Readme

Minimal project to show a possible bug in Django.

It seems like that UniqueConstraint with condition are not checked in a BaseInlineFormSet.

The important bits are:

• The models.py file, in particular the unique_design_type constraint:

  class Product(models.Model):
      design = models.ForeignKey(...)
      type = models.CharField(...)
      size = models.CharField(null=True, ...)
      ...
  
      class Meta:
              constraints = [
              models.UniqueConstraint(
                  fields=["design", "type"],
                  condition=models.Q(size__isnull=True),
                  name="unique_design_type",
              ),
              ...
          ]

• The tests.py file, in particular the TestFormSetValidation.test_validation_unique_design_type test case:

  def test_validation_unique_design_type(self):
      ...
  
      formset = FormSet(
          data={
              f"{prefix}-TOTAL_FORMS": "2",
              f"{prefix}-MAX_NUM_FORMS": "1000",
              f"{prefix}-0-type": "Mug",
              f"{prefix}-0-price": "2",
              f"{prefix}-1-type": "Mug",
              f"{prefix}-1-price": "2",
          },
          instance=design,
      )
  
      # EXPECTED BEHAVIOR
      self.assertFalse(formset.is_valid())
      with self.assertRaisesMessage(ValueError, "didn't validate"):
          formset.save()
  
      # ACTUAL BEHAVIOR
      # self.assertTrue(formset.is_valid())
      # with self.assertRaisesMessage(IntegrityError, "UNIQUE constraint failed"):
      #     formset.save()

Note how the validation don't catch the UniqueConstraint violation, which gives an IntegrityError instead.

In tests.py, there are also tests to confirm that the constraint behaves correctly in all the other cases, as long as a constraint without condition which works as expected.

Installation

python -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

./manage.py test