#25530: Deferred foreign keys operations fail when the column is changed during
the
same migration
------------------------------+--------------------
Reporter: simonphilips | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.8
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
------------------------------+--------------------
Possibly related to #25521
The following migration is the result of squashing 3 smaller migrations
together:
1. the initial migration
2. some random RunPython migration
3. changing the foreign key's column migration
The second step is only necessary to prevent squashmigrations from being
smart which avoids the issue.
The squashed migration (both optimized and unoptimized) looks as
following:
{{{#!python
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import migrations, models
# bug.migrations.0002_run_python
def do_something(apps, schema_editor):
pass # Do nothing, it's not important anyway.
class Migration(migrations.Migration):
replaces = [('bug', '0001_initial'), ('bug', '0002_run_python'),
('bug', '0003_change_db_column')]
dependencies = [
]
operations = [
migrations.CreateModel(
name='Child',
fields=[
('id', models.AutoField(auto_created=True,
serialize=False, verbose_name='ID', primary_key=True)),
('data', models.IntegerField(default=0)),
],
),
migrations.CreateModel(
name='Parent',
fields=[
('id', models.AutoField(auto_created=True,
serialize=False, verbose_name='ID', primary_key=True)),
('data', models.IntegerField(default=0)),
],
),
migrations.AddField(
model_name='child',
name='parent',
field=models.ForeignKey(db_column='my_parent',
to='bug.Parent'),
),
migrations.RunPython(
code=do_something,
),
migrations.AlterField(
model_name='child',
name='parent',
field=models.ForeignKey(to='bug.Parent'),
),
]
}}}
The models are:
{{{#!python
class Parent(models.Model):
data = models.IntegerField(default=0)
class Child(models.Model):
# Original db_column:
# parent = models.ForeignKey(Parent, db_column="my_parent")
# New db_column:
parent = models.ForeignKey(Parent)
data = models.IntegerField(default=0)
}}}
This will result in the following PostgreSQL error:
{{{
2015-10-08 15:00:27 CEST ERROR: column "my_parent" does not exist
2015-10-08 15:00:27 CEST STATEMENT: CREATE INDEX "bug_child_1e28668d" ON
"bug_child" ("my_parent")
}}}
The reason seems to be that any foreign key operations are added in SQL
format to the `schema_editor.deferred_sql` list and are then executed
after all other SQL commands. However, the third operation already renamed
the column for that index to 'parent_id'.
The deferred statements should follow any changes made during further
operations. Or, if that's not possible, perhaps some sort of 'insert
deferred statements now' operation could be added after each
'submigration' in the squashed migration?
Note that in this sample app it already crashes at the `CREATE INDEX`
statement, but the statement after that is `ALTER TABLE "bug_child" ADD
CONSTRAINT "bug_child_my_parent_3b5bc08e1603165f_fk_bug_parent_id" FOREIGN
KEY ("my_parent") REFERENCES "bug_parent" ("id") DEFERRABLE INITIALLY
DEFERRED`. I think the same issue might occur if `bug_parent(id)` would be
renamed or removed.
--
Ticket URL: <https://code.djangoproject.com/ticket/25530>
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