa(subq_mapper)
+            and self.parent_property is subq_path[1]
+        ):
+            leftmost_mapper, leftmost_prop = self.parent, self.parent_property
+        else:
+            leftmost_mapper, leftmost_prop = subq_mapper, subq_path[1]
+
+        if is_root:
+            # the subq_path is also coming from cached state, so when we start
+            # building up this path, it has to also be converted to be in terms
+            # of the current state. this is for the specific case of the entity
+            # is an AliasedClass against a subquery that's not otherwise going
+            # to adapt
+            new_subq_path = current_compile_state._entities[
+                orig_query_entity_index
+            ].entity_zero._path_registry[leftmost_prop]
+            additional = len(subq_path) - len(new_subq_path)
+            if additional:
+                new_subq_path += path_registry.PathRegistry.coerce(
+                    subq_path[-additional:]
+                )
+        else:
+            new_subq_path = given_subq_path
+
+        leftmost_cols = leftmost_prop.local_columns
+
+        leftmost_attr = [
+            getattr(
+                new_subq_path.path[0].entity,
+                leftmost_mapper._columntoproperty[c].key,
+            )
+            for c in leftmost_cols
+        ]
+
+        return leftmost_mapper, leftmost_attr, leftmost_prop, new_subq_path
+
+    def _generate_from_original_query(
+        self,
+        orig_compile_state,
+        orig_query,
+        leftmost_mapper,
+        leftmost_attr,
+        leftmost_relationship,
+        orig_entity,
+    ):
+        # reformat the original query
+        # to look only for significant columns
+        q = orig_query._clone().correlate(None)
+
+        # LEGACY: make a Query back from the select() !!
+        # This suits at least two legacy cases:
+        # 1. applications which expect before_compile() to be called
+        #    below when we run .subquery() on this query (Keystone)
+        # 2. applications which are doing subqueryload with complex
+        #    from_self() queries, as query.subquery() / .statement
+        #    has to do the full compile context for multiply-nested
+        #    from_self() (Neutron) - see test_subqload_from_self
+        #    for demo.
+        q2 = query.Query.__new__(query.Query)
+        q2.__dict__.update(q.__dict__)
+        q = q2
+
+        # set the query's "FROM" list explicitly to what the
+        # FROM list would be in any case, as we will be limiting
+        # the columns in the SELECT list which may no longer include
+        # all entities mentioned in things like WHERE, JOIN, etc.
+        if not q._from_obj:
+            q._enable_assertions = False
+            q.select_from.non_generative(
+                q,
+                *{
+                    ent["entity"]
+                    for ent in _column_descriptions(
+                        orig_query, compile_state=orig_compile_state
+                    )
+                    if ent["entity"] is not None
+                },
+            )
+
+        # select from the identity columns of the outer (specifically, these
+        # are the 'local_cols' of the property).  This will remove other
+        # columns from the query that might suggest the right entity which is
+        # why we do set select_from above.   The attributes we have are
+        # coerced and adapted using the original query's adapter, which is
+        # needed only for the case of adapting a subclass column to
+        # that of a polymorphic selectable, e.g. we have
+        # Engineer.primary_language and the entity is Person.  All other
+        # adaptations, e.g. from_self, select_entity_from(), will occur
+        # within the new query when it compiles, as the compile_state we are
+        # using here is only a partial one.  If the subqueryload is from a
+        # with_polymorphic() or other aliased() object, left_attr will already
+        # be the correct attributes so no adaptation is needed.
+        target_cols = orig_compile_state._adapt_col_list(
+            [
+                sql.coercions.expect(sql.roles.ColumnsClauseRole, o)
+                for o in leftmost_attr
+            ],
+            orig_compile_state._get_current_adapter(),
+        )
+        q._raw_columns = target_cols
+
+        distinct_target_key = leftmost_relationship.distinct_target_key
+
+        if distinct_target_key is True:
+            q._distinct = True
+        elif distinct_target_key is None:
+            # if target_cols refer to a non-primary key or only
+            # part of a composite primary key, set the q as distinct
+            for t in {c.table for c in target_cols}:
+                if not set(target_cols).issuperset(t.primary_key):
+                    q._distinct = True
+                    break
+
+        # don't need ORDER BY if no limit/offset
+        if not q._has_row_limiting_clause:
+            q._order_by_clauses = ()
+
+        if q._distinct is True and q._order_by_clauses:
+            # the logic to automatically add the order by columns to the query
+            # when distinct is True is deprecated in the query
+            to_add = sql_util.expand_column_list_from_order_by(
+                target_cols, q._order_by_clauses
+            )
+            if to_add:
+                q._set_entities(target_cols + to_add)
+
+        # the original query now becomes a subquery
+        # which we'll join onto.
+        # LEGACY: as "q" is a Query, the before_compile() event is invoked
+        # here.
+        embed_q = q.set_label_style(LABEL_STYLE_TABLENAME_PLUS_COL).subquery()
+        left_alias = orm_util.AliasedClass(
+            leftmost_mapper, embed_q, use_mapper_path=True
+        )
+        return left_alias
+
+    def _prep_for_joins(self, left_alias, subq_path):
+        # figure out what's being joined.  a.k.a. the fun part
+        to_join = []
+        pairs = list(subq_path.pairs())
+
+        for i, (mapper, prop) in enumerate(pairs):
+            if i > 0:
+                # look at the previous mapper in the chain -
+                # if it is as or more specific than this prop's
+                # mapper, use that instead.
+                # note we have an assumption here that
+                # the non-first element is always going to be a mapper,
+                # not an AliasedClass
+
+                prev_mapper = pairs[i - 1][1].mapper
+                to_append = prev_mapper if prev_mapper.isa(mapper) else mapper
+            else:
+                to_append = mapper
+
+            to_join.append((to_append, prop.key))
+
+        # determine the immediate parent class we are joining from,
+        # which needs to be aliased.
+
+        if len(to_join) < 2:
+            # in the case of a one level eager load, this is the
+            # leftmost "left_alias".
+            parent_alias = left_alias
+        else:
+            info = inspect(to_join[-1][0])
+            if info.is_aliased_class:
+                parent_alias = info.entity
+            else:
+                # alias a plain mapper as we may be
+                # joining multiple times
+                parent_alias = orm_util.AliasedClass(
+                    info.entity, use_mapper_path=True
+                )
+
+        local_cols = self.parent_property.local_columns
+
+        local_attr = [
+            getattr(parent_alias, self.parent._columntoproperty[c].key)
+            for c in local_cols
+        ]
+        return to_join, local_attr, parent_alias
+
+    def _apply_joins(
+        self, q, to_join, left_alias, parent_alias, effective_entity
+    ):
+        ltj = len(to_join)
+        if ltj == 1:
+            to_join = [
+                getattr(left_alias, to_join[0][1]).of_type(effective_entity)
+            ]
+        elif ltj == 2:
+            to_join = [
+                getattr(left_alias, to_join[0][1]).of_type(parent_alias),
+                getattr(parent_alias, to_join[-1][1]).of_type(
+                    effective_entity
+                ),
+            ]
+        elif ltj > 2:
+            middle = [
+                (
+                    (
+                        orm_util.AliasedClass(item[0])
+                        if not inspect(item[0]).is_aliased_class
+                        else item[0].entity
+                    ),
+                    item[1],
+                )
+                for item in to_join[1:-1]
+            ]
+            inner = []
+
+            while middle:
+                item = middle.pop(0)
+                attr = getattr(item[0], item[1])
+                if middle:
+                    attr = attr.of_type(middle[0][0])
+                else:
+                    attr = attr.of_type(parent_alias)
+
+                inner.append(attr)
+
+            to_join = (
+                [getattr(left_alias, to_join[0][1]).of_type(inner[0].parent)]
+                + inner
+                + [
+                    getattr(parent_alias, to_join[-1][1]).of_type(
+                        effective_entity
+                    )
+                ]
+            )
+
+        for attr in to_join:
+            q = q.join(attr)
+
+        return q
+
+    def _setup_options(
+        self,
+        context,
+        q,
+        subq_path,
+        rewritten_path,
+        orig_query,
+        effective_entity,
+        loadopt,
+    ):
+        # note that because the subqueryload object
+        # does not re-use the cached query, instead always making
+        # use of the current invoked query, while we have two queries
+        # here (orig and context.query), they are both non-cached
+        # queries and we can transfer the options as is without
+        # adjusting for new criteria.   Some work on #6881 / #6889
+        # brought this into question.
