#25577: Squashed migrations do not work if deletion of indexed field can't be
optimized on postgresql database
----------------------------+--------------------
Reporter: jbzdak | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.8
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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I have following model:
{{{
class AModel(models.Model):
indexed_field = models.CharField(max_length=200, db_index=True)
}}}
And three migrations:
1. First one creates this model
2. Second one runs a custom sql (this SQL is empty in my example, but it
could for example copy contents of ``indexed_field`` column to another
column)
3. Third one deletes indexed field from the model
If I run these three migrations separately they work.
If I squash these migrations into one they stop working with following
error:
{{{
File "/home/jb/programs/django-migrations-issue/venv/lib/python3.5/site-
packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: column "indexed_field" does not exist
}}}
My guess is this error is because:
Index creation executed as a ``deferred_sql`` statement, which is executed
at the end of migration. At the end of my squashed migration there is no
``indexed_field`` column on the table, and postgresql raises error.
It works when migrations are separate because index creation is executed
at the end of migration. It works on squashed migrations without RunSQL
migration in between because field creation is entirely optimized.
I have attached example project, if you try to migrate it, it will
explode. If you remove squashed migration it will work.
--
Ticket URL: <https://code.djangoproject.com/ticket/25577>
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