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
35078	Incorrect order of migration operations when a new FK is added and is part of constraints as well	Arpit Goel	nobody	"I had an existing model, say:

{{{
class A(models.Model):
    title = models.CharField(max_length=255)
    fk1 = models.ForeignKey(
        User, on_delete=models.CASCADE,
    )
}}}

I created a new model **B** and added an FK in model **A** such that either **fk1** or **fk2** must exist.

{{{
class B(models.Model):
    title = models.CharField(max_length=255)

class A(models.Model):
    title = models.CharField(max_length=255)
    fk1 = models.ForeignKey(
        User, on_delete=models.SET_NULL, null=True, blank=True
    )
    fk2 = models.ForeignKey(
        B, on_delete=models.SET_NULL, null=True, blank=True
    )
    class Meta:
        constraints = [CheckConstraint(check=Q(fk1__isnull=False) | Q(fk2__isnull=False), name=""null_check"")]
}}}

When I run the **makemigrations** command, I get the following migration:

{{{
class Migration(migrations.Migration):

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='B',
            fields=[
                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('title', models.CharField(max_length=255)),
            ],
        ),
        migrations.AlterField(
            model_name='a',
            name='fk1',
            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, to=settings.AUTH_USER_MODEL),
        ),
        
        migrations.AddConstraint(
            model_name='a',
            constraint=models.CheckConstraint(check=models.Q(('fk1__isnull', False), ('fk2__isnull', False), _connector='OR'), name='null_check'),
        ),
        migrations.AddField(
            model_name='a',
            name='fk2',
            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, to='b'),
        ),
    ]

}}}

Ideally, the **AddField** operation should be done before **AddConstraint**, or the operation would fail due to a non-existing field. This should be an easy fix I guess, just need to move constraint ops to the end of the list instead of FK being at the end.
For now, I'm fixing the migration manually to make it work.
"	Bug	closed	Migrations	4.2	Normal	duplicate	migration operations order		Unreviewed	0	0	0	0	0	0