#28438: Initial migration creates fields not listed in the migration if mixin
class
changes
-----------------------------------------+------------------------
Reporter: Michal Dabski | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.11
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-----------------------------------------+------------------------
Consider the sample model with a mixin class:
{{{
from django.db import models
class TestMixin(object):
pass
class TestModel(TestMixin, models.Model):
sample_field = models.CharField(max_length=20)
}}}
When running makemigrations, django creates a perfectly good and valid
migration:
{{{
# -*- coding: utf-8 -*-
# Generated by Django 1.11.3 on 2017-07-26 17:03
from __future__ import unicode_literals
from django.db import migrations, models
import migration_test.models
class Migration(migrations.Migration):
initial = True
dependencies = [
]
operations = [
migrations.CreateModel(
name='TestModel',
fields=[
('id', models.AutoField(auto_created=True,
primary_key=True, serialize=False, verbose_name='ID')),
('sample_field', models.CharField(max_length=20)),
],
bases=(migration_test.models.TestMixin, models.Model),
),
]
}}}
SQL:
{{{
BEGIN;
--
-- Create model TestModel
--
CREATE TABLE "migration_test_testmodel" ("id" serial NOT NULL PRIMARY KEY,
"sample_field" varchar(20) NOT NULL);
COMMIT;
}}}
Next, refactor mixin class to add a field to it - need to change mixin's
base class to {{{models.Model}}}, otherwise field will not be correctly
inherited by models:
{{{
class TestMixin(models.Model):
mixin_field = models.CharField(max_length=20, default='test')
class Meta:
abstract = True
}}}
Thie creates a new migration which adds {{{mixin_field}}} to it - nothing
special. However, when applying both migrations after the model changes,
second migration fails with the following error
{{{django.db.utils.ProgrammingError: column "mixin_field" of relation
"migration_test_testmodel" already exists}}}. as it turns out, the first
migration's SQL has now changed to include {{{mixin_field}}}:
{{{
BEGIN;
--
-- Create model TestModel
--
CREATE TABLE "migration_test_testmodel" ("id" serial NOT NULL PRIMARY KEY,
"mixin_field" varchar(20) NOT NULL, "sample_field" varchar(20) NOT NULL);
COMMIT;
}}}
The python code of the migration obviously has not changed, but the
resulting SQL did, and it includes a field not explicitly listed in the
migration's {{{fields}}}.
Note:
- this does not happen if the mixin class extends {{{models.Model}}} to
begin with.
- if model extends a mixin that extends {{{object}}}, it ends up in
model's {{{bases}}}, however if mixin extends {{{model.Model}}} it does
not.
Tested with Django 1.11.3, Python 2.7
--
Ticket URL: <https://code.djangoproject.com/ticket/28438>
Django <https://code.djangoproject.com/>
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