Fix #397 -- Prevent related() from creating duplicate parents (#563)

Author: amureki

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 
 ### Changed
+- Fix `related()` with FK relations creating duplicate parent entities ([#397](https://github.com/model-bakers/model_bakery/issues/397))
 
 ### Removed
 

model_bakery/baker.py

@@ -658,11 +658,26 @@ def _handle_auto_now(self, instance: Model, attrs: dict[str, Any]):
             setattr(instance, k, v)
 
     def _handle_one_to_many(self, instance: Model, attrs: dict[str, Any]):
+        """Handle reverse one-to-many relationships.
+
+        For related() callables, automatically injects the parent instance
+        to the FK field to avoid duplicate creation via foreign_key() in child recipes.
+        """
+        import types
+
+        from .recipe import related
+
         for key, values in attrs.items():
             manager = getattr(instance, key)
 
             if callable(values):
-                values = values()
+                if isinstance(values, types.MethodType) and isinstance(
+                    values.__self__, related
+                ):
+                    fk_field_name = manager.field.name
+                    values = values(**{fk_field_name: instance})
+                else:
+                    values = values()
 
             for value in values:
                 # Django will handle any operation to persist nested non-persisted FK because

model_bakery/recipe.py

@@ -244,6 +244,6 @@ def __init__(self, *args: str | Recipe[M]) -> None:
             else:
                 raise TypeError("Not a recipe")
 
-    def make(self) -> list[M | list[M]]:
+    def make(self, **attrs: Any) -> list[M | list[M]]:
         """Persist objects to m2m relation."""
-        return [m.make() for m in self.related]
+        return [m.make(**attrs) for m in self.related]

tests/test_recipes.py

@@ -441,6 +441,20 @@ def test_related_models_recipes(self):
         assert lady.dog_set.all()[0].breed == "Pug"
         assert lady.dog_set.all()[1].breed == "Basset"
 
+    def test_related_fk_does_not_create_duplicate_parent(self):
+        """Regression test for issue #397.
+
+        When using related() with FK, the parent should be reused,
+        not duplicated by the child recipe's foreign_key().
+        """
+        from tests.generic.models import Person
+
+        lady = baker.make_recipe("tests.generic.dog_lady")
+        assert Person.objects.count() == 1
+        assert lady.dog_set.count() == 2
+        for dog in lady.dog_set.all():
+            assert dog.owner == lady
+
     def test_related_models_recipes_make_mutiple(self):
         ladies = baker.make_recipe("tests.generic.dog_lady", _quantity=2)
         assert ladies[0].dog_set.count() == 2