use class from self.__class__ if document_class does not exist

This is the case when BackLink data has been fetched using fetch_links=True

Author: alexdlukens

beanie/odm/fields.py

@@ -611,7 +611,9 @@ def __modify_schema__(cls, field_schema: Dict[str, Any]):
             )
 
     def to_dict(self) -> dict[str, str]:
-        document_class = DocsRegistry.evaluate_fr(self.document_class)  # type: ignore
+        document_class = DocsRegistry.evaluate_fr(
+            getattr(self, "document_class", self.__class__)
+        )
         return {"collection": document_class.get_collection_name()}
 
 

tests/odm/test_beanie_object_dumping.py

@@ -1,9 +1,13 @@
 import pytest
 from pydantic import BaseModel, Field
 
-from beanie import Link, PydanticObjectId
+from beanie import BackLink, Link, PydanticObjectId
 from beanie.odm.utils.pydantic import IS_PYDANTIC_V2
-from tests.odm.models import DocumentTestModelWithSoftDelete
+from tests.odm.models import (
+    DocumentTestModelWithSoftDelete,
+    DocumentWithBackLink,
+    DocumentWithLink,
+)
 
 
 class TestModel(BaseModel):
@@ -20,6 +24,17 @@ def data_maker():
     )
 
 
+def data_maker_backlink_pair():
+    back_link_doc = DocumentWithBackLink(
+        id="5f4e3f3b7c0c9d001f7d4c8e",
+        back_link=BackLink(document_class=DocumentWithLink),
+    )
+    link_doc = DocumentWithLink(
+        id="5f4e3f3b7c0c9d001f7d4c8f", link=back_link_doc
+    )
+    return link_doc, back_link_doc
+
+
 @pytest.mark.skipif(
     not IS_PYDANTIC_V2,
     reason="model dumping support is more complete with pydantic v2",
@@ -38,3 +53,18 @@ def test_id_types_serialized_when_dumping_to_json():
     dumped = data_maker().model_dump(mode="json")
     assert isinstance(dumped["my_id"], str)
     assert isinstance(dumped["fake_doc"]["id"], str)
+
+
+@pytest.mark.skipif(
+    not IS_PYDANTIC_V2,
+    reason="model dumping support is more complete with pydantic v2",
+)
+def test_backlink_serialization_to_json_when_fetched():
+    link_doc, back_link_doc = data_maker_backlink_pair()
+
+    # presume we have fetched this BackLink by using fetch_links=True, nesting_depth=1
+    back_link_doc.back_link = link_doc
+
+    dumped_model = back_link_doc.model_dump(mode="json")
+
+    assert dumped_model["back_link"] == {"collection": "DocumentWithLink"}

tests/odm/test_relations.py

@@ -614,6 +614,24 @@ async def test_with_chaining_aggregation(self):
 
         assert addresses_count[0] == {"count": 10}
 
+    @pytest.mark.skipif(
+        not IS_PYDANTIC_V2,
+        reason="model dumping support is more complete with pydantic v2",
+    )
+    async def test_dump_model_with_fetched_backlink(
+        self, link_and_backlink_doc_pair
+    ):
+        link_doc, back_link_doc = link_and_backlink_doc_pair
+
+        document_with_fetched_backlinks = await DocumentWithBackLink.get(
+            back_link_doc.id, fetch_links=True, nesting_depth=1
+        )
+
+        assert document_with_fetched_backlinks is not None
+        model_json = document_with_fetched_backlinks.model_dump(mode="json")
+
+        assert model_json["back_link"] == {"collection": "DocumentWithLink"}
+
     async def test_with_chaining_aggregation_and_text_search(self):
         # ARRANGE
         NUM_DOCS = 10