Fix aliasing issues.

Author: WaVEV

django_mongodb/compiler.py

@@ -459,12 +459,8 @@ def get_combinator_queries(self):
                         )
                     )
                 compiler_.pre_sql_setup()
-                # Standardize columns as main query required.
                 columns = compiler_.get_columns()
-                if self.query.values_select:
-                    _, exprs = zip(*columns, strict=True)
-                    columns = tuple(zip(main_query_fields, exprs, strict=True))
-                parts.append((compiler_.build_query(columns), compiler_.collection_name))
+                parts.append((compiler_.build_query(columns), compiler_, columns))
             except EmptyResultSet:
                 # Omit the empty queryset with UNION.
                 if self.query.combinator == "union":
@@ -473,24 +469,39 @@ def get_combinator_queries(self):
         # Raise EmptyResultSet if all the combinator queries are empty.
         if not parts:
             raise EmptyResultSet
-        combinator_pipeline = parts.pop(0)[0].get_pipeline()
-        for part, collection in parts:
-            combinator_pipeline.append(
-                {"$unionWith": {"coll": collection, "pipeline": part.get_pipeline()}}
-            )
-            if not self.query.combinator_all:
-                ids = {}
-                for alias, expr in main_query_columns:
-                    # Unfold foreign fields.
-                    if isinstance(expr, Col) and expr.alias != self.collection_name:
-                        ids[self._unfold_column(expr)] = expr.as_mql(self, self.connection)
-                    else:
-                        ids[alias] = f"${alias}"
-                combinator_pipeline.append({"$group": {"_id": ids}})
-                projected_fields = self._fold_columns(ids)
-                combinator_pipeline.append({"$addFields": projected_fields})
-                if "_id" not in projected_fields:
-                    combinator_pipeline.append({"$unset": "_id"})
+        combinator_pipeline = []
+        for part, compiler_, columns in parts:
+            inner_pipeline = part.get_pipeline()
+            # Standardize result fields.
+            fields = {}
+            # When a .count() is called, the main_query_field has length 1
+            # otherwise it has the same length as columns.
+            for alias, (ref, expr) in zip(main_query_fields, columns, strict=False):
+                if isinstance(expr, Col) and expr.alias != compiler_.collection_name:
+                    fields[expr.alias] = 1
+                else:
+                    fields[alias] = f"${ref}" if alias != ref else 1
+            inner_pipeline.append({"$project": fields})
+            # Combine query with the current combinator pipeline.
+            if combinator_pipeline:
+                combinator_pipeline.append(
+                    {"$unionWith": {"coll": compiler_.collection_name, "pipeline": inner_pipeline}}
+                )
+            else:
+                combinator_pipeline = inner_pipeline
+        if not self.query.combinator_all:
+            ids = {}
+            for alias, expr in main_query_columns:
+                # Unfold foreign fields.
+                if isinstance(expr, Col) and expr.alias != self.collection_name:
+                    ids[self._unfold_column(expr)] = expr.as_mql(self, self.connection)
+                else:
+                    ids[alias] = f"${alias}"
+            combinator_pipeline.append({"$group": {"_id": ids}})
+            projected_fields = self._fold_columns(ids)
+            combinator_pipeline.append({"$addFields": projected_fields})
+            if "_id" not in projected_fields:
+                combinator_pipeline.append({"$unset": "_id"})
         return combinator_pipeline
 
     def get_lookup_pipeline(self):

django_mongodb/features.py

@@ -254,6 +254,7 @@ def django_test_expected_failures(self):
         "Test assumes integer primary key.": {
             "db_functions.comparison.test_cast.CastTests.test_cast_to_integer_foreign_key",
             "model_fields.test_foreignkey.ForeignKeyTests.test_to_python",
+            "queries.test_qs_combinators.QuerySetSetOperationTests.test_order_raises_on_non_selected_column",
         },
         "Exists is not supported on MongoDB.": {
             "aggregation.test_filter_argument.FilteredAggregateTests.test_filtered_aggregate_on_exists",