Get ManyToOneRel fields (reverse FK) back to work (#300)

* Get ManyToOneRel fields (reverse FK) back to work

* Update changelog

* Run linter

* Grammar fix 1

Co-authored-by: Tim Klein <timjklein36@gmail.com>

* Grammar fix 2

Co-authored-by: Tim Klein <timjklein36@gmail.com>

* Code linter

Co-authored-by: Tim Klein <timjklein36@gmail.com>

CHANGELOG.md

@@ -15,10 +15,12 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Extend type hints in `model_bakery.recipe` module, make `Recipe` class generic [PR #292](https://github.com/model-bakers/model_bakery/pull/292)
 - Explicitly add _fill_optional parameters to baker.make and baker.prepare to aid IDE autocomplete function. [PR #264](https://github.com/model-bakers/model_bakery/pull/264)
 - Fixed errors with reverse M2M relationships [PR #299](https://github.com/model-bakers/model_bakery/pull/299)
+- Fixed errors with reverse M2O relationships [PR #300](https://github.com/model-bakers/model_bakery/pull/300)
 - Improve exception message for unknown field types [PR #301](https://github.com/model-bakers/model_bakery/pull/301)
 
 ### Removed
 
+
 ## [1.4.0](https://pypi.org/project/model-bakery/1.4.0/)
 
 ### Added

model_bakery/baker.py

@@ -606,7 +606,18 @@ def _handle_one_to_many(self, instance: Model, attrs: Dict[str, Any]):
             manager = getattr(instance, key)
 
             for value in values:
-                if not value.pk:
+                # Django will handle any operation to persist nested non-persisted FK because
+                # save doesn't do so and, thus, raises constraint errors. That's why save()
+                # only gets called if the object doesn't have a pk and also doesn't hold fk
+                # pointers.
+                fks = any(
+                    [
+                        fk
+                        for fk in value._meta.fields
+                        if isinstance(fk, ForeignKey) or isinstance(fk, OneToOneField)
+                    ]
+                )
+                if not value.pk and not fks:
                     value.save()
 
             try:

tests/generic/models.py

@@ -455,3 +455,20 @@ class NonStandardManager(models.Model):
     name = models.CharField(max_length=30)
 
     manager = models.Manager()
+
+
+# The followin models were added after issue 291
+# Since they don't hold much meaning, they are only numbered ones
+class Issue291Model1(models.Model):
+    pass
+
+
+class Issue291Model2(models.Model):
+    m2m_model_1 = models.ManyToManyField(Issue291Model1)
+
+
+class Issue291Model3(models.Model):
+    fk_model_2 = models.ForeignKey(
+        Issue291Model2, related_name="bazs", on_delete=models.CASCADE
+    )
+    name = models.CharField(max_length=32)

tests/test_baker.py

@@ -569,6 +569,22 @@ def test_field_lookup_for_related_field_does_not_work_with_prepare(self):
         assert not person.pk
         assert 0 == models.RelatedNamesModel.objects.count()
 
+    def test_ensure_reverse_fk_for_many_to_one_is_working(self):
+        """This is a regression test to make sure issue 291 is fixed"""
+        fk1, fk2 = baker.prepare(
+            models.Issue291Model3, fk_model_2=None, name="custom name", _quantity=2
+        )
+        obj = baker.make(
+            models.Issue291Model2,
+            m2m_model_1=[baker.make(models.Issue291Model1)],
+            bazs=[fk1, fk2],
+        )
+
+        assert obj.bazs.count() == 2
+        related_1, related_2 = obj.bazs.all()
+        assert related_1.name == "custom name"
+        assert related_2.name == "custom name"
+
 
 @pytest.mark.django_db
 class TestHandlingUnsupportedModels: