#35078: Incorrect order of migration operations when a new FK is added and is
part
of constraints as well
-------------------------------------+-------------------------------------
Reporter: Arpit | Owner: nobody
Goel |
Type: Bug | Status: new
Component: | Version: 4.2
Migrations | Keywords: migration
Severity: Normal | operations order
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 1
UI/UX: 0 |
-------------------------------------+-------------------------------------
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.
--
Ticket URL: <https://code.djangoproject.com/ticket/35078>
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