# Trouble trying to replace the ForeignKey model

**URL:** <https://forum.djangoproject.com/t/trouble-trying-to-replace-the-foreignkey-model/7978>\
**Category:** Using Django\
**Created:** [May 20, 2021, 2:31pm UTC](https://forum.djangoproject.com/t/trouble-trying-to-replace-the-foreignkey-model/7978 "2021-05-20T14:31:34Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![MrCordeiro](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.djangoproject.com/mrcordeiro/32/785_2.png) [@MrCordeiro](https://forum.djangoproject.com/u/MrCordeiro)\
**Post date:** [May 20, 2021, 2:31pm UTC](https://forum.djangoproject.com/t/trouble-trying-to-replace-the-foreignkey-model/7978/1 "2021-05-20T14:31:34Z")

</div>

Just like the data migration example for the docs, I’ve recently realized my models setup made little sense. However, I’m having issues trying to change it.

I have a `User` model, a One-on-one `Profile` model and a `Team` model. Right now, Team has a FK to Profile (the field `leader`). I’m trying to switch it to the `User` model and save myself from adding `select_related("leader__user")`every single time 😛

**My current approach**

1. Rename old FK `leader_profile`
2. Create new FK `leader`
3. Use a data migration to backfill information
4. Delete `leader_profile`

So, in detail:

1. Rename old FK

```python
operations = [
    migrations.RenameField(
        model_name='team',
        old_name='leader',
        new_name='leader_profile',
    ),
]

```

1. Create new FK:

```auto
# models.py
leader_profile = models.ForeignKey(Profile)
leader = models.ForeignKey(User)

```

1. Data migration

```auto
# migration file
from django.db import migrations

def backfill_leader(apps, schema_editor):
    # We can't import the Team model directly as it may be a newer
    # version than this migration expects. We use the historical version.
    Team = apps.get_model("dashboard", "Team")
    for team in Team.objects.all():
        team.leader = team.leader_profile.user
        team.save()

class Migration(migrations.Migration):

    operations = [
        migrations.RunPython(backfill_leader, reverse_code=migrations.RunPython.noop),
    ]

```

1. Delete `leader_profile`

**My current issue:**

I’m running into a snag when trying this. The error I get is `django.db.utils.ProgrammingError: relation "app_team_leader_id_bd9f9f21" already exists` which is weird. I would think that renaming the field would also rename the automatic indexes. I saw there was a [ticket](https://code.djangoproject.com/ticket/28803) for something related, but I’m not sure that’s what affecting me.

How do I solve this?

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<div class="post-metadata">

**Author:** ![KenWhitesell](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.djangoproject.com/kenwhitesell/32/280_2.png) [@KenWhitesell](https://forum.djangoproject.com/u/KenWhitesell)\
**Post date:** [May 20, 2021, 3:00pm UTC](https://forum.djangoproject.com/t/trouble-trying-to-replace-the-foreignkey-model/7978/2 "2021-05-20T15:00:12Z")

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I think the issue here may be that you’re creating the new FK field using the same name as the old field name, and if you’re trying to run all three migrations at the same time, I can see where there might be some confusion.

I’d either try giving the new FK field a new name, running the migrations, then renaming the field back to `leader`, and running migrations again, or, doing as the ticket describes and adding a manual step to rename the index, or to drop the index and recreate it.

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<div class="post-metadata">

**Author:** ![MrCordeiro](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.djangoproject.com/mrcordeiro/32/785_2.png) [@MrCordeiro](https://forum.djangoproject.com/u/MrCordeiro)\
**Post date:** [May 20, 2021, 3:14pm UTC](https://forum.djangoproject.com/t/trouble-trying-to-replace-the-foreignkey-model/7978/3 "2021-05-20T15:14:45Z")

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Maybe dropping it makes more sense, since the plan is to delete the old field anyways.

I’m trying to run all this in one fell swoop as it might be easier to replicate on production. In fact, my goad was to have a single migration file too! (. ❛ ᴗ ❛.)

I’m guessing however that, since the index name was generated automatically by Django, it’s unlikely it will also be callec “app\_team\_leader\_id\_bd9f9f21” outside my local machine… is there a way to get the index name programmatically?

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<div class="post-metadata">

**Author:** ![KenWhitesell](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.djangoproject.com/kenwhitesell/32/280_2.png) [@KenWhitesell](https://forum.djangoproject.com/u/KenWhitesell)\
**Post date:** [May 20, 2021, 3:59pm UTC](https://forum.djangoproject.com/t/trouble-trying-to-replace-the-foreignkey-model/7978/4 "2021-05-20T15:59:09Z")

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Postgresql provides the ‘pg\_indexes’ view to show all indexes. You could query it and get all the indexes on a particular table, then find where that field appears in the definition of the index. You’d probably want to save those definitions to recreate the indexes after.