Rename operations should rename indexes, constraints, sequences and triggers named after their former value

[Chris Woytowitz]

This one's a bit of an edge case, but I ran into it trying to refactor some models on my moderately large work project.

Let's say I have a Django 1.7 app called sample:

1. Create a model Bar.
2. Create a model Foo with bar = models.ForeignKey(Bar, blank=True, null=True)
3. makemigrations (migration 0001)
4. Rename Foo to OldFoo.
5. makemigrations, say yes to the rename prompt (migration 0002)
6. Create new model Foo, which also has bar = models.ForeignKey(Bar, blank=True, null=True)
7. makemigrations (migration 0003)
8. migrate

When migrate hits 0003, it throws this error:
django.db.utils.OperationalError: index sample_foo_4350f7d0 already exists

You may notice that sqlmigrate sample 0001 and sqlmigrate sample 0003 have the same line in both of them:
CREATE INDEX sample_foo_4350f7d0 ON "sample_foo" ("bar_id");

In my production case, I actually had no problems on servers, because South had created the index with a different name. When I renamed the models and added a field, the new index did not collide with the old one. However, our test suite started failing, because it would run the migrations from the ground up, exposing the above bug.

I haven't decided on a workaround yet, but I thought I'd bring this to your attention. I might have to inject a migration that renames the index created in 0001, or something to that effect.

The attached test case has a project dj17test in the state after having performed all of the above steps.

[Chris Woytowitz]

It is worth noting that if you use postgres instead, the error is django.db.utils.ProgrammingError: relation "sample_foo_4350f7d0" already exists.

[Simon Charette]

Haven't reproduced but the issue seems legit from the report.

I guess the RenameModel operation should also rename indexes generated from the original model name.

[Tom V]

I've found an associated case where a field with db_index=True, is renamed, and another db_indexed field created with the original's name.

Just discussed this with @andrewgodwin, I've agreed to write a test case for the field rename case, and then post about a solution on django-dev, with his preference being to make index names randomised.

[Tom V]

I've added a schema test case: ​https://github.com/tomviner/django/compare/ticket_23577_with_tests

This should currently fail on all backends except sqlite (which doesn't rename fields - it drop/creates the whole table). When this bug is fixed, it should pass for all backends, for that reason I haven't added any unittest.skip decorator.

Edit: link to tests updated.

[Tom V]

After ​a discussion on django-dev it makes sense to leave the resolution of this issue to ​Marc Tamlyn's Advanced indexes DEP, which he says will involve user specified/reproducible index names, as well as index renaming.

[ris]

Replying to tomviner:

I've found an associated case where a field with db_index=True, is renamed, and another db_indexed field created with the original's name.

FWIW I have worked around this in my migrations by doing two AlterFields, dropping & re-creating the index by doing db_index=False then db_index=True.

[skyjur]

This also happens when renaming a ManyToManyField and then adding a new ManyToManyField with the same name. I've opened ticket #25752 then @timgraham pointed out that it's duplicate of this one.

[Ian Clark]

I tried to migrate to a new model and bumped into this one. To fix, I made sure that I renamed my existing model to "old" first (e.g. Model->ModelOld), create the new model with the previous name (e.g. Model), migrate the data and then remove the old model. My previous strategy of creating the new table migrating the data and then renaming it broke due to the index issues.

[Luke Murphy]

Replying to ris:

Replying to tomviner:

I've found an associated case where a field with db_index=True, is renamed, and another db_indexed field created with the original's name.

FWIW I have worked around this in my migrations by doing two AlterFields, dropping & re-creating the index by doing db_index=False then db_index=True.

Confirmed. This worked for me also. I can use manage.py sqlmigrate <app> <migration> to see which indexes are giving me conflicts (should be the same as the error you get when you try to run migrate) and then used the db_index=False/True trick with AlterField.

[Simon Charette]

#24528 was a duplicate.

[Simon Charette]

#24715 was duplicate with a patch for the Oracle case where the sequence and triggers created for an AutoField were not renamed.

[Simon Charette]

This should also be the case for AlterField operations on both sides (e.g. foreign key constraint names are generated from their referenced table and column names).

[Martin Koistinen]

Until this is resolved, one can work-around this issue by doing something like:

        migrations.RunSQL(
            'ALTER INDEX myapp_mymodel_myfield_othermodel_id_0f4cfc54 rename TO myapp_mymodel_myfield_othermodel_legacy_id_0f4cfc54',
            'ALTER INDEX myapp_mymodel_myfield_othermodel_legacy_id_0f4cfc54 rename TO myapp_mymodel_myfield_othermodel_id_0f4cfc54',
        )

This sort of approach should work well for both FKs and M2Ms (example below), but it may make your migrations DB Backend specific =/

[Tim Graham]

I closed #28803 as a duplicate.

[jonathan-golorry]

I just ran into this issue with RenameField on ManyToMany relations. The (automatically generated) through table changes name, but the id_seq for it doesn't.

[Thomas Riccardi]

Some analysis (with postgresql backend):

• when creating a new field with index (such as a ForeignKey), django creates the column and the index
• when deleting a field, django only deletes the column: it lets postgresql delete all related index automatically
• when renaming a field, django only renames the column: it lets postgresql update all index references (and probably more), *but does not* rename the index

It seems django doesn't really track the index name, and it works great except for renames

=> when a new index has to be created for the old field name, the index name conflicts: this is this issue.