+        new_options = orig_query._with_options
+
+        if loadopt and loadopt._extra_criteria:
+            new_options += (
+                orm_util.LoaderCriteriaOption(
+                    self.entity,
+                    loadopt._generate_extra_criteria(context),
+                ),
+            )
+
+        # propagate loader options etc. to the new query.
+        # these will fire relative to subq_path.
+        q = q._with_current_path(rewritten_path)
+        q = q.options(*new_options)
+
+        return q
+
+    def _setup_outermost_orderby(self, q):
+        if self.parent_property.order_by:
+
+            def _setup_outermost_orderby(compile_context):
+                compile_context.eager_order_by += tuple(
+                    util.to_list(self.parent_property.order_by)
+                )
+
+            q = q._add_context_option(
+                _setup_outermost_orderby, self.parent_property
+            )
+
+        return q
+
+    class _SubqCollections:
+        """Given a :class:`_query.Query` used to emit the "subquery load",
+        provide a load interface that executes the query at the
+        first moment a value is needed.
+
+        """
+
+        __slots__ = (
+            "session",
+            "execution_options",
+            "load_options",
+            "params",
+            "subq",
+            "_data",
+        )
+
+        def __init__(self, context, subq):
+            # avoid creating a cycle by storing context
+            # even though that's preferable
+            self.session = context.session
+            self.execution_options = context.execution_options
+            self.load_options = context.load_options
+            self.params = context.params or {}
+            self.subq = subq
+            self._data = None
+
+        def get(self, key, default):
+            if self._data is None:
+                self._load()
+            return self._data.get(key, default)
+
+        def _load(self):
+            self._data = collections.defaultdict(list)
+
+            q = self.subq
+            assert q.session is None
+
+            q = q.with_session(self.session)
+
+            if self.load_options._populate_existing:
+                q = q.populate_existing()
+            # to work with baked query, the parameters may have been
+            # updated since this query was created, so take these into account
+
+            rows = list(q.params(self.params))
+            for k, v in itertools.groupby(rows, lambda x: x[1:]):
+                self._data[k].extend(vv[0] for vv in v)
+
+        def loader(self, state, dict_, row):
+            if self._data is None:
+                self._load()
+
+    def _setup_query_from_rowproc(
+        self,
+        context,
+        query_entity,
+        path,
+        entity,
+        loadopt,
+        adapter,
+    ):
+        compile_state = context.compile_state
+        if (
+            not compile_state.compile_options._enable_eagerloads
+            or compile_state.compile_options._for_refresh_state
+        ):
+            return
+
+        orig_query_entity_index = compile_state._entities.index(query_entity)
+        context.loaders_require_buffering = True
+
+        path = path[self.parent_property]
+
+        # build up a path indicating the path from the leftmost
+        # entity to the thing we're subquery loading.
+        with_poly_entity = path.get(
+            compile_state.attributes, "path_with_polymorphic", None
+        )
+        if with_poly_entity is not None:
+            effective_entity = with_poly_entity
+        else:
+            effective_entity = self.entity
+
+        subq_path, rewritten_path = context.query._execution_options.get(
+            ("subquery_paths", None),
+            (orm_util.PathRegistry.root, orm_util.PathRegistry.root),
+        )
+        is_root = subq_path is orm_util.PathRegistry.root
+        subq_path = subq_path + path
+        rewritten_path = rewritten_path + path
+
+        # use the current query being invoked, not the compile state
+        # one.  this is so that we get the current parameters.  however,
+        # it means we can't use the existing compile state, we have to make
+        # a new one.    other approaches include possibly using the
+        # compiled query but swapping the params, seems only marginally
+        # less time spent but more complicated
+        orig_query = context.query._execution_options.get(
+            ("orig_query", SubqueryLoader), context.query
+        )
+
+        # make a new compile_state for the query that's probably cached, but
+        # we're sort of undoing a bit of that caching :(
+        compile_state_cls = ORMCompileState._get_plugin_class_for_plugin(
+            orig_query, "orm"
+        )
+
+        if orig_query._is_lambda_element:
+            if context.load_options._lazy_loaded_from is None:
+                util.warn(
+                    'subqueryloader for "%s" must invoke lambda callable '
+                    "at %r in "
+                    "order to produce a new query, decreasing the efficiency "
+                    "of caching for this statement.  Consider using "
+                    "selectinload() for more effective full-lambda caching"
+                    % (self, orig_query)
+                )
+            orig_query = orig_query._resolved
+
+        # this is the more "quick" version, however it's not clear how
+        # much of this we need.    in particular I can't get a test to
+        # fail if the "set_base_alias" is missing and not sure why that is.
+        orig_compile_state = compile_state_cls._create_entities_collection(
+            orig_query, legacy=False
+        )
+
+        (
+            leftmost_mapper,
+            leftmost_attr,
+            leftmost_relationship,
+            rewritten_path,
+        ) = self._get_leftmost(
+            orig_query_entity_index,
+            rewritten_path,
+            orig_compile_state,
+            is_root,
+        )
+
+        # generate a new Query from the original, then
+        # produce a subquery from it.
+        left_alias = self._generate_from_original_query(
+            orig_compile_state,
+            orig_query,
+            leftmost_mapper,
+            leftmost_attr,
+            leftmost_relationship,
+            entity,
+        )
+
+        # generate another Query that will join the
+        # left alias to the target relationships.
+        # basically doing a longhand
+        # "from_self()".  (from_self() itself not quite industrial
+        # strength enough for all contingencies...but very close)
+
+        q = query.Query(effective_entity)
+
+        q._execution_options = context.query._execution_options.merge_with(
+            context.execution_options,
+            {
+                ("orig_query", SubqueryLoader): orig_query,
+                ("subquery_paths", None): (subq_path, rewritten_path),
+            },
+        )
+
+        q = q._set_enable_single_crit(False)
+        to_join, local_attr, parent_alias = self._prep_for_joins(
+            left_alias, subq_path
+        )
+
+        q = q.add_columns(*local_attr)
+        q = self._apply_joins(
+            q, to_join, left_alias, parent_alias, effective_entity
+        )
+
+        q = self._setup_options(
+            context,
+            q,
+            subq_path,
+            rewritten_path,
+            orig_query,
+            effective_entity,
+            loadopt,
+        )
+        q = self._setup_outermost_orderby(q)
+
+        return q
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        if (
+            loadopt
+            and context.compile_state.statement is not None
+            and context.compile_state.statement.is_dml
+        ):
+            util.warn_deprecated(
+                "The subqueryload loader option is not compatible with DML "
+                "statements such as INSERT, UPDATE.  Only SELECT may be used."
