id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
35367	Multi-field constraint are not correctly handled when a form has one field marked as read-only	David	nobody	"When a model defines a constraint which relates two or more fields and one of those field is excluded from the related model form the validation provide a false positive and then the form tries to store an invalid record on the database, raising an `IntegrityError`.

Here is a code sample which reflects the situation

{{{#!python
# models.py
from django.db import models
from django.forms import modelform_factory


class MyModel(models.Model):
    field_1 = models.IntegerField(null=True)
    field_2 = models.IntegerField()

    class Meta:
        constraints = [
            models.CheckConstraint(
                name=""mycheck"",
                check=models.Q(field_1__lt=models.F(""field_2"")) | models.Q(field_1__isnull=True),
            )
        ]  


# this is like it would be done in admin if 'field_1' is set a readonly
Form = modelform_factory(MyModel, fields=['field_2'], exclude=['field_1'])
# this is ok for validation: 10 < 20
instance = MyModel(field_1=10, field_2=20)
# this does not respect the constraint: 10 > 5
form_instance = Form({'field_2': 5}, instance=instance)
form.is_valid()
# > True
form.save()
# > IntegrityError
}}}


This is somehow similar and related to #12627


"	Bug	closed	Forms	4.2	Normal	wontfix			Unreviewed	0	0	0	0	0	0