First approach.

Author: WaVEV

django_mongodb/compiler.py

@@ -277,7 +277,9 @@ def execute_sql(
         try:
             query = self.build_query(
                 # Avoid $project (columns=None) if unneeded.
-                columns if self.query.annotations or not self.query.default_cols else None
+                columns
+                if self.query.annotations or not self.query.default_cols or self.query.distinct
+                else None
             )
         except EmptyResultSet:
             return iter([]) if result_type == MULTI else None
@@ -378,7 +380,7 @@ def check_query(self):
                 raise NotSupportedError("QuerySet.datetimes() is not supported on MongoDB.")
             if "datefield" in self.query.annotations:
                 raise NotSupportedError("QuerySet.dates() is not supported on MongoDB.")
-            raise NotSupportedError("QuerySet.distinct() is not supported on MongoDB.")
+            # raise NotSupportedError("QuerySet.distinct() is not supported on MongoDB.")
         if self.query.extra:
             if any(key.startswith("_prefetch_related_") for key in self.query.extra):
                 raise NotSupportedError("QuerySet.prefetch_related() is not supported on MongoDB.")
@@ -397,6 +399,20 @@ def build_query(self, columns=None):
                 )
             query.combinator_pipeline = self.get_combinator_queries()
         else:
+            # If we query distinct
+            if self.query.distinct:
+                distinct_fields = self.get_project_fields(columns, force_expression=True)
+                if not query.aggregation_pipeline:
+                    query.aggregation_pipeline = []
+                query.aggregation_pipeline.extend(
+                    [
+                        {"$group": {"_id": distinct_fields}},
+                        {"$addFields": {key: f"$_id.{key}" for key in distinct_fields}},
+                    ]
+                )
+                if "_id" not in distinct_fields:
+                    query.aggregation_pipeline.append({"$unset": "_id"})
+
             query.project_fields = self.get_project_fields(columns, ordering_fields)
             # If columns is None, then get_project_fields() won't add
             # ordering_fields to $project. Use $addFields (extra_fields) instead.
@@ -767,7 +783,7 @@ def build_query(self, columns=None):
         # Avoid $project (columns=None) if unneeded.
         columns = (
             compiler.get_columns()
-            if compiler.query.annotations or not compiler.query.default_cols
+            if self.query.annotations or not self.query.default_cols or self.query.distinct
             else None
         )
         subquery = compiler.build_query(columns)

django_mongodb/features.py

@@ -273,7 +273,7 @@ def django_test_expected_failures(self):
             "timezones.tests.NewDatabaseTests.test_query_datetimes_in_other_timezone",
         },
         "QuerySet.distinct() is not supported.": {
-            "aggregation.tests.AggregateTestCase.test_sum_distinct_aggregate",
+            # "aggregation.tests.AggregateTestCase.test_sum_distinct_aggregate",
             "aggregation_regress.tests.AggregationTests.test_annotate_distinct_aggregate",
             "aggregation_regress.tests.AggregationTests.test_conditional_aggregate_on_complex_condition",
             "aggregation_regress.tests.AggregationTests.test_distinct_conditional_aggregate",