#30269: AlterField in database_operations of SeparateDatabaseAndState migration
doesn't set NOT NULL constraint for PostgreSQL
--------------------------------------+------------------------
Reporter: Dmitrii | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 2.1
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
--------------------------------------+------------------------
For changing a field, and not having some unpredictable behavior we employ
multi-stage deployments.
So for example we have a field:
{{{
name = models.CharField(max_length=255, null=True)
}}}
And we want to make it non-nullable. To make it so we perform two
migrations, firstly the state:
{{{
operations = [
# Plus whatever data migration is needed for the NULL values
migrations.SeparateDatabaseAndState(
state_operations=[
migrations.AlterField(
model_name='testmodel',
name='name',
field=models.CharField(max_length=255)
)
]
)
]
}}}
After all parts of the system have been updated with code that handles the
given field only in a non-nullable way, we can safely set it to NON NULL
in the database:
{{{
operations = [
migrations.SeparateDatabaseAndState(
database_operations=[
migrations.AlterField(
model_name='testmodel',
name='name',
field=models.CharField(max_length=255)
)
]
)
]
}}}
But the last migration doesn't actually perform any changes, the field
remains nullable in the database. This can be circumvented by using
migrations.RunSQL, but one can easily miss out the need to do that.
PostgreSQL in use: 9.6 official docker image.
Originally found for Django 1.8, reproduced for Django 2.1.7.
Didn't reproduce with SQLite.
--
Ticket URL: <https://code.djangoproject.com/ticket/30269>
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