simplify adding relations

orm/fields/foreign_key.py

@@ -1,4 +1,4 @@
-from typing import Type, List, Any, Union, TYPE_CHECKING
+from typing import Type, List, Any, Union, TYPE_CHECKING, Optional
 
 import sqlalchemy
 from pydantic import BaseModel
@@ -12,9 +12,8 @@ if TYPE_CHECKING:  # pragma no cover
 
 
 def create_dummy_instance(fk: Type["Model"], pk: int = None) -> "Model":
-    init_dict = {fk.__pkname__: pk or -1}
     init_dict = {
-        **init_dict,
+        **{fk.__pkname__: pk or -1},
         **{
             k: create_dummy_instance(v.to)
             for k, v in fk.__model_fields__.items()
@@ -26,12 +25,12 @@ def create_dummy_instance(fk: Type["Model"], pk: int = None) -> "Model":
 
 class ForeignKey(BaseField):
     def __init__(
-        self,
-        to: Type["Model"],
-        name: str = None,
-        related_name: str = None,
-        nullable: bool = True,
-        virtual: bool = False,
+            self,
+            to: Type["Model"],
+            name: str = None,
+            related_name: str = None,
+            nullable: bool = True,
+            virtual: bool = False,
     ) -> None:
         super().__init__(nullable=nullable, name=name)
         self.virtual = virtual
@@ -51,8 +50,11 @@ class ForeignKey(BaseField):
         return to_column.get_column_type()
 
     def expand_relationship(
-        self, value: Any, child: "Model"
-    ) -> Union["Model", List["Model"]]:
+            self, value: Any, child: "Model"
+    ) -> Optional[Union["Model", List["Model"]]]:
+
+        if value is None:
+            return None
 
         if isinstance(value, orm.models.Model) and not isinstance(value, self.to):
             raise RelationshipInstanceError(
@@ -77,15 +79,10 @@ class ForeignKey(BaseField):
                 )
             model = create_dummy_instance(fk=self.to, pk=value)
 
-        self.add_to_relationship_registry(model, child)
-
-        return model
-
-    def add_to_relationship_registry(self, model: "Model", child: "Model") -> None:
         model._orm_relationship_manager.add_relation(
-            model.__class__.__name__.lower(),
-            child.__class__.__name__.lower(),
             model,
             child,
             virtual=self.virtual,
         )
+
+        return model

orm/relations.py

@@ -16,7 +16,7 @@ def get_table_alias() -> str:
 
 
 def get_relation_config(
-    relation_type: str, table_name: str, field: ForeignKey
+        relation_type: str, table_name: str, field: ForeignKey
 ) -> Dict[str, str]:
     alias = get_table_alias()
     config = {
@@ -37,7 +37,7 @@ class RelationshipManager:
         self._relations = dict()
 
     def add_relation_type(
-        self, relations_key: str, reverse_key: str, field: ForeignKey, table_name: str
+            self, relations_key: str, reverse_key: str, field: ForeignKey, table_name: str
     ) -> None:
         if relations_key not in self._relations:
             self._relations[relations_key] = get_relation_config(
@@ -56,15 +56,15 @@ class RelationshipManager:
                     del self._relations[rel_type][model._orm_id]
 
     def add_relation(
-        self,
-        parent_name: str,
-        child_name: str,
-        parent: "FakePydantic",
-        child: "FakePydantic",
-        virtual: bool = False,
+            self,
+            parent: "FakePydantic",
+            child: "FakePydantic",
+            virtual: bool = False,
     ) -> None:
         parent_id = parent._orm_id
         child_id = child._orm_id
+        parent_name = parent.get_name()
+        child_name = child.get_name()
         if virtual:
             child_name, parent_name = parent_name, child_name
             child_id, parent_id = parent_id, child_id
@@ -97,7 +97,7 @@ class RelationshipManager:
         return False
 
     def get(
-        self, relations_key: str, instance: "FakePydantic"
+            self, relations_key: str, instance: "FakePydantic"
     ) -> Union["Model", List["Model"]]:
         if relations_key in self._relations:
             if instance._orm_id in self._relations[relations_key]:
@@ -108,8 +108,8 @@ class RelationshipManager:
     def resolve_relation_join(self, from_table: str, to_table: str) -> str:
         for relation_name, relation in self._relations.items():
             if (
-                relation["source_table"] == from_table
-                and relation["target_table"] == to_table
+                    relation["source_table"] == from_table
+                    and relation["target_table"] == to_table
             ):
                 return self._relations[relation_name]["table_alias"]
         return ""

tests/test_foreign_keys.py

@@ -74,6 +74,13 @@ async def test_wrong_query_foreign_key_type():
         Track(title="The Error", album="wrong_pk_type")
 
 
+@pytest.mark.asyncio
+async def test_setting_explicitly_empty_relation():
+    async with database:
+        track = Track(album=None, title="The Bird", position=1)
+        assert track.album is None
+
+
 @pytest.mark.asyncio
 async def test_model_crud():
     async with database:
@@ -146,8 +153,8 @@ async def test_fk_filter():
 
         tracks = (
             await Track.objects.select_related("album")
-            .filter(album__name="Fantasies")
-            .all()
+                .filter(album__name="Fantasies")
+                .all()
         )
         assert len(tracks) == 3
         for track in tracks:
@@ -155,8 +162,8 @@ async def test_fk_filter():
 
         tracks = (
             await Track.objects.select_related("album")
-            .filter(album__name__icontains="fan")
-            .all()
+                .filter(album__name__icontains="fan")
+                .all()
         )
         assert len(tracks) == 3
         for track in tracks:
@@ -198,8 +205,8 @@ async def test_multiple_fk():
 
         members = (
             await Member.objects.select_related("team__org")
-            .filter(team__org__ident="ACME Ltd")
-            .all()
+                .filter(team__org__ident="ACME Ltd")
+                .all()
         )
         assert len(members) == 4
         for member in members:
@@ -218,8 +225,8 @@ async def test_pk_filter():
 
         tracks = (
             await Track.objects.select_related("album")
-            .filter(position=2, album__name="Test")
-            .all()
+                .filter(position=2, album__name="Test")
+                .all()
         )
         assert len(tracks) == 1