+                "This warning will become an exception in a future release.",
+                "2.0",
+            )
+
+        if context.refresh_state:
+            return self._immediateload_create_row_processor(
+                context,
+                query_entity,
+                path,
+                loadopt,
+                mapper,
+                result,
+                adapter,
+                populators,
+            )
+
+        _, run_loader, _, _ = self._setup_for_recursion(
+            context, path, loadopt, self.join_depth
+        )
+        if not run_loader:
+            return
+
+        if not isinstance(context.compile_state, ORMSelectCompileState):
+            # issue 7505 - subqueryload() in 1.3 and previous would silently
+            # degrade for from_statement() without warning. this behavior
+            # is restored here
+            return
+
+        if not self.parent.class_manager[self.key].impl.supports_population:
+            raise sa_exc.InvalidRequestError(
+                "'%s' does not support object "
+                "population - eager loading cannot be applied." % self
+            )
+
+        # a little dance here as the "path" is still something that only
+        # semi-tracks the exact series of things we are loading, still not
+        # telling us about with_polymorphic() and stuff like that when it's at
+        # the root..  the initial MapperEntity is more accurate for this case.
+        if len(path) == 1:
+            if not orm_util._entity_isa(query_entity.entity_zero, self.parent):
+                return
+        elif not orm_util._entity_isa(path[-1], self.parent):
+            return
+
+        subq = self._setup_query_from_rowproc(
+            context,
+            query_entity,
+            path,
+            path[-1],
+            loadopt,
+            adapter,
+        )
+
+        if subq is None:
+            return
+
+        assert subq.session is None
+
+        path = path[self.parent_property]
+
+        local_cols = self.parent_property.local_columns
+
+        # cache the loaded collections in the context
+        # so that inheriting mappers don't re-load when they
+        # call upon create_row_processor again
+        collections = path.get(context.attributes, "collections")
+        if collections is None:
+            collections = self._SubqCollections(context, subq)
+            path.set(context.attributes, "collections", collections)
+
+        if adapter:
+            local_cols = [adapter.columns[c] for c in local_cols]
+
+        if self.uselist:
+            self._create_collection_loader(
+                context, result, collections, local_cols, populators
+            )
+        else:
+            self._create_scalar_loader(
+                context, result, collections, local_cols, populators
+            )
+
+    def _create_collection_loader(
+        self, context, result, collections, local_cols, populators
+    ):
+        tuple_getter = result._tuple_getter(local_cols)
+
+        def load_collection_from_subq(state, dict_, row):
+            collection = collections.get(tuple_getter(row), ())
+            state.get_impl(self.key).set_committed_value(
+                state, dict_, collection
+            )
+
+        def load_collection_from_subq_existing_row(state, dict_, row):
+            if self.key not in dict_:
+                load_collection_from_subq(state, dict_, row)
+
+        populators["new"].append((self.key, load_collection_from_subq))
+        populators["existing"].append(
+            (self.key, load_collection_from_subq_existing_row)
+        )
+
+        if context.invoke_all_eagers:
+            populators["eager"].append((self.key, collections.loader))
+
+    def _create_scalar_loader(
+        self, context, result, collections, local_cols, populators
+    ):
+        tuple_getter = result._tuple_getter(local_cols)
+
+        def load_scalar_from_subq(state, dict_, row):
+            collection = collections.get(tuple_getter(row), (None,))
+            if len(collection) > 1:
+                util.warn(
+                    "Multiple rows returned with "
+                    "uselist=False for eagerly-loaded attribute '%s' " % self
+                )
+
+            scalar = collection[0]
+            state.get_impl(self.key).set_committed_value(state, dict_, scalar)
+
+        def load_scalar_from_subq_existing_row(state, dict_, row):
+            if self.key not in dict_:
+                load_scalar_from_subq(state, dict_, row)
+
+        populators["new"].append((self.key, load_scalar_from_subq))
+        populators["existing"].append(
+            (self.key, load_scalar_from_subq_existing_row)
+        )
+        if context.invoke_all_eagers:
+            populators["eager"].append((self.key, collections.loader))
+
+
+@log.class_logger
+@relationships.RelationshipProperty.strategy_for(lazy="joined")
+@relationships.RelationshipProperty.strategy_for(lazy=False)
+class JoinedLoader(AbstractRelationshipLoader):
+    """Provide loading behavior for a :class:`.Relationship`
+    using joined eager loading.
+
+    """
+
+    __slots__ = "join_depth"
+
+    def __init__(self, parent, strategy_key):
+        super().__init__(parent, strategy_key)
+        self.join_depth = self.parent_property.join_depth
+
+    def init_class_attribute(self, mapper):
+        self.parent_property._get_strategy(
+            (("lazy", "select"),)
+        ).init_class_attribute(mapper)
+
+    def setup_query(
+        self,
+        compile_state,
+        query_entity,
+        path,
+        loadopt,
+        adapter,
+        column_collection=None,
+        parentmapper=None,
+        chained_from_outerjoin=False,
+        **kwargs,
+    ):
+        """Add a left outer join to the statement that's being constructed."""
+
+        if not compile_state.compile_options._enable_eagerloads:
+            return
+        elif (
+            loadopt
+            and compile_state.statement is not None
+            and compile_state.statement.is_dml
+        ):
+            util.warn_deprecated(
+                "The joinedload loader option is not compatible with DML "
+                "statements such as INSERT, UPDATE.  Only SELECT may be used."
+                "This warning will become an exception in a future release.",
+                "2.0",
+            )
+        elif self.uselist:
+            compile_state.multi_row_eager_loaders = True
+
+        path = path[self.parent_property]
+
+        with_polymorphic = None
+
+        user_defined_adapter = (
+            self._init_user_defined_eager_proc(
+                loadopt, compile_state, compile_state.attributes
+            )
+            if loadopt
+            else False
+        )
+
+        if user_defined_adapter is not False:
+            # setup an adapter but dont create any JOIN, assume it's already
+            # in the query
+            (
+                clauses,
+                adapter,
+                add_to_collection,
+            ) = self._setup_query_on_user_defined_adapter(
+                compile_state,
+                query_entity,
+                path,
+                adapter,
+                user_defined_adapter,
+            )
+
+            # don't do "wrap" for multi-row, we want to wrap
+            # limited/distinct SELECT,
+            # because we want to put the JOIN on the outside.
+
+        else:
+            # if not via query option, check for
+            # a cycle
+            if not path.contains(compile_state.attributes, "loader"):
+                if self.join_depth:
+                    if path.length / 2 > self.join_depth:
+                        return
+                elif path.contains_mapper(self.mapper):
+                    return
+
+            # add the JOIN and create an adapter
+            (
+                clauses,
+                adapter,
+                add_to_collection,
+                chained_from_outerjoin,
+            ) = self._generate_row_adapter(
+                compile_state,
+                query_entity,
+                path,
+                loadopt,
+                adapter,
+                column_collection,
+                parentmapper,
+                chained_from_outerjoin,
+            )
+
+            # for multi-row, we want to wrap limited/distinct SELECT,
+            # because we want to put the JOIN on the outside.
+            compile_state.eager_adding_joins = True
+
+        with_poly_entity = path.get(
+            compile_state.attributes, "path_with_polymorphic", None
+        )
+        if with_poly_entity is not None:
+            with_polymorphic = inspect(
+                with_poly_entity
+            ).with_polymorphic_mappers
+        else:
+            with_polymorphic = None
+
+        path = path[self.entity]
+
+        loading._setup_entity_query(
+            compile_state,
+            self.mapper,
+            query_entity,
+            path,
+            clauses,
+            add_to_collection,
+            with_polymorphic=with_polymorphic,
+            parentmapper=self.mapper,
+            chained_from_outerjoin=chained_from_outerjoin,
+        )
+
+        has_nones = util.NONE_SET.intersection(compile_state.secondary_columns)
+
+        if has_nones:
+            if with_poly_entity is not None:
+                raise sa_exc.InvalidRequestError(
+                    "Detected unaliased columns when generating joined "
+                    "load.  Make sure to use aliased=True or flat=True "
+                    "when using joined loading with with_polymorphic()."
