add support for expression default value when it raises EmptyResultSet

Author: WaVEV

django_mongodb/compiler.py

@@ -550,7 +550,11 @@ def get_project_fields(self, columns=None, ordering=None, force_expression=False
                     else expr.as_mql(self, self.connection)
                 )
             except EmptyResultSet:
-                fields[collection][name] = Value(False).as_mql(self, self.connection)
+                empty_result_set_value = getattr(expr, "empty_result_set_value", NotImplemented)
+                value = (
+                    False if empty_result_set_value is NotImplemented else empty_result_set_value
+                )
+                fields[collection][name] = Value(value).as_mql(self, self.connection)
             except FullResultSet:
                 fields[collection][name] = Value(True).as_mql(self, self.connection)
         # Annotations (stored in None) and the main collection's fields

django_mongodb/features.py

@@ -73,10 +73,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "backends.tests.ThreadTests.test_pass_connection_between_threads",
         "backends.tests.ThreadTests.test_closing_non_shared_connections",
         "backends.tests.ThreadTests.test_default_connection_thread_local",
-        # Column default values aren't handled when a field raises
-        # EmptyResultSet: https://github.com/mongodb-labs/django-mongodb/issues/155
-        "annotations.tests.NonAggregateAnnotationTestCase.test_empty_queryset_annotation",
-        "db_functions.comparison.test_coalesce.CoalesceTests.test_empty_queryset",
         # Union as subquery is not mapping the parent parameter and collections:
         # https://github.com/mongodb-labs/django-mongodb/issues/156
         "queries.test_qs_combinators.QuerySetSetOperationTests.test_union_in_subquery_related_outerref",