Fix bulk_create not setting M2M on FK-related objects

model_bakery/baker.py

@@ -10,6 +10,7 @@
 
 from django.apps import apps
 from django.conf import settings
+from django.core.exceptions import FieldDoesNotExist
 from django.db.models import (
     AutoField,
     BooleanField,
@@ -915,7 +916,7 @@
                 setattr(objects[i], fk.name, fk_obj)
 
 
 def bulk_create(baker: Baker[M], quantity: int, **kwargs) -> list[M]:
     """
     Bulk create entries and all related FKs as well.
 
@@ -971,4 +972,37 @@
                         kwargs[reverse_relation_name]
                     )
 
+    # set many-to-many relations on FK-related objects specified via double-underscore
+    # syntax (e.g. home__dogs=[dog]). During prepare() the M2M values are stored in
+    # the sub-baker's m2m_dict but _handle_m2m() is never called because commit=False.
+    # _save_related_objs() only persists FK objects without touching M2M, so we must
+    # apply them here after all entries have been bulk-created and FK objects saved.
+    for kwarg_key, kwarg_value in kwargs.items():
+        if "__" not in kwarg_key:
+            continue
+        fk_field_name, m2m_field_name = kwarg_key.split("__", 1)
+        if "__" in m2m_field_name:
+            continue  # only handle one level of nesting
+        try:
+            fk_field = baker.model._meta.get_field(fk_field_name)
+        except FieldDoesNotExist:
+            continue
+        if not isinstance(fk_field, (ForeignKey, OneToOneField)):
+            continue
+        try:
+            related_m2m = fk_field.related_model._meta.get_field(m2m_field_name)
+        except FieldDoesNotExist:
+            continue
+        if not isinstance(related_m2m, ManyToManyField):
+            continue
+        # skip custom through models — .set() requires an auto-created through table;
+        # custom through models have extra required fields baker cannot populate here
+        through_model = related_m2m.remote_field.through
+        if not through_model._meta.auto_created:
+            continue
+        for entry in created_entries:
+            fk_obj = getattr(entry, fk_field_name, None)
+            if fk_obj is not None:
+                getattr(fk_obj, m2m_field_name).set(kwarg_value)
+
     return created_entries

tests/generic/models.py

@@ -182,6 +182,10 @@ class Home(models.Model):
     dogs = models.ManyToManyField("Dog")
 
 
+class HomeOwner(models.Model):
+    home = models.ForeignKey(Home, on_delete=models.CASCADE)
+
+
 class LonelyPerson(models.Model):
     only_friend = models.OneToOneField(Person, on_delete=models.CASCADE)
 

tests/test_baker.py

@@ -1255,6 +1255,22 @@ def test_make_should_create_objects_using_reverse_name(self):
             list(s1.classroom_set.all()) == list(s2.classroom_set.all()) == [classroom]
         )
 
+    @pytest.mark.django_db
+    def test_create_through_foreign_key_field(self):
+        """Regression test for M2M fields on FK-related objects with _bulk_create=True.
+
+        When a M2M value is specified via double-underscore lookup (e.g. home__dogs=[dog]),
+        baker must apply that M2M relationship to the saved FK object after bulk_create
+        completes. Previously, the M2M was stored in the sub-baker's m2m_dict during
+        prepare() but was never applied because _handle_m2m() is gated behind commit=True,
+        and _save_related_objs() only persists FK rows without touching M2M.
+        """
+        dog = baker.make(models.Dog)
+        baker.make(models.HomeOwner, home__dogs=[dog], _quantity=10, _bulk_create=True)
+
+        h1, h2 = models.HomeOwner.objects.all()[:2]
+        assert list(h1.home.dogs.all()) == list(h2.home.dogs.all()) == [dog]
+
 
 class TestBakerSeeded:
     @pytest.fixture