This reliance on field reference automatic update by the db seems to create a similar issue with index_together/unique_together:
field rename + index_together/unique_together alternation to update the field name results in no SQL except the RENAME COLUMN: the index/unique names are *not* updated.

The workaround from comment 17 (ticket:23577#comment:17) with a manual index rename may create issues when this ticket is fixed:
at that point django will probably assume the index name is the one it generates if it had to create the index, and the comment uses a different one (the hash_suffix_part is different)
=> for more rubustness/future compatibility I suggest to use the "proper" index name: manually create migrations to delete then re-create the field, and use ./manage.py sqlmigrate to get the created index name (it depends solely on table name and index fields name: see django/db/backends/base/schema.py:BaseDatabaseSchemaEditor._create_index_name)

[Thomas Riccardi]

To get the proper new index name:

from django.db import connection
schema_editor = connection.schema_editor()

def get_index_name(field):
    return schema_editor._create_index_name(field.model._meta.db_table, [field.attname])

get_index_name(ModelFoo.field_bar.field)

[clavay]

I tried this and it works :
In the migration file I replace this :

        migrations.AlterField(
            model_name='foo',
            name='variable',
            field=models.ForeignKey(null=True, on_delete=django.db.models.deletion.SET_NULL, to='app.Variable'),
        ),

with this :

        migrations.RenameModel('Foo', 'FooNew'),
        migrations.AlterField(
            model_name='foonew',
            name='variable',
            field=models.ForeignKey(null=True, on_delete=django.db.models.deletion.SET_NULL, to='app.Variable'),
        ),
        migrations.RenameModel('FooNew', 'Foo'),

Is it a good solution ?

[Thomas Riccardi]

Restore ticket description

[Steve Recio]

Just ran into this issue when attempting to rename and rebuild a table. Renaming the table doesn't change any of the indexes or constraints so I can't rebuild another table with the same ManyToMany relationship. I tried creating a through table and renaming the foreign keys but that doesn't seem to do it either as the "UNIQUE TOGETHER" index name itself never changes.

[Jef D]

Just opened this issue: https://code.djangoproject.com/ticket/33488#ticket which was apparently a duplicate of this one. I did a rename and quickly after I reused the old name of the field which made this very visible. However, I can imagine that it is a difficult error to find when it happens with longer periods in between. The longer a project lasts, the more likely it is that one will run into this kind of issues.

Unfortunately, the issue doesn't seem to have a high priority given that it has been 7 years since it was opened. For now I will sandwich the rename migration with unsetting and setting the index in two additional migrations.

[scholtalbers]

Encountered this (django 3.2) when trying to add a field with the same name of a field I renamed in a few migrations before. The original index is still existing. It should have been renamed as part of the AlterField migration.

[Mikko Ahonen]

Ran into this as well, using django 3.1 and Postgres. Similar case as for scholtalbers.

I wanted to switch to using a library that wanted to add field to model which was conflicting with the existing name, used for similar purpose (parent).

I renamed the field (to old_parent), ran migration, created migration, added the library (which added the parent field), created migration, run migration.

Locally migrations worked because I was using SQLite, but when installing on staging it failed because of conflicting index name.

[John Zeller]

Also ran into this same issue the way the OP wrote it

[Steven Mapes]

So I ended up created a duplicate of this ticket for issue #34647 and I had a look at Clavay's suggestion but one of the issues here is that Django then detects the change in future migrations, at least if you rename the name and the db_table) and then it puts it back into a broken state as the SQL migrations that are generated are still wrong. So the work around needs to be run as raw SQL in order to bypass Django knowing about it.

[Roberto Maurizzi]

Just hit the same problem after renaming a Model and creating a new one with the old name (to conform to how several other models in that application ended up being named).

I was able to fix it by:

• changing the new Model creation in the migration to specify spatial_index=False (it was a GIS field, I guess for regular ones you need to use db_index=False)
• running makemigrations again: since I never changed the models, it detected the missing indexes and created another migration that added them to the db

This worked both for migrating the production database (was working earlier too) and when running tests.

[Fabian Pottbäcker]

I just ran into a similar Issue when reverting migrations on Postgres, specifically I have the following condensed and abstracted migration history:

1. Setup:
   1. Create model Author
   2. Create model Book (author = ForeignKey(Author))
2. Introduce PenNames
   1. Create model PenName
   2. Alter Book.author to allow null
   3. Add author_new = ForgeignKey(PenName, null=True) to book
   4. RunPython to create PenNames for all authors and set author_new accordingly (including a corresponding reverse operation)
   5. Drop Book.author
   6. Alter Book.author_new to prohibit null
   7. Rename Book.author_new to Book.author
3. Remove PenNames (for whatever reason)
   1. Some Operation to repopulate Book.author
   2. Drop column Book.author

After successfully applying these migrations, reverting to State 1 will error when undoing step 2.5, since the index book_author_id... was already created when undoing step 3.2, but it would be called book_author_new_id... when applying these migrations forwards.

[Victor Rocha]

I am at DjangoCon US sprints trying to get to the bottom of this

[yardensachs]

I encountered this issue when renaming models on Postgres. There are several indexes that need to be addressed. I'm not sure how to proceed.
I assume I can use the SQL operation, but that does not work well in SQLITE.