+                )
+            else:
+                compile_state.secondary_columns = [
+                    c for c in compile_state.secondary_columns if c is not None
+                ]
+
+    def _init_user_defined_eager_proc(
+        self, loadopt, compile_state, target_attributes
+    ):
+        # check if the opt applies at all
+        if "eager_from_alias" not in loadopt.local_opts:
+            # nope
+            return False
+
+        path = loadopt.path.parent
+
+        # the option applies.  check if the "user_defined_eager_row_processor"
+        # has been built up.
+        adapter = path.get(
+            compile_state.attributes, "user_defined_eager_row_processor", False
+        )
+        if adapter is not False:
+            # just return it
+            return adapter
+
+        # otherwise figure it out.
+        alias = loadopt.local_opts["eager_from_alias"]
+        root_mapper, prop = path[-2:]
+
+        if alias is not None:
+            if isinstance(alias, str):
+                alias = prop.target.alias(alias)
+            adapter = orm_util.ORMAdapter(
+                orm_util._TraceAdaptRole.JOINEDLOAD_USER_DEFINED_ALIAS,
+                prop.mapper,
+                selectable=alias,
+                equivalents=prop.mapper._equivalent_columns,
+                limit_on_entity=False,
+            )
+        else:
+            if path.contains(
+                compile_state.attributes, "path_with_polymorphic"
+            ):
+                with_poly_entity = path.get(
+                    compile_state.attributes, "path_with_polymorphic"
+                )
+                adapter = orm_util.ORMAdapter(
+                    orm_util._TraceAdaptRole.JOINEDLOAD_PATH_WITH_POLYMORPHIC,
+                    with_poly_entity,
+                    equivalents=prop.mapper._equivalent_columns,
+                )
+            else:
+                adapter = compile_state._polymorphic_adapters.get(
+                    prop.mapper, None
+                )
+        path.set(
+            target_attributes,
+            "user_defined_eager_row_processor",
+            adapter,
+        )
+
+        return adapter
+
+    def _setup_query_on_user_defined_adapter(
+        self, context, entity, path, adapter, user_defined_adapter
+    ):
+        # apply some more wrapping to the "user defined adapter"
+        # if we are setting up the query for SQL render.
+        adapter = entity._get_entity_clauses(context)
+
+        if adapter and user_defined_adapter:
+            user_defined_adapter = user_defined_adapter.wrap(adapter)
+            path.set(
+                context.attributes,
+                "user_defined_eager_row_processor",
+                user_defined_adapter,
+            )
+        elif adapter:
+            user_defined_adapter = adapter
+            path.set(
+                context.attributes,
+                "user_defined_eager_row_processor",
+                user_defined_adapter,
+            )
+
+        add_to_collection = context.primary_columns
+        return user_defined_adapter, adapter, add_to_collection
+
+    def _generate_row_adapter(
+        self,
+        compile_state,
+        entity,
+        path,
+        loadopt,
+        adapter,
+        column_collection,
+        parentmapper,
+        chained_from_outerjoin,
+    ):
+        with_poly_entity = path.get(
+            compile_state.attributes, "path_with_polymorphic", None
+        )
+        if with_poly_entity:
+            to_adapt = with_poly_entity
+        else:
+            insp = inspect(self.entity)
+            if insp.is_aliased_class:
+                alt_selectable = insp.selectable
+            else:
+                alt_selectable = None
+
+            to_adapt = orm_util.AliasedClass(
+                self.mapper,
+                alias=(
+                    alt_selectable._anonymous_fromclause(flat=True)
+                    if alt_selectable is not None
+                    else None
+                ),
+                flat=True,
+                use_mapper_path=True,
+            )
+
+        to_adapt_insp = inspect(to_adapt)
+
+        clauses = to_adapt_insp._memo(
+            ("joinedloader_ormadapter", self),
+            orm_util.ORMAdapter,
+            orm_util._TraceAdaptRole.JOINEDLOAD_MEMOIZED_ADAPTER,
+            to_adapt_insp,
+            equivalents=self.mapper._equivalent_columns,
+            adapt_required=True,
+            allow_label_resolve=False,
+            anonymize_labels=True,
+        )
+
+        assert clauses.is_aliased_class
+
+        innerjoin = (
+            loadopt.local_opts.get("innerjoin", self.parent_property.innerjoin)
+            if loadopt is not None
+            else self.parent_property.innerjoin
+        )
+
+        if not innerjoin:
+            # if this is an outer join, all non-nested eager joins from
+            # this path must also be outer joins
+            chained_from_outerjoin = True
+
+        compile_state.create_eager_joins.append(
+            (
+                self._create_eager_join,
+                entity,
+                path,
+                adapter,
+                parentmapper,
+                clauses,
+                innerjoin,
+                chained_from_outerjoin,
+                loadopt._extra_criteria if loadopt else (),
+            )
+        )
+
+        add_to_collection = compile_state.secondary_columns
+        path.set(compile_state.attributes, "eager_row_processor", clauses)
+
+        return clauses, adapter, add_to_collection, chained_from_outerjoin
+
+    def _create_eager_join(
+        self,
+        compile_state,
+        query_entity,
+        path,
+        adapter,
+        parentmapper,
+        clauses,
+        innerjoin,
+        chained_from_outerjoin,
+        extra_criteria,
+    ):
+        if parentmapper is None:
+            localparent = query_entity.mapper
+        else:
+            localparent = parentmapper
+
+        # whether or not the Query will wrap the selectable in a subquery,
+        # and then attach eager load joins to that (i.e., in the case of
+        # LIMIT/OFFSET etc.)
+        should_nest_selectable = (
+            compile_state.multi_row_eager_loaders
+            and compile_state._should_nest_selectable
+        )
+
+        query_entity_key = None
+
+        if (
+            query_entity not in compile_state.eager_joins
+            and not should_nest_selectable
+            and compile_state.from_clauses
+        ):
+            indexes = sql_util.find_left_clause_that_matches_given(
+                compile_state.from_clauses, query_entity.selectable
+            )
+
+            if len(indexes) > 1:
+                # for the eager load case, I can't reproduce this right
+                # now.   For query.join() I can.
+                raise sa_exc.InvalidRequestError(
+                    "Can't identify which query entity in which to joined "
+                    "eager load from.   Please use an exact match when "
+                    "specifying the join path."
+                )
+
+            if indexes:
+                clause = compile_state.from_clauses[indexes[0]]
+                # join to an existing FROM clause on the query.
+                # key it to its list index in the eager_joins dict.
+                # Query._compile_context will adapt as needed and
+                # append to the FROM clause of the select().
+                query_entity_key, default_towrap = indexes[0], clause
+
+        if query_entity_key is None:
+            query_entity_key, default_towrap = (
+                query_entity,
+                query_entity.selectable,
+            )
+
+        towrap = compile_state.eager_joins.setdefault(
+            query_entity_key, default_towrap
+        )
+
+        if adapter:
+            if getattr(adapter, "is_aliased_class", False):
+                # joining from an adapted entity.  The adapted entity
+                # might be a "with_polymorphic", so resolve that to our
+                # specific mapper's entity before looking for our attribute
+                # name on it.
