#33901: non-deterministic collations doesn't work with Unique=True on
Postgres13.3
-------------------------------------+-------------------------------------
Reporter: Ed Chai | Owner: Ed Chai
Type: Bug | Status: closed
Component: Migrations | Version: dev
Severity: Normal | Resolution: fixed
Keywords: collation unique | Triage Stage: Ready for
citext | checkin
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Ed Chai):
Replying to [comment:13 Petter Friberg]:
> Not sure if there should be a new ticket here or not but I'm still
seeing this on 4.2 when having a relation that points to a unique field
with a non-deterministic collation.
>
> For instance, consider if we run the following migration operation:
>
> {{{
> #!python
> migrations.CreateModel(
> name="ExtendedUser",
> fields=[
> ('id', models.BigAutoField(auto_created=True, primary_key=True,
serialize=False, verbose_name='ID')),
> ('user',
models.OneToOneField(on_delete=django.db.models.deletion.CASCADE,
to=settings.AUTH_USER_MODEL, to_field='username'))
> ]
> )
> }}}
>
> Running `manage.py sqlmigrate` for that operation displays the generated
`_like` index
>
> {{{
> #!sql
> BEGIN;
> --
> -- Create model ExtendedUser
> --
> CREATE TABLE "myapp_extendeduser" ("id" bigint NOT NULL PRIMARY KEY
GENERATED BY DEFAULT AS IDENTITY, "user_id" varchar(30) COLLATE "ci" NOT
NULL UNIQUE);
> ALTER TABLE "myapp_extendeduser" ADD CONSTRAINT
"myapp_extendeduser_user_id_<chars>_fk_myapp_user_username" FOREIGN KEY
("user_id") REFERENCES "myapp_user" ("username") DEFERRABLE INITIALLY
DEFERRED;
> CREATE INDEX "myapp_extendeduser_user_id_<chars>_like" ON
"myapp_extendeduser" ("user_id" varchar_pattern_ops);
> COMMIT;
> }}}
>
> (Not sure if there's more to it but) I think the
[https://code.djangoproject.com/changeset/f3f9d03edf17ccfa17263c7efa0b1350d1ac9278
provided patch] could be extended with something like below to resolve at
least `OneToOneField`
>
> {{{
> #!python
> # Non-deterministic collations on Postgresql don't support
indexes
> # for operator classes varchar_pattern_ops/text_pattern_ops.
> if getattr(field, "db_collation", None) or
(field.is_relation and getattr(field.target_field, "db_collation", None)):
> return None
> }}}
I think your code is not related to this issue. This ticket only
addresses errors that occur when both db_collation and unique are applied
on Postgres. `CREATE INDEX` is the expected operation when you create
foreign keys
--
Ticket URL: <https://code.djangoproject.com/ticket/33901#comment:15>
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