Fix for None values in prefetch when fk_id==0

CHANGELOG.rst

@@ -20,6 +20,7 @@ Fixed
 - Fixed connection to `Oracle` database by adding database info to DBQ in connection string.
 - Fixed ORA-01435 error while using `Oracle` database (#1155)
 - Fixed processing of `ssl` option in MySQL connection string.
+- Fix for prefetch_related with foreign key id == 0.
 
 0.19.1
 ------
@@ -1265,4 +1266,4 @@ Docs/examples:
 
       await Tournament.filter(
           events__name__in=['1', '3']
-      ).order_by('-events__participants__name').distinct()
+      ).order_by('-events__participants__name').distinct()

tests/test_relations.py

@@ -239,6 +239,13 @@ async def test_prefetch_related_fk(self):
         event2 = await Event.filter(name="Test").prefetch_related("tournament")
         self.assertEqual(event2[0].tournament, tournament)
 
+    async def test_prefetch_related_fk_id_zero(self):
+        tournament = await Tournament.create(id=0, name="New Tournament")
+        await Event.create(name="Test", tournament_id=tournament.id)
+
+        event2 = await Event.filter(name="Test").prefetch_related("tournament")
+        self.assertEqual(event2[0].tournament, tournament)
+
     async def test_prefetch_related_rfk(self):
         tournament = await Tournament.create(name="New Tournament")
         event = await Event.create(name="Test", tournament_id=tournament.id)

tortoise/backends/base/executor.py

@@ -511,7 +511,7 @@ async def _prefetch_direct_relation(
         related_objects_for_fetch: Dict[str, list] = {}
         relation_key_field = f"{field}_id"
         for instance in instance_list:
-            if getattr(instance, relation_key_field):
+            if getattr(instance, relation_key_field) is not None:
                 key = cast(RelationalField, instance._meta.fields_map[field]).to_field
                 if key not in related_objects_for_fetch:
                     related_objects_for_fetch[key] = []