[Django] #34128: django re-using the name of a squashed migration leads to CircularDependencyError

Django

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Oct 31, 2022, 9:14:13 AM10/31/22

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I've squashed two migrations, creating this file:
```
# Generated by Django 3.2 on 2022-10-30 14:15

from django.db import migrations, models

class Migration(migrations.Migration):

replaces = [('api', '0005_achievement_difficulty'), ('api',
'0006_alter_achievement_difficulty')]

dependencies = [
('api',
'0004_achievement_squashed_0005_alter_achievement_submission'),
]

operations = [
migrations.AddField(
model_name='achievement',
name='difficulty',
field=models.SmallIntegerField(default=0),
),
]
```

After rolling out the change, I've deleted 0005_achievement_difficulty and
0006_alter_achievement_difficulty.

Now I've did some more changes to the model, causing django to create the
following 0006_alter_achievement_difficulty:
```
# Generated by Django 3.2 on 2022-10-31 12:59

from django.db import migrations, models

class Migration(migrations.Migration):

dependencies = [
('api',
'0005_achievement_difficulty_squashed_0006_alter_achievement_difficulty'),
]

operations = [
migrations.AlterField(
model_name='achievement',
name='difficulty',
field=models.SmallIntegerField(),
),
]
```

Which leads to the following error:
```
File "/usr/local/lib/python3.10/site-
packages/django/db/migrations/graph.py", line 274, in ensure_not_cyclic
raise CircularDependencyError(", ".join("%s.%s" % n for n in cycle))
django.db.migrations.exceptions.CircularDependencyError:
api.0005_achievement_difficulty_squashed_0006_alter_achievement_difficulty
```

Renaming the migration file to 0006_alter_achievement_difficulty_new.py
fixed it.

While I wouldn't rule out a mistake on my side, it seems the way django
creates the migration name can lead to new migrations being named like
squashed and removed ones, causing the dependency check to wrongfully
assume the squashed migration would depend on it.

--
Ticket URL: <https://code.djangoproject.com/ticket/34128>
Django <https://code.djangoproject.com/>
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Django

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Oct 31, 2022, 9:15:17 AM10/31/22

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#34128: django re-using the name of a squashed migration leads to
CircularDependencyError
-------------------------------------+-------------------------------------

Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------

Description changed by discordianfish:

Old description:

New description:

Hi,

class Migration(migrations.Migration):

--

--
Ticket URL: <https://code.djangoproject.com/ticket/34128#comment:1>

Django

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Nov 1, 2022, 1:32:53 AM11/1/22

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#34128: django re-using the name of a squashed migration leads to
CircularDependencyError
-------------------------------------+-------------------------------------

Reporter: Johannes 'fish' | Owner: nobody
Ziemke |
Type: Uncategorized | Status: closed

Component: Database layer | Version: 3.2
(models, ORM) |

Severity: Normal | Resolution: invalid

Changes (by Mariusz Felisiak):

* status: new => closed
* resolution: => invalid

Comment:

Thanks for this ticket, however transition of the squashed migration to a
normal migration is more complicated and requires removing the `replaces`
attribute, see [https://docs.djangoproject.com/en/dev/topics/migrations
/#squashing-migrations docs]:

> You must then transition the squashed migration to a normal migration
> - Deleting all the migration files it replaces.
> - Updating all migrations that depend on the deleted migrations to
depend on the squashed migration instead
> - **Removing the `replaces` attribute in the `Migration` class of the
squashed migration (this is how Django tells that it is a squashed
migration).**

--
Ticket URL: <https://code.djangoproject.com/ticket/34128#comment:2>

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