#34084: Regression in Django 4.1 so ModelForms always set self.instance even when none passed in -------------------------------------+------------------------------------- Reporter: Steven | Owner: nobody Mapes | Type: Bug | Status: new Component: Database | Version: 4.1 layer (models, ORM) | Severity: Normal | Keywords: modelform Triage Stage: | Has patch: 0 Unreviewed | Needs documentation: 0 | Needs tests: 0 Patch needs improvement: 0 | Easy pickings: 0 UI/UX: 0 | -------------------------------------+------------------------------------- I came across this bug this morning when running my testsuite against Django 3.2, 4.0 and 4.1 (4.1.0, 4.1.1 and 4.1.2). The issue is with ModelForms when they are used without passing in an existing saved instance. I thought this was related to the regression that was then fixed in 4.1.2 and mentioned in both [https://code.djangoproject.com/ticket/33984 33984] and [https://code.djangoproject.com/ticket/33952 33952] but the issue is still occurring even though both of those are closed.
To test you can use the below models, form and unit test {{{ # models.py from django.db import models class Tag(models.Model): tag = models.SlugField(max_length=64, unique=True) class Thing(models.Model): tag = models.ForeignKey(Tag, on_delete=models.CASCADE, related_name="things") active = models.BooleanField(default=True) }}} {{{ # forms.py from django import forms from example.models import Tag class TagForm(forms.ModelForm): class Meta: model = Tag fields = ["tag"] def __init__(self, *args, **kwargs): super(TagForm, self).__init__(*args, **kwargs) if self.instance and self.instance.things: inactive_things = self.instance.things.filter(active=False) # Do something with it }}} {{{ from unittest.case import TestCase from example.forms import TagForm class TagFormCase(TestCase): def test_required(self): """Test required fields""" form = TagForm({}) self.assertFalse(form.is_valid()) self.assertEqual( { "tag": ["This field is required."], }, form.errors, ) }}} If you run the test on Django versions <4.1 including Django 2.*, Django 3.* and 4.0.* then it'll pass but on 4.1.* it'll fail with ```ValueError: 'Tag' instance needs to have a primary key value before this relationship can be used.``` In order to pass the if statement needs to be changed to ```if self.instance.pk and self.instance.things``` as self.instance is no longer None if no instance is passed in. If your model uses a custom primary key such as a uuid4 then it'll work as expected as the uuid4 is already called -- Ticket URL: <https://code.djangoproject.com/ticket/34084> Django <https://code.djangoproject.com/> The Web framework for perfectionists with deadlines. -- You received this message because you are subscribed to the Google Groups "Django updates" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-updates+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/django-updates/01070183c81702f2-5fb61ab4-7aed-428b-ad2e-9690f2f36400-000000%40eu-central-1.amazonses.com.