Improve error reporting for no mapping results

* wqflask/wqflask/marker_regression/exceptions.py: new
  NoMappingResultsError exception
* wqflask/wqflask/templates/mapping_error.html: reword display of the
  errors
* wqflask/wqflask/views.py: Raise the NoMappingResultsError exception
  in the case where there are no results for the mapping.

3 files changed, 25 insertions, 5 deletions

diff --git a/wqflask/wqflask/marker_regression/exceptions.py b/wqflask/wqflask/marker_regression/exceptions.py
new file mode 100644
index 00000000..8c7e822b
--- /dev/null
+++ b/wqflask/wqflask/marker_regression/exceptions.py
@@ -0,0 +1,13 @@
+"""Mapping Exception classes."""
+
+class NoMappingResultsError(Exception):
+    "Exception to raise if no results are computed."
+
+    def __init__(self, trait, dataset, mapping_method):
+        self.trait = trait
+        self.dataset = dataset
+        self.mapping_method = mapping_method
+        self.message = (
+            f"The mapping of trait '{trait}' from dataset '{dataset}' using "
+            f"the '{mapping_method}' mapping method returned no results.")
+        super().__init__(self.message, trait, mapping_method)
diff --git a/wqflask/wqflask/templates/mapping_error.html b/wqflask/wqflask/templates/mapping_error.html
index 963bf7d6..8364af3c 100644
--- a/wqflask/wqflask/templates/mapping_error.html
+++ b/wqflask/wqflask/templates/mapping_error.html
@@ -9,7 +9,12 @@
     {%if error:%}
     <p>
       The following error was raised<br /><br />
-      &nbsp;&nbsp;&nbsp;&nbsp;{{error.args[0]}}<br /><br />
+      <dl>
+	<dt>Error message</dt>
+	<dd>{{error.args[0]}}</dd>
+	<dt>Error Type</dt>
+	<dd>{{error_type}}</dd>
+      </dl>
     </p>
     <p>
       Please contact Zach Sloan (zachary.a.sloan@gmail.com) or Arthur Centeno
diff --git a/wqflask/wqflask/views.py b/wqflask/wqflask/views.py
index ee0cd582..88dd31ba 100644
--- a/wqflask/wqflask/views.py
+++ b/wqflask/wqflask/views.py
@@ -46,6 +46,7 @@ from wqflask.external_tools import send_to_webgestalt
 from wqflask.external_tools import send_to_geneweaver
 from wqflask.comparison_bar_chart import comparison_bar_chart
 from wqflask.marker_regression import run_mapping
+from wqflask.marker_regression.exceptions import NoMappingResultsError
 from wqflask.marker_regression import display_mapping_results
 from wqflask.network_graph import network_graph
 from wqflask.correlation.show_corr_results import set_template_vars
@@ -720,10 +721,11 @@ def mapping_results_page():
         try:
             template_vars = run_mapping.RunMapping(start_vars, temp_uuid)
             if template_vars.no_results:
-                rendered_template = render_template("mapping_error.html")
-                return rendered_template
-        except FileNotFoundError as fnfe:
-            rendered_template = render_template("mapping_error.html", error=fnfe)
+                raise NoMappingResultsError(
+                    start_vars["trait_id"], start_vars["dataset"], start_vars["method"])
+        except Exception as exc:
+            rendered_template = render_template(
+                "mapping_error.html", error=exc, error_type=type(exc).__name__)
             return rendered_template
 
         if not template_vars.pair_scan: