edits

Author: timgraham

django_mongodb/compiler.py

@@ -85,8 +85,9 @@ def _make_result(self, entity, columns, converters, tuple_expected=False):
             field = col.field
             column_alias = getattr(col, "alias", None)
             obj = (
+                # Use the related object...
                 entity.get(column_alias, {})
-                # Does this column refer to an object for select_related()?
+                # ...if this column refers to an object for select_related().
                 if column_alias is not None and column_alias != self.collection_name
                 else entity
             )

django_mongodb/expressions.py

@@ -43,6 +43,7 @@ def case(self, compiler, connection):
 
 
 def col(self, compiler, connection):  # noqa: ARG001
+    # Add the column's collection's alias for columns in joined collections.
     prefix = f"{self.alias}." if self.alias != compiler.collection_name else ""
     return f"${prefix}{self.target.column}"
 

django_mongodb/features.py

@@ -78,7 +78,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "model_fields.test_jsonfield.TestQuerying.test_order_grouping_custom_decoder",
         "model_fields.test_jsonfield.TestQuerying.test_ordering_by_transform",
         "model_fields.test_jsonfield.TestQuerying.test_ordering_grouping_by_key_transform",
-        # DecimalField lookup with F expressoin crashes:
+        # DecimalField lookup with F expression crashes:
         # decimal.InvalidOperation: [<class 'decimal.ConversionSyntax'>]
         "lookup.tests.LookupTests.test_lookup_rhs",
         # Wrong results in queries with multiple tables.
@@ -228,8 +228,8 @@ def django_test_expected_failures(self):
             "expressions_case.tests.CaseExpressionTests.test_filter_with_aggregation_in_value",
             "expressions_case.tests.CaseExpressionTests.test_m2m_exclude",
             "expressions_case.tests.CaseExpressionTests.test_m2m_reuse",
-            "lookup.tests.LookupQueryingTests.test_aggregate_combined_lookup",
             "lookup.test_decimalfield.DecimalFieldLookupTests",
+            "lookup.tests.LookupQueryingTests.test_aggregate_combined_lookup",
             "from_db_value.tests.FromDBValueTest.test_aggregation",
             "timezones.tests.LegacyDatabaseTests.test_query_aggregation",
             "timezones.tests.LegacyDatabaseTests.test_query_annotation",

django_mongodb/query.py

@@ -42,8 +42,8 @@ def __init__(self, compiler, columns):
         self.columns = columns
         self._negated = False
         self.ordering = []
-        self.collection_name = self.compiler.collection_name
         self.collection = self.compiler.get_collection()
+        self.collection_name = self.compiler.collection_name
         self.mongo_query = getattr(compiler.query, "raw_query", {})
         self.lookup_pipeline = None
 
@@ -137,6 +137,7 @@ def join(self, compiler, connection):
     join_fields = self.join_fields or self.join_cols
     lhs_fields = []
     rhs_fields = []
+    # Add a join condition for each pair of joining fields.
     for lhs, rhs in join_fields:
         if isinstance(lhs, str):
             lhs_mql = lhs
@@ -159,16 +160,20 @@ def join(self, compiler, connection):
             "$lookup": {
                 # The right-hand table to join.
                 "from": self.table_name,
-                # Define the current pipeline variables to be used in the match
-                # expression of the pipeline.
+                # The pipeline variables to be matched in the pipeline's
+                # expression.
                 "let": {
                     f"{parent_template}{i}": parent_field
                     for i, parent_field in enumerate(lhs_fields)
                 },
                 "pipeline": [
                     {
-                        # Match all the conditions: self.table_name.field1 = parent_table.field1
-                        # and self.table_name.field2 = parent_table.field2 and ...
+                        # Match the conditions:
+                        #   self.table_name.field1 = parent_table.field1
+                        # AND
+                        #   self.table_name.field2 = parent_table.field2
+                        # AND
+                        #   ...
                         "$match": {
                             "$expr": {
                                 "$and": [
@@ -184,13 +189,11 @@ def join(self, compiler, connection):
             }
         },
     ]
-
-    # To avoid missing data when using the unwind operator,
-    # an empty collection should be added if the join is not an inner join.
-    # For inner joins, rows with empty arrays are removed,
-    # as the unwind operator unrolls or unnests the array and removes the row if it is empty.
-    # This is the expected behavior for inner joins.
-    # However, for left outer joins (LOUTER), an empty collection is returned instead.
+    # To avoid missing data when using $unwind, an empty collection is added if
+    # the join isn't an inner join. For inner joins, rows with empty arrays are
+    # removed, as $unwind unrolls or unnests the array and removes the row if
+    # it's empty. This is the expected behavior for inner joins. For left outer
+    # joins (LOUTER), however, an empty collection is returned.
     if self.join_type != INNER:
         lookup_pipeline.append(
             {