edits

Author: timgraham

django_mongodb/compiler.py

@@ -31,8 +31,8 @@ class SQLCompiler(compiler.SQLCompiler):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.aggregation_pipeline = None
-        # Dictionary mapping parent variable names to their corresponding indices.
-        self.column_mapping = {}
+        # Map columns to their subquery indices.
+        self.column_indices = {}
         # A list of OrderBy objects for this query.
         self.order_by_objs = None
         self.subqueries = []
@@ -160,14 +160,12 @@ def _prepare_annotations_for_aggregation_pipeline(self, order_by):
         return group, replacements
 
     def _get_group_expressions(self, order_by):
-        # The query.group_by is either None (no GROUP BY at all), True
-        # (group by select fields), or a list of expressions to be added
-        # to the group by.
         if self.query.group_by is None:
             return []
         seen = set()
         expressions = set()
         if self.query.group_by is not True:
+            # If group_by isn't True, then it's a list of expressions.
             for expr in self.query.group_by:
                 if not hasattr(expr, "as_sql"):
                     expr = self.query.resolve_ref(expr)
@@ -257,10 +255,10 @@ def pre_sql_setup(self, with_col_aliases=False):
                 having = self.having.replace_expressions(all_replacements).as_mql(
                     self, self.connection
                 )
-                # Add having subqueries.
+                # Add HAVING subqueries.
                 for query in self.subqueries or ():
                     pipeline.extend(query.get_pipeline())
-                # Clean added subqueries.
+                # Remove the added subqueries.
                 self.subqueries = []
                 pipeline.append({"$match": {"$expr": having}})
             self.aggregation_pipeline = pipeline
@@ -685,7 +683,9 @@ def execute_sql(self, result_type=MULTI):
     def check_query(self):
         super().check_query()
         if not self.single_alias:
-            raise NotSupportedError("Cannot use QuerySet.delete() when a subquery is required.")
+            raise NotSupportedError(
+                "Cannot use QuerySet.delete() when querying across multiple collections on MongoDB."
+            )
 
     def get_where(self):
         return self.query.where

django_mongodb/expressions.py

@@ -51,17 +51,17 @@ def case(self, compiler, connection):
 
 
 def col(self, compiler, connection):  # noqa: ARG001
-    # If the column is part of a subquery and belongs to one of the parent queries,
-    # it will be stored for reference using $let in a $lookup stage.
+    # If the column is part of a subquery and belongs to one of the parent
+    # queries, it will be stored for reference using $let in a $lookup stage.
     if (
         self.alias not in compiler.query.alias_refcount
         or compiler.query.alias_refcount[self.alias] == 0
     ):
         try:
-            index = compiler.column_mapping[self]
+            index = compiler.column_indices[self]
         except KeyError:
-            index = len(compiler.column_mapping)
-            compiler.column_mapping[self] = index
+            index = len(compiler.column_indices)
+            compiler.column_indices[self] = index
         return f"$${compiler.PARENT_FIELD_TEMPLATE.format(index)}"
     # Add the column's collection's alias for columns in joined collections.
     prefix = f"{self.alias}." if self.alias != compiler.collection_name else ""
@@ -106,18 +106,19 @@ def query(self, compiler, connection, lookup_name=None):
     from_table = next(
         e.table_name for alias, e in self.alias_map.items() if self.alias_refcount[alias]
     )
-    # To perform a subquery, a $lookup stage is added.
-    # This stage encapsulates the entire subquery pipeline within a $lookup operation.
-    # The "let" clause defines the variables needed to bridge the main collection with the subquery.
+    # To perform a subquery, a $lookup stage that escapsulates the entire
+    # subquery pipeline is added. The "let" clause defines the variables
+    # needed to bridge the main collection with the subquery.
     subquery.subquery_lookup = {
         "as": table_output,
         "from": from_table,
         "let": {
             compiler.PARENT_FIELD_TEMPLATE.format(i): col.as_mql(compiler, connection)
-            for col, i in subquery_compiler.column_mapping.items()
+            for col, i in subquery_compiler.column_indices.items()
         },
     }
-    # The result must be a list of values. The output is compressed with an aggregation pipeline.
+    # The result must be a list of values. The output is compressed with an
+    # aggregation pipeline.
     if lookup_name in ("in", "range"):
         if subquery.aggregation_pipeline is None:
             subquery.aggregation_pipeline = []
@@ -154,7 +155,7 @@ def query(self, compiler, connection, lookup_name=None):
                 },
             ]
         )
-        # Erase all the projection given that we already project the required value.
+        # Erase project_fields since the required value is projected above.
         subquery.project_fields = None
     compiler.subqueries.append(subquery)
     return f"${table_output}.{field_name}"

