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
28803	When renaming foreign key indexes don't get renamed which breaks next migrations	Jacek Bzdak	nobody	"Here is what I did. I have following models: 

{{{
class ReferencedModel(models.Model):
   pass


class SecondReferencedModel(models.Model):
   pass


class ReferenceeModel(models.Model):
  child = models.ForeignKey(ReferencedModel, default=None, on_delete=models.CASCADE)
}}}

I want to swichch ``ReferenceeModel.child`` to ``SecondReferencedModel``. 

I want to do it by: 

1) Renaming ``ReferenceeModel.child_old`` 
2) Adding ``ReferenceeModel.child`` that points to proper model
3) Some RunPython magic
4) Delete  ``ReferenceeModel.child_old`` 

Actual bug: 

{{{

class Migration(migrations.Migration):

    initial = True

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='ReferencedModel',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
            ],
        ),
        migrations.CreateModel(
            name='SecondReferencedModel',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
            ],
        ),
        migrations.CreateModel(
            name='ReferenceeModel',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('child', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='index_error.ReferencedModel')),
            ],
        ),
    ]

class Migration(migrations.Migration):

    dependencies = [
        ('index_error', '0001_initial'),
    ]

    operations = [
        migrations.RenameField(
            model_name='referenceemodel',
            old_name='child',
            new_name='child_copy',
        ),
    ]


class Migration(migrations.Migration):

    dependencies = [
        ('index_error', '0002_auto_20171116_1505'),
    ]

    operations = [
        migrations.AddField(
            model_name='referenceemodel',
            name='child',
            field=models.ForeignKey(default=None, on_delete=django.db.models.deletion.CASCADE, to='index_error.SecondReferencedModel'),
        ),
    ]

}}}

Third migration explodes with following error: 

{{{django.db.utils.ProgrammingError: relation ""index_error_referenceemodel_child_id_59ba6fc6"" already exist }}} 

Which is due to the 

1) Field `` child = models.ForeignKey(ReferencedModel, ...)`` generates postgresql index named ``index_error_referenceemodel_child_id_59ba6fc6``
2) RenameField operation doesn't update index name (but changes field name)
3) When I try to create new field index names clash. 

My setup: 

* Django 1.11 (also broken in 2.0)
* postgresql database


"	Bug	closed	Migrations	1.11	Normal	duplicate			Unreviewed	0	0	0	0	0	0