+                efm = adapter.aliased_insp._entity_for_mapper(
+                    localparent
+                    if localparent.isa(self.parent)
+                    else self.parent
+                )
+
+                # look for our attribute on the adapted entity, else fall back
+                # to our straight property
+                onclause = getattr(efm.entity, self.key, self.parent_property)
+            else:
+                onclause = getattr(
+                    orm_util.AliasedClass(
+                        self.parent, adapter.selectable, use_mapper_path=True
+                    ),
+                    self.key,
+                    self.parent_property,
+                )
+
+        else:
+            onclause = self.parent_property
+
+        assert clauses.is_aliased_class
+
+        attach_on_outside = (
+            not chained_from_outerjoin
+            or not innerjoin
+            or innerjoin == "unnested"
+            or query_entity.entity_zero.represents_outer_join
+        )
+
+        extra_join_criteria = extra_criteria
+        additional_entity_criteria = compile_state.global_attributes.get(
+            ("additional_entity_criteria", self.mapper), ()
+        )
+        if additional_entity_criteria:
+            extra_join_criteria += tuple(
+                ae._resolve_where_criteria(self.mapper)
+                for ae in additional_entity_criteria
+                if ae.propagate_to_loaders
+            )
+
+        if attach_on_outside:
+            # this is the "classic" eager join case.
+            eagerjoin = orm_util._ORMJoin(
+                towrap,
+                clauses.aliased_insp,
+                onclause,
+                isouter=not innerjoin
+                or query_entity.entity_zero.represents_outer_join
+                or (chained_from_outerjoin and isinstance(towrap, sql.Join)),
+                _left_memo=self.parent,
+                _right_memo=path[self.mapper],
+                _extra_criteria=extra_join_criteria,
+            )
+        else:
+            # all other cases are innerjoin=='nested' approach
+            eagerjoin = self._splice_nested_inner_join(
+                path, path[-2], towrap, clauses, onclause, extra_join_criteria
+            )
+
+        compile_state.eager_joins[query_entity_key] = eagerjoin
+
+        # send a hint to the Query as to where it may "splice" this join
+        eagerjoin.stop_on = query_entity.selectable
+
+        if not parentmapper:
+            # for parentclause that is the non-eager end of the join,
+            # ensure all the parent cols in the primaryjoin are actually
+            # in the
+            # columns clause (i.e. are not deferred), so that aliasing applied
+            # by the Query propagates those columns outward.
+            # This has the effect
+            # of "undefering" those columns.
+            for col in sql_util._find_columns(
+                self.parent_property.primaryjoin
+            ):
+                if localparent.persist_selectable.c.contains_column(col):
+                    if adapter:
+                        col = adapter.columns[col]
+                    compile_state._append_dedupe_col_collection(
+                        col, compile_state.primary_columns
+                    )
+
+        if self.parent_property.order_by:
+            compile_state.eager_order_by += tuple(
+                (eagerjoin._target_adapter.copy_and_process)(
+                    util.to_list(self.parent_property.order_by)
+                )
+            )
+
+    def _splice_nested_inner_join(
+        self,
+        path,
+        entity_we_want_to_splice_onto,
+        join_obj,
+        clauses,
+        onclause,
+        extra_criteria,
+        entity_inside_join_structure: Union[
+            Mapper, None, Literal[False]
+        ] = False,
+        detected_existing_path: Optional[path_registry.PathRegistry] = None,
+    ):
+        # recursive fn to splice a nested join into an existing one.
+        # entity_inside_join_structure=False means this is the outermost call,
+        # and it should return a value.  entity_inside_join_structure=<mapper>
+        # indicates we've descended into a join and are looking at a FROM
+        # clause representing this mapper; if this is not
+        # entity_we_want_to_splice_onto then return None to end the recursive
+        # branch
+
+        assert entity_we_want_to_splice_onto is path[-2]
+
+        if entity_inside_join_structure is False:
+            assert isinstance(join_obj, orm_util._ORMJoin)
+
+        if isinstance(join_obj, sql.selectable.FromGrouping):
+            # FromGrouping - continue descending into the structure
+            return self._splice_nested_inner_join(
+                path,
+                entity_we_want_to_splice_onto,
+                join_obj.element,
+                clauses,
+                onclause,
+                extra_criteria,
+                entity_inside_join_structure,
+            )
+        elif isinstance(join_obj, orm_util._ORMJoin):
+            # _ORMJoin - continue descending into the structure
+
+            join_right_path = join_obj._right_memo
+
+            # see if right side of join is viable
+            target_join = self._splice_nested_inner_join(
+                path,
+                entity_we_want_to_splice_onto,
+                join_obj.right,
+                clauses,
+                onclause,
+                extra_criteria,
+                entity_inside_join_structure=(
+                    join_right_path[-1].mapper
+                    if join_right_path is not None
+                    else None
+                ),
+            )
+
+            if target_join is not None:
+                # for a right splice, attempt to flatten out
+                # a JOIN b JOIN c JOIN .. to avoid needless
+                # parenthesis nesting
+                if not join_obj.isouter and not target_join.isouter:
+                    eagerjoin = join_obj._splice_into_center(target_join)
+                else:
+                    eagerjoin = orm_util._ORMJoin(
+                        join_obj.left,
+                        target_join,
+                        join_obj.onclause,
+                        isouter=join_obj.isouter,
+                        _left_memo=join_obj._left_memo,
+                    )
+
+                eagerjoin._target_adapter = target_join._target_adapter
+                return eagerjoin
+
+            else:
+                # see if left side of join is viable
+                target_join = self._splice_nested_inner_join(
+                    path,
+                    entity_we_want_to_splice_onto,
+                    join_obj.left,
+                    clauses,
+                    onclause,
+                    extra_criteria,
+                    entity_inside_join_structure=join_obj._left_memo,
+                    detected_existing_path=join_right_path,
+                )
+
+                if target_join is not None:
+                    eagerjoin = orm_util._ORMJoin(
+                        target_join,
+                        join_obj.right,
+                        join_obj.onclause,
+                        isouter=join_obj.isouter,
+                        _right_memo=join_obj._right_memo,
+                    )
+                    eagerjoin._target_adapter = target_join._target_adapter
+                    return eagerjoin
+
+            # neither side viable, return None, or fail if this was the top
+            # most call
+            if entity_inside_join_structure is False:
+                assert (
+                    False
+                ), "assertion failed attempting to produce joined eager loads"
+            return None
+
+        # reached an endpoint (e.g. a table that's mapped, or an alias of that
+        # table).  determine if we can use this endpoint to splice onto
+
+        # is this the entity we want to splice onto in the first place?
+        if not entity_we_want_to_splice_onto.isa(entity_inside_join_structure):
+            return None
+
+        # path check.  if we know the path how this join endpoint got here,
+        # lets look at our path we are satisfying and see if we're in the
+        # wrong place.  This is specifically for when our entity may
+        # appear more than once in the path, issue #11449
+        # updated in issue #11965.
+        if detected_existing_path and len(detected_existing_path) > 2:
+            # this assertion is currently based on how this call is made,
+            # where given a join_obj, the call will have these parameters as
+            # entity_inside_join_structure=join_obj._left_memo
+            # and entity_inside_join_structure=join_obj._right_memo.mapper
+            assert detected_existing_path[-3] is entity_inside_join_structure
+
+            # from that, see if the path we are targeting matches the
+            # "existing" path of this join all the way up to the midpoint
+            # of this join object (e.g. the relationship).
