fix backlink serialization when link data is fetched

Author: alexdlukens

beanie/odm/fields.py

@@ -516,6 +516,12 @@ def __modify_schema__(cls, field_schema: Dict[str, Any]):
                 }
             )
 
+        @staticmethod
+        def serialize(value: Union[Link[T], BaseModel]):
+            if isinstance(value, Link):
+                return value.to_dict()
+            return value.dict()
+
     def to_ref(self):
         return self.ref
 
@@ -524,7 +530,7 @@ def to_dict(self):
 
 
 if not IS_PYDANTIC_V2:
-    ENCODERS_BY_TYPE[Link] = lambda o: o.to_dict()
+    ENCODERS_BY_TYPE[Link] = lambda o: o.serialize()
 
 
 class BackLink(Generic[T]):
@@ -535,6 +541,12 @@ def __init__(self, document_class: Type[T]):
 
     if IS_PYDANTIC_V2:
 
+        @staticmethod
+        def serialize(value: Union[BackLink[T], BaseModel]):
+            if isinstance(value, BackLink):
+                return value.to_dict()
+            return value.model_dump(mode="json")
+
         @classmethod
         def wrapped_validate(
             cls, source_type: Type[Any], handler: GetCoreSchemaHandler
@@ -565,7 +577,7 @@ def __get_pydantic_core_schema__(
                     values_schema=core_schema.any_schema(),
                 ),
                 serialization=core_schema.plain_serializer_function_ser_schema(
-                    lambda instance: cls.to_dict(instance),
+                    lambda instance: cls.serialize(instance),
                     return_schema=core_schema.dict_schema(),
                     when_used="json-unless-none",
                 ),
@@ -610,13 +622,19 @@ def __modify_schema__(cls, field_schema: Dict[str, Any]):
                 }
             )
 
+        @staticmethod
+        def serialize(value: Union[BackLink[T], BaseModel]):
+            if isinstance(value, BackLink):
+                return value.to_dict()
+            return value.dict()
+
     def to_dict(self) -> dict[str, str]:
         document_class = DocsRegistry.evaluate_fr(self.document_class)  # type: ignore
         return {"collection": document_class.get_collection_name()}
 
 
 if not IS_PYDANTIC_V2:
-    ENCODERS_BY_TYPE[BackLink] = lambda o: o.to_dict()
+    ENCODERS_BY_TYPE[BackLink] = lambda o: o.serialize()
 
 
 class IndexModelField:

tests/fastapi/routes.py

@@ -71,3 +71,8 @@ async def create_house_new(house: House = Body(...)):
     await house.save(link_rule=WriteRules.WRITE)
     await house.sync()
     return house
+
+
+@house_router.get("/person/{id}", response_model=Person)
+async def get_person(id: PydanticObjectId):
+    return await Person.get(id, fetch_links=True, nesting_depth=1)

tests/fastapi/test_api.py

@@ -66,3 +66,22 @@ async def test_create_house_new(api_client):
     assert resp_json["name"] == payload["name"]
     assert resp_json["owner"]["name"] == payload["owner"]["name"][-3:]
     assert resp_json["owner"]["house"]["collection"] == "House"
+
+
+async def test_get_person(api_client):
+    payload = {
+        "name": "FreshHouse",
+        "owner": {"name": "will_be_overridden_to_Bob"},
+    }
+    resp = await api_client.post("/v1/house", json=payload)
+    resp_json = resp.json()
+
+    person_id = resp_json["owner"].get("id")
+    if person_id is None:
+        person_id = resp_json["owner"].get("_id")
+    assert person_id is not None
+
+    resp2 = await api_client.get(f"/v1/person/{person_id}")
+
+    resp2_json = resp2.json()
+    assert resp2_json["name"] == payload["owner"]["name"][-3:]