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"""Methods for fetching data from the matrix stored in LMDB"""
from typing import Optional
from dataclasses import dataclass
import struct
import json
import lmdb
BLOB_HASH_DIGEST = 32
@dataclass
class Matrix:
"""Store sample data and any other relevant metadata"""
data: list
metadata: dict
def get_current_matrix(db_path: str) -> Optional[Matrix]:
"""Get the most recent matrix from DB_PATH. This is functionally
equivalent to get_nth_matrix(0, db_path)"""
env = lmdb.open(db_path)
with env.begin(write=False) as txn:
current_hash = txn.get(b"current") or b""
matrix_hash = txn.get(current_hash + b":matrix") or b""
row_pointers = txn.get(matrix_hash + b":row-pointers")
nrows = 0
if matrix_hash:
(nrows,) = struct.unpack("<Q", txn.get(matrix_hash + b":nrows"))
data, metadata = None, None
if row_pointers:
return Matrix(
data=[
json.loads(txn.get(row_pointers[i: i + 32]).decode())
for i in range(0, nrows * 32, 32)
],
metadata=json.loads(
txn.get(matrix_hash + b":metadata")
.rstrip(b"\x00")
.decode()
),
)
return None
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