#31317: Migration using CreateModel with unique_together followed by
AlterUniqueTogether crashes
-------------------------------------------------+------------------------
Reporter: Adam (Chainz) Johnson | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: master
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 |
-------------------------------------------------+------------------------
Full project to reproduce: https://github.com/adamchainz/django-unique-
together-bug
When squashing migrations I ended up with a migration that added a model
with `unique_together`, then altered the unique_together later:
{{{
migrations.CreateModel(
name="Book",
fields=[
(
"id",
models.AutoField(
auto_created=True,
primary_key=True,
serialize=False,
verbose_name="ID",
),
),
("title", models.CharField(default="", max_length=100)),
],
options={"unique_together": {("title",)},},
),
# ...
migrations.AlterUniqueTogether(
name="book", unique_together={("title", "author")},
),
}}}
This can crash when using `sqlmigrate` or `migrate` (see repo) with:
{{{
File "/.../django/django/db/backends/base/schema.py", line 380, in
alter_unique_together
self._delete_composed_index(model, fields, {'unique': True},
self.sql_delete_unique)
File "/.../django/django/db/backends/base/schema.py", line 414, in
_delete_composed_index
", ".join(columns),
ValueError: Found wrong number (0) of constraints for testapp_book(title)
}}}
This is because `_delete_composed_index` from `AlterUniqueTogehter` tries
to find the existing constraint name from the database.. But it hasn't
been created yet, so it could never be found - its SQL is sitting in
`deferred_sql`.
--
Ticket URL: <https://code.djangoproject.com/ticket/31317>
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