django_mongodb/features.py

@@ -92,17 +92,17 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "schema.tests.SchemaTests.test_composed_constraint_with_fk",
         "schema.tests.SchemaTests.test_remove_ignored_unique_constraint_not_create_fk_index",
         "schema.tests.SchemaTests.test_unique_constraint",
-        # Handle column default value.
-        # https://github.com/mongodb-labs/django-mongodb/issues/155
+        # 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.
+        # 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",
         "queries.test_qs_combinators.QuerySetSetOperationTests.test_union_in_subquery",
         "queries.test_qs_combinators.QuerySetSetOperationTests.test_union_in_with_ordering",
-        # ObjectId type mismatch in a subquery (casted as string).
-        # TODO: Create a ticket.
+        # ObjectId type mismatch in a subquery:
+        # https://github.com/mongodb-labs/django-mongodb/issues/161
         "queries.tests.RelatedLookupTypeTests.test_values_queryset_lookup",
         "queries.tests.ValuesSubqueryTests.test_values_in_subquery",
     }
@@ -218,9 +218,9 @@ def django_test_expected_failures(self):
         },
         "Test assumes integer primary key.": {
             "db_functions.comparison.test_cast.CastTests.test_cast_to_integer_foreign_key",
+            "expressions.tests.BasicExpressionsTests.test_nested_subquery_outer_ref_with_autofield",
             "model_fields.test_foreignkey.ForeignKeyTests.test_to_python",
             "queries.test_qs_combinators.QuerySetSetOperationTests.test_order_raises_on_non_selected_column",
-            "expressions.tests.BasicExpressionsTests.test_nested_subquery_outer_ref_with_autofield",
         },
         "Cannot use QuerySet.delete() when querying across multiple collections on MongoDB.": {
             "delete.tests.FastDeleteTests.test_fast_delete_aggregation",
@@ -233,6 +233,16 @@ def django_test_expected_failures(self):
             "delete_regress.tests.Ticket19102Tests.test_ticket_19102_select_related",
             "one_to_one.tests.OneToOneTests.test_o2o_primary_key_delete",
         },
+        "Cannot use QuerySet.delete() when a subquery is required.": {
+            "delete_regress.tests.DeleteTests.test_self_reference_with_through_m2m_at_second_level",
+            "many_to_many.tests.ManyToManyTests.test_assign",
+            "many_to_many.tests.ManyToManyTests.test_assign_ids",
+            "many_to_many.tests.ManyToManyTests.test_clear",
+            "many_to_many.tests.ManyToManyTests.test_remove",
+            "many_to_many.tests.ManyToManyTests.test_reverse_assign_with_queryset",
+            "many_to_many.tests.ManyToManyTests.test_set",
+            "many_to_many.tests.ManyToManyTests.test_set_existing_different_type",
+        },
         "Cannot use QuerySet.update() when querying across multiple collections on MongoDB.": {
             "expressions.tests.BasicExpressionsTests.test_filter_with_join",
             "queries.tests.Queries4Tests.test_ticket7095",
@@ -337,16 +347,6 @@ def django_test_expected_failures(self):
             "schema.tests.SchemaTests.test_rename_column_renames_deferred_sql_references",
             "schema.tests.SchemaTests.test_rename_table_renames_deferred_sql_references",
         },
-        "Cannot use QuerySet.delete() when a subquery is required.": {
-            "delete_regress.tests.DeleteTests.test_self_reference_with_through_m2m_at_second_level",
-            "many_to_many.tests.ManyToManyTests.test_assign",
-            "many_to_many.tests.ManyToManyTests.test_assign_ids",
-            "many_to_many.tests.ManyToManyTests.test_clear",
-            "many_to_many.tests.ManyToManyTests.test_remove",
-            "many_to_many.tests.ManyToManyTests.test_reverse_assign_with_queryset",
-            "many_to_many.tests.ManyToManyTests.test_set",
-            "many_to_many.tests.ManyToManyTests.test_set_existing_different_type",
-        },
         "Test executes raw SQL.": {
             "aggregation.tests.AggregateTestCase.test_coalesced_empty_result_set",
             "aggregation_regress.tests.AggregationTests.test_annotate_with_extra",

django_mongodb/query.py

@@ -56,7 +56,8 @@ def __init__(self, compiler):
         self.aggregation_pipeline = compiler.aggregation_pipeline
         self.extra_fields = None
         self.combinator_pipeline = None
-        # Stage that encapsulates the pipeline for performing a nested subquery within a $lookup.
+        # $lookup stage that encapsulates the pipeline for performing a nested
+        # subquery.
         self.subquery_lookup = None
 
     def __repr__(self):

django_mongodb/query_utils.py

@@ -34,8 +34,9 @@ def process_rhs(node, compiler, connection):
             value = rhs.as_mql(compiler, connection)
     else:
         _, value = node.process_rhs(compiler, connection)
+        lookup_name = node.lookup_name
         # Undo Lookup.get_db_prep_lookup() putting params in a list.
-        if node.lookup_name not in ("in", "range"):
+        if lookup_name not in ("in", "range"):
             value = value[0]
     if hasattr(node, "prep_lookup_value_mongo"):
         value = node.prep_lookup_value_mongo(value)