+            # if not, then this is not our target
+            #
+            # a test condition where this test is false looks like:
+            #
+            # desired splice:         Node->kind->Kind
+            # path of desired splice: NodeGroup->nodes->Node->kind
+            # path we've located:     NodeGroup->nodes->Node->common_node->Node
+            #
+            # above, because we want to splice kind->Kind onto
+            # NodeGroup->nodes->Node, this is not our path because it actually
+            # goes more steps than we want into self-referential
+            # ->common_node->Node
+            #
+            # a test condition where this test is true looks like:
+            #
+            # desired splice:         B->c2s->C2
+            # path of desired splice: A->bs->B->c2s
+            # path we've located:     A->bs->B->c1s->C1
+            #
+            # above, we want to splice c2s->C2 onto B, and the located path
+            # shows that the join ends with B->c1s->C1.  so we will
+            # add another join onto that, which would create a "branch" that
+            # we might represent in a pseudopath as:
+            #
+            # B->c1s->C1
+            #  ->c2s->C2
+            #
+            # i.e. A JOIN B ON <bs> JOIN C1 ON <c1s>
+            #                       JOIN C2 ON <c2s>
+            #
+
+            if detected_existing_path[0:-2] != path.path[0:-1]:
+                return None
+
+        return orm_util._ORMJoin(
+            join_obj,
+            clauses.aliased_insp,
+            onclause,
+            isouter=False,
+            _left_memo=entity_inside_join_structure,
+            _right_memo=path[path[-1].mapper],
+            _extra_criteria=extra_criteria,
+        )
+
+    def _create_eager_adapter(self, context, result, adapter, path, loadopt):
+        compile_state = context.compile_state
+
+        user_defined_adapter = (
+            self._init_user_defined_eager_proc(
+                loadopt, compile_state, context.attributes
+            )
+            if loadopt
+            else False
+        )
+
+        if user_defined_adapter is not False:
+            decorator = user_defined_adapter
+            # user defined eagerloads are part of the "primary"
+            # portion of the load.
+            # the adapters applied to the Query should be honored.
+            if compile_state.compound_eager_adapter and decorator:
+                decorator = decorator.wrap(
+                    compile_state.compound_eager_adapter
+                )
+            elif compile_state.compound_eager_adapter:
+                decorator = compile_state.compound_eager_adapter
+        else:
+            decorator = path.get(
+                compile_state.attributes, "eager_row_processor"
+            )
+            if decorator is None:
+                return False
+
+        if self.mapper._result_has_identity_key(result, decorator):
+            return decorator
+        else:
+            # no identity key - don't return a row
+            # processor, will cause a degrade to lazy
+            return False
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+
+        if not context.compile_state.compile_options._enable_eagerloads:
+            return
+
+        if not self.parent.class_manager[self.key].impl.supports_population:
+            raise sa_exc.InvalidRequestError(
+                "'%s' does not support object "
+                "population - eager loading cannot be applied." % self
+            )
+
+        if self.uselist:
+            context.loaders_require_uniquing = True
+
+        our_path = path[self.parent_property]
+
+        eager_adapter = self._create_eager_adapter(
+            context, result, adapter, our_path, loadopt
+        )
+
+        if eager_adapter is not False:
+            key = self.key
+
+            _instance = loading._instance_processor(
+                query_entity,
+                self.mapper,
+                context,
+                result,
+                our_path[self.entity],
+                eager_adapter,
+            )
+
+            if not self.uselist:
+                self._create_scalar_loader(context, key, _instance, populators)
+            else:
+                self._create_collection_loader(
+                    context, key, _instance, populators
+                )
+        else:
+            self.parent_property._get_strategy(
+                (("lazy", "select"),)
+            ).create_row_processor(
+                context,
+                query_entity,
+                path,
+                loadopt,
+                mapper,
+                result,
+                adapter,
+                populators,
+            )
+
+    def _create_collection_loader(self, context, key, _instance, populators):
+        def load_collection_from_joined_new_row(state, dict_, row):
+            # note this must unconditionally clear out any existing collection.
+            # an existing collection would be present only in the case of
+            # populate_existing().
+            collection = attributes.init_state_collection(state, dict_, key)
+            result_list = util.UniqueAppender(
+                collection, "append_without_event"
+            )
+            context.attributes[(state, key)] = result_list
+            inst = _instance(row)
+            if inst is not None:
+                result_list.append(inst)
+
+        def load_collection_from_joined_existing_row(state, dict_, row):
+            if (state, key) in context.attributes:
+                result_list = context.attributes[(state, key)]
+            else:
+                # appender_key can be absent from context.attributes
+                # with isnew=False when self-referential eager loading
+                # is used; the same instance may be present in two
+                # distinct sets of result columns
+                collection = attributes.init_state_collection(
+                    state, dict_, key
+                )
+                result_list = util.UniqueAppender(
+                    collection, "append_without_event"
+                )
+                context.attributes[(state, key)] = result_list
+            inst = _instance(row)
+            if inst is not None:
+                result_list.append(inst)
+
+        def load_collection_from_joined_exec(state, dict_, row):
+            _instance(row)
+
+        populators["new"].append(
+            (self.key, load_collection_from_joined_new_row)
+        )
+        populators["existing"].append(
+            (self.key, load_collection_from_joined_existing_row)
+        )
+        if context.invoke_all_eagers:
+            populators["eager"].append(
+                (self.key, load_collection_from_joined_exec)
+            )
+
+    def _create_scalar_loader(self, context, key, _instance, populators):
+        def load_scalar_from_joined_new_row(state, dict_, row):
+            # set a scalar object instance directly on the parent
+            # object, bypassing InstrumentedAttribute event handlers.
+            dict_[key] = _instance(row)
+
+        def load_scalar_from_joined_existing_row(state, dict_, row):
+            # call _instance on the row, even though the object has
+            # been created, so that we further descend into properties
+            existing = _instance(row)
+
+            # conflicting value already loaded, this shouldn't happen
+            if key in dict_:
+                if existing is not dict_[key]:
+                    util.warn(
+                        "Multiple rows returned with "
+                        "uselist=False for eagerly-loaded attribute '%s' "
+                        % self
+                    )
+            else:
+                # this case is when one row has multiple loads of the
+                # same entity (e.g. via aliasing), one has an attribute
+                # that the other doesn't.
