Opened 4 years ago

Closed 4 years ago

Last modified 4 years ago

#23091 closed Bug (fixed)

Squashed migrations may try to add existing constraint if there was RunPython between create and alter some-model migrations

Reported by: anonymous Owned by: Andrew Godwin
Component: Migrations Version: 1.7-rc-1
Severity: Release blocker Keywords:
Cc: Triage Stage: Accepted
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no


I squashed a lot of migrations, some with RunPython functions. The squashed migration needed some fixing to work. At some point of the squashed migration there was a "CreateModel" operation that created some model with relation to User:

('user', models.ForeignKey(blank=True, to_field='id', to=settings.AUTH_USER_MODEL, null=True)),

But as the models got edited there was a migration (rather pointless, caused by editable=False):

field=models.ForeignKey(blank=True, null=True, to_field='id', to=settings.AUTH_USER_MODEL, editable=False),

In between there was a RunPython which quite likely prevented squashing those two migrations into one. Running such migrations ended up with:

 File "/var/www/buku/virtualenvs/1405079302/lib/python3.4/site-packages/django/db/backends/", line 66, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: constraint "buku_vendor_offerredir_user_id_75e4400f46095260_fk_auth_user_id" for relation "buku_vendor_offerredirect" already exists

The SQL it was trying to run was:

ALTER TABLE "buku_vendor_offerredirect" ADD CONSTRAINT buku_vendor_offerredir_user_id_75e4400f46095260_fk_auth_user_id FOREIGN KEY ("user_id") REFERENCES "auth_user" ("id") DEFERRABLE INITIALLY DEFERRED []

It would be handy if that "self.cursor.execute(sql, params)" from django/db/backends/ also printed the SQL it was trying to run so it would be easier to find the operation in migration (or make exception more verbose).

I had like 4 such cases. Some quite serious like removing null=True and adding unique=True

Change History (8)

comment:1 Changed 4 years ago by Piotr Maliński

comment:2 Changed 4 years ago by Tim Graham

I am not exactly clear on what the problem is (the duplicate constraint and/or the issue about SQL being printed -- if these are separate issues they belong in separate tickets). It would be quite helpful if you could add a test for Django's test suite that demonstrates the issue. Without that, it may be difficult to reproduce the issue unless you provide the minimal steps to reproduce it.

comment:3 Changed 4 years ago by Piotr Maliński

The problem is with the constraint being re-added. I'll try to provide a migration flow to reproduce it.

comment:4 Changed 4 years ago by Piotr Maliński

Steps to reproduce:

  • create model like:
class Foo(models.Model):
    user = models.ForeignKey('auth.User')
  • make migrations and migrate
  • create empty migration and use RunPython that will have a function (can be blank) for example:
def foo(apps, schema_editor):

  • migrate it and then edit the model to for example (change to a field with constraint):
class Foo(models.Model):
    user = models.ForeignKey('auth.User', editable=False)
  • makemigrations and migrate the change
  • squash migrations
  • try running tests so that squashed migration will be applied to a clean database. You should get a django.db.utils.ProgrammingError - constraint exists.

comment:5 Changed 4 years ago by Tim Graham

Severity: NormalRelease blocker
Triage Stage: UnreviewedAccepted
Type: UncategorizedBug

Thanks, I could reproduce this using PostgreSQL but not SQLite (no FK support there yet per #14204).

comment:6 Changed 4 years ago by Andrew Godwin

Owner: changed from nobody to Andrew Godwin
Status: newassigned

This is reproduceable without the RunPython stuff - you just need to run the operations sequentially:

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.db import models, migrations
from django.conf import settings

def foo(apps, schema_editor):

class Migration(migrations.Migration):

    dependencies = [

    operations = [
                ('id', models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True)),
                ('user', models.ForeignKey(to=settings.AUTH_USER_MODEL)),
            field=models.ForeignKey(editable=False, to=settings.AUTH_USER_MODEL),

comment:7 Changed 4 years ago by Andrew Godwin <andrew@…>

Resolution: fixed
Status: assignedclosed

In c06e124b5e73bd99c6ec563c64fd50d6a45457d8:

Fixed #23091: CreateModel and AddField were clashing with deferred SQL

comment:8 Changed 4 years ago by Andrew Godwin <andrew@…>

In a918c60c378b575ca52ebcfae977056b8bc5a4de:

[1.7.x] Fixed #23091: CreateModel and AddField were clashing with deferred SQL

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