#34366: Migration optimizer does not reduce multiple AlterField
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Reporter: Laurent Tramoy | Owner: nobody
Type: Uncategorized | Status: new
Component: Migrations | Version: 4.1
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 |
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Let's consider the following operations:
{{{
operations = [
migrations.AddField(
model_name="book",
name="title",
field=models.CharField(max_length=256, null=True),
),
migrations.AlterField(
model_name="book",
name="title",
field=models.CharField(max_length=128, null=True),
),
migrations.AlterField(
model_name="book",
name="title",
field=models.CharField(max_length=128, null=True,
help_text="help"),
),
migrations.AlterField(
model_name="book",
name="title",
field=models.CharField(max_length=128, null=True,
help_text="help", default=None),
),
]
}}}
If I run the optimizer, I get only the `AddField`, as we could expect.
However, if the `AddField` model is separated from the AlterField (e.g.
because of a non-elidable migration, or inside a non-squashed migration),
none of the `AlterField` are reduced:
{{{
optimizer.optimize(operations[1:], "books")
[<AlterField model_name='book', name='title',
field=<django.db.models.fields.CharField>>,
<AlterField model_name='book', name='title',
field=<django.db.models.fields.CharField>>,
<AlterField model_name='book', name='title',
field=<django.db.models.fields.CharField>>]
}}}
Indeed, the `AlterField.reduce` does not consider the the case where
`operation` is also an `AlterField`.
Is this behaviour intended? If so, could it be documented?
Otherwise, would it make sense to add something like
{{{
if isinstance(operation, AlterField) and
self.is_same_field_operation(
operation
):
return [operation]
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/34366>
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