+                dict_[key] = existing
+
+        def load_scalar_from_joined_exec(state, dict_, row):
+            _instance(row)
+
+        populators["new"].append((self.key, load_scalar_from_joined_new_row))
+        populators["existing"].append(
+            (self.key, load_scalar_from_joined_existing_row)
+        )
+        if context.invoke_all_eagers:
+            populators["eager"].append(
+                (self.key, load_scalar_from_joined_exec)
+            )
+
+
+@log.class_logger
+@relationships.RelationshipProperty.strategy_for(lazy="selectin")
+class SelectInLoader(PostLoader, util.MemoizedSlots):
+    __slots__ = (
+        "join_depth",
+        "omit_join",
+        "_parent_alias",
+        "_query_info",
+        "_fallback_query_info",
+    )
+
+    query_info = collections.namedtuple(
+        "queryinfo",
+        [
+            "load_only_child",
+            "load_with_join",
+            "in_expr",
+            "pk_cols",
+            "zero_idx",
+            "child_lookup_cols",
+        ],
+    )
+
+    _chunksize = 500
+
+    def __init__(self, parent, strategy_key):
+        super().__init__(parent, strategy_key)
+        self.join_depth = self.parent_property.join_depth
+        is_m2o = self.parent_property.direction is interfaces.MANYTOONE
+
+        if self.parent_property.omit_join is not None:
+            self.omit_join = self.parent_property.omit_join
+        else:
+            lazyloader = self.parent_property._get_strategy(
+                (("lazy", "select"),)
+            )
+            if is_m2o:
+                self.omit_join = lazyloader.use_get
+            else:
+                self.omit_join = self.parent._get_clause[0].compare(
+                    lazyloader._rev_lazywhere,
+                    use_proxies=True,
+                    compare_keys=False,
+                    equivalents=self.parent._equivalent_columns,
+                )
+
+        if self.omit_join:
+            if is_m2o:
+                self._query_info = self._init_for_omit_join_m2o()
+                self._fallback_query_info = self._init_for_join()
+            else:
+                self._query_info = self._init_for_omit_join()
+        else:
+            self._query_info = self._init_for_join()
+
+    def _init_for_omit_join(self):
+        pk_to_fk = dict(
+            self.parent_property._join_condition.local_remote_pairs
+        )
+        pk_to_fk.update(
+            (equiv, pk_to_fk[k])
+            for k in list(pk_to_fk)
+            for equiv in self.parent._equivalent_columns.get(k, ())
+        )
+
+        pk_cols = fk_cols = [
+            pk_to_fk[col] for col in self.parent.primary_key if col in pk_to_fk
+        ]
+        if len(fk_cols) > 1:
+            in_expr = sql.tuple_(*fk_cols)
+            zero_idx = False
+        else:
+            in_expr = fk_cols[0]
+            zero_idx = True
+
+        return self.query_info(False, False, in_expr, pk_cols, zero_idx, None)
+
+    def _init_for_omit_join_m2o(self):
+        pk_cols = self.mapper.primary_key
+        if len(pk_cols) > 1:
+            in_expr = sql.tuple_(*pk_cols)
+            zero_idx = False
+        else:
+            in_expr = pk_cols[0]
+            zero_idx = True
+
+        lazyloader = self.parent_property._get_strategy((("lazy", "select"),))
+        lookup_cols = [lazyloader._equated_columns[pk] for pk in pk_cols]
+
+        return self.query_info(
+            True, False, in_expr, pk_cols, zero_idx, lookup_cols
+        )
+
+    def _init_for_join(self):
+        self._parent_alias = AliasedClass(self.parent.class_)
+        pa_insp = inspect(self._parent_alias)
+        pk_cols = [
+            pa_insp._adapt_element(col) for col in self.parent.primary_key
+        ]
+        if len(pk_cols) > 1:
+            in_expr = sql.tuple_(*pk_cols)
+            zero_idx = False
+        else:
+            in_expr = pk_cols[0]
+            zero_idx = True
+        return self.query_info(False, True, in_expr, pk_cols, zero_idx, None)
+
+    def init_class_attribute(self, mapper):
+        self.parent_property._get_strategy(
+            (("lazy", "select"),)
+        ).init_class_attribute(mapper)
+
+    def create_row_processor(
+        self,
+        context,
+        query_entity,
+        path,
+        loadopt,
+        mapper,
+        result,
+        adapter,
+        populators,
+    ):
+        if context.refresh_state:
+            return self._immediateload_create_row_processor(
+                context,
+                query_entity,
+                path,
+                loadopt,
+                mapper,
+                result,
+                adapter,
+                populators,
+            )
+
+        (
+            effective_path,
+            run_loader,
+            execution_options,
+            recursion_depth,
+        ) = self._setup_for_recursion(
+            context, path, loadopt, join_depth=self.join_depth
+        )
+
+        if not run_loader:
+            return
+
+        if not context.compile_state.compile_options._enable_eagerloads:
+            return
+
+        if not self.parent.class_manager[self.key].impl.supports_population:
+            raise sa_exc.InvalidRequestError(
+                "'%s' does not support object "
+                "population - eager loading cannot be applied." % self
+            )
+
+        # a little dance here as the "path" is still something that only
+        # semi-tracks the exact series of things we are loading, still not
+        # telling us about with_polymorphic() and stuff like that when it's at
+        # the root..  the initial MapperEntity is more accurate for this case.
+        if len(path) == 1:
+            if not orm_util._entity_isa(query_entity.entity_zero, self.parent):
+                return
+        elif not orm_util._entity_isa(path[-1], self.parent):
+            return
+
+        selectin_path = effective_path
+
+        path_w_prop = path[self.parent_property]
+
+        # build up a path indicating the path from the leftmost
+        # entity to the thing we're subquery loading.
+        with_poly_entity = path_w_prop.get(
+            context.attributes, "path_with_polymorphic", None
+        )
+        if with_poly_entity is not None:
+            effective_entity = inspect(with_poly_entity)
+        else:
+            effective_entity = self.entity
+
+        loading.PostLoad.callable_for_path(
+            context,
+            selectin_path,
+            self.parent,
+            self.parent_property,
+            self._load_for_path,
+            effective_entity,
+            loadopt,
+            recursion_depth,
+            execution_options,
+        )
+
+    def _load_for_path(
+        self,
+        context,
+        path,
+        states,
+        load_only,
+        effective_entity,
+        loadopt,
+        recursion_depth,
+        execution_options,
+    ):
+        if load_only and self.key not in load_only:
+            return
+
+        query_info = self._query_info
+
+        if query_info.load_only_child:
+            our_states = collections.defaultdict(list)
+            none_states = []
+
+            mapper = self.parent
+
+            for state, overwrite in states:
+                state_dict = state.dict
+                related_ident = tuple(
+                    mapper._get_state_attr_by_column(
+                        state,
+                        state_dict,
+                        lk,
+                        passive=attributes.PASSIVE_NO_FETCH,
+                    )
+                    for lk in query_info.child_lookup_cols
+                )
+                # if the loaded parent objects do not have the foreign key
+                # to the related item loaded, then degrade into the joined
+                # version of selectinload
+                if LoaderCallableStatus.PASSIVE_NO_RESULT in related_ident:
+                    query_info = self._fallback_query_info
+                    break
+
+                # organize states into lists keyed to particular foreign
+                # key values.
+                if None not in related_ident:
+                    our_states[related_ident].append(
+                        (state, state_dict, overwrite)
+                    )
+                else:
+                    # For FK values that have None, add them to a
+                    # separate collection that will be populated separately
+                    none_states.append((state, state_dict, overwrite))
+
+        # note the above conditional may have changed query_info
+        if not query_info.load_only_child:
+            our_states = [
+                (state.key[1], state, state.dict, overwrite)
+                for state, overwrite in states
+            ]
+
+        pk_cols = query_info.pk_cols
+        in_expr = query_info.in_expr
+
+        if not query_info.load_with_join:
+            # in "omit join" mode, the primary key column and the
+            # "in" expression are in terms of the related entity.  So
+            # if the related entity is polymorphic or otherwise aliased,
+            # we need to adapt our "pk_cols" and "in_expr" to that
+            # entity.   in non-"omit join" mode, these are against the
+            # parent entity and do not need adaption.
+            if effective_entity.is_aliased_class:
+                pk_cols = [
+                    effective_entity._adapt_element(col) for col in pk_cols
+                ]
+                in_expr = effective_entity._adapt_element(in_expr)
+
+        bundle_ent = orm_util.Bundle("pk", *pk_cols)
+        bundle_sql = bundle_ent.__clause_element__()
+
+        entity_sql = effective_entity.__clause_element__()
+        q = Select._create_raw_select(
+            _raw_columns=[bundle_sql, entity_sql],
+            _label_style=LABEL_STYLE_TABLENAME_PLUS_COL,
+            _compile_options=ORMCompileState.default_compile_options,
+            _propagate_attrs={
+                "compile_state_plugin": "orm",
+                "plugin_subject": effective_entity,
+            },
+        )
+
+        if not query_info.load_with_join:
+            # the Bundle we have in the "omit_join" case is against raw, non
+            # annotated columns, so to ensure the Query knows its primary
+            # entity, we add it explicitly.  If we made the Bundle against
+            # annotated columns, we hit a performance issue in this specific
+            # case, which is detailed in issue #4347.
+            q = q.select_from(effective_entity)
+        else:
+            # in the non-omit_join case, the Bundle is against the annotated/
+            # mapped column of the parent entity, but the #4347 issue does not
+            # occur in this case.
+            q = q.select_from(self._parent_alias).join(
+                getattr(self._parent_alias, self.parent_property.key).of_type(
+                    effective_entity
+                )
+            )
+
+        q = q.filter(in_expr.in_(sql.bindparam("primary_keys")))
+
+        # a test which exercises what these comments talk about is
+        # test_selectin_relations.py -> test_twolevel_selectin_w_polymorphic
+        #
+        # effective_entity above is given to us in terms of the cached
+        # statement, namely this one:
+        orig_query = context.compile_state.select_statement
+
+        # the actual statement that was requested is this one:
+        #  context_query = context.user_passed_query
+        #
+        # that's not the cached one, however.  So while it is of the identical
+        # structure, if it has entities like AliasedInsp, which we get from
+        # aliased() or with_polymorphic(), the AliasedInsp will likely be a
+        # different object identity each time, and will not match up
+        # hashing-wise to the corresponding AliasedInsp that's in the
+        # cached query, meaning it won't match on paths and loader lookups
+        # and loaders like this one will be skipped if it is used in options.
+        #
+        # as it turns out, standard loader options like selectinload(),
+        # lazyload() that have a path need
+        # to come from the cached query so that the AliasedInsp etc. objects
+        # that are in the query line up with the object that's in the path
+        # of the strategy object. however other options like
+        # with_loader_criteria() that doesn't have a path (has a fixed entity)
+        # and needs to have access to the latest closure state in order to
+        # be correct, we need to use the uncached one.
+        #
+        # as of #8399 we let the loader option itself figure out what it
+        # wants to do given cached and uncached version of itself.
+
+        effective_path = path[self.parent_property]
+
+        if orig_query is context.user_passed_query:
+            new_options = orig_query._with_options
+        else:
+            cached_options = orig_query._with_options
+            uncached_options = context.user_passed_query._with_options
+
+            # propagate compile state options from the original query,
+            # updating their "extra_criteria" as necessary.
+            # note this will create a different cache key than
+            # "orig" options if extra_criteria is present, because the copy
+            # of extra_criteria will have different boundparam than that of
+            # the QueryableAttribute in the path
+            new_options = [
+                orig_opt._adapt_cached_option_to_uncached_option(
+                    context, uncached_opt
+                )
+                for orig_opt, uncached_opt in zip(
+                    cached_options, uncached_options
+                )
+            ]
+
+        if loadopt and loadopt._extra_criteria:
+            new_options += (
+                orm_util.LoaderCriteriaOption(
+                    effective_entity,
+                    loadopt._generate_extra_criteria(context),
+                ),
+            )
+
+        if recursion_depth is not None:
+            effective_path = effective_path._truncate_recursive()
+
+        q = q.options(*new_options)
+
+        q = q._update_compile_options({"_current_path": effective_path})
+        if context.populate_existing:
+            q = q.execution_options(populate_existing=True)
+
+        if self.parent_property.order_by:
+            if not query_info.load_with_join:
+                eager_order_by = self.parent_property.order_by
+                if effective_entity.is_aliased_class:
+                    eager_order_by = [
+                        effective_entity._adapt_element(elem)
+                        for elem in eager_order_by
+                    ]
+                q = q.order_by(*eager_order_by)
+            else:
+
+                def _setup_outermost_orderby(compile_context):
+                    compile_context.eager_order_by += tuple(
+                        util.to_list(self.parent_property.order_by)
+                    )
+
+                q = q._add_context_option(
+                    _setup_outermost_orderby, self.parent_property
+                )
+
+        if query_info.load_only_child:
+            self._load_via_child(
+                our_states,
+                none_states,
+                query_info,
+                q,
+                context,
+                execution_options,
+            )
+        else:
+            self._load_via_parent(
+                our_states, query_info, q, context, execution_options
+            )
+
+    def _load_via_child(
+        self,
+        our_states,
+        none_states,
+        query_info,
+        q,
+        context,
+        execution_options,
+    ):
+        uselist = self.uselist
+
+        # this sort is really for the benefit of the unit tests
+        our_keys = sorted(our_states)
+        while our_keys:
+            chunk = our_keys[0 : self._chunksize]
+            our_keys = our_keys[self._chunksize :]
+            data = {
+                k: v
+                for k, v in context.session.execute(
+                    q,
+                    params={
+                        "primary_keys": [
+                            key[0] if query_info.zero_idx else key
+                            for key in chunk
+                        ]
+                    },
+                    execution_options=execution_options,
+                ).unique()
+            }
+
+            for key in chunk:
+                # for a real foreign key and no concurrent changes to the
+                # DB while running this method, "key" is always present in
+                # data.  However, for primaryjoins without real foreign keys
+                # a non-None primaryjoin condition may still refer to no
+                # related object.
+                related_obj = data.get(key, None)
+                for state, dict_, overwrite in our_states[key]:
+                    if not overwrite and self.key in dict_:
+                        continue
+
+                    state.get_impl(self.key).set_committed_value(
+                        state,
+                        dict_,
+                        related_obj if not uselist else [related_obj],
+                    )
+        # populate none states with empty value / collection
+        for state, dict_, overwrite in none_states:
+            if not overwrite and self.key in dict_:
+                continue
+
+            # note it's OK if this is a uselist=True attribute, the empty
+            # collection will be populated
+            state.get_impl(self.key).set_committed_value(state, dict_, None)
+
+    def _load_via_parent(
+        self, our_states, query_info, q, context, execution_options
+    ):
+        uselist = self.uselist
+        _empty_result = () if uselist else None
+
+        while our_states:
+            chunk = our_states[0 : self._chunksize]
+            our_states = our_states[self._chunksize :]
+
+            primary_keys = [
+                key[0] if query_info.zero_idx else key
+                for key, state, state_dict, overwrite in chunk
+            ]
+
+            data = collections.defaultdict(list)
+            for k, v in itertools.groupby(
+                context.session.execute(
+                    q,
+                    params={"primary_keys": primary_keys},
+                    execution_options=execution_options,
+                ).unique(),
+                lambda x: x[0],
+            ):
+                data[k].extend(vv[1] for vv in v)
+
+            for key, state, state_dict, overwrite in chunk:
+                if not overwrite and self.key in state_dict:
+                    continue
+
+                collection = data.get(key, _empty_result)
+
+                if not uselist and collection:
+                    if len(collection) > 1:
+                        util.warn(
+                            "Multiple rows returned with "
+                            "uselist=False for eagerly-loaded "
+                            "attribute '%s' " % self
+                        )
+                    state.get_impl(self.key).set_committed_value(
+                        state, state_dict, collection[0]
+                    )
+                else:
+                    # note that empty tuple set on uselist=False sets the
+                    # value to None
+                    state.get_impl(self.key).set_committed_value(
+                        state, state_dict, collection
+                    )
+
+
+def single_parent_validator(desc, prop):
+    def _do_check(state, value, oldvalue, initiator):
+        if value is not None and initiator.key == prop.key:
+            hasparent = initiator.hasparent(attributes.instance_state(value))
+            if hasparent and oldvalue is not value:
+                raise sa_exc.InvalidRequestError(
+                    "Instance %s is already associated with an instance "
+                    "of %s via its %s attribute, and is only allowed a "
+                    "single parent."
+                    % (orm_util.instance_str(value), state.class_, prop),
+                    code="bbf1",
+                )
+        return value
+
+    def append(state, value, initiator):
+        return _do_check(state, value, None, initiator)
+
+    def set_(state, value, oldvalue, initiator):
+        return _do_check(state, value, oldvalue, initiator)
+
+    event.listen(
+        desc, "append", append, raw=True, retval=True, active_history=True
+    )
+    event.listen(desc, "set", set_, raw=True, retval=True, active_history=True)