#34898: Adding non-deterministic collations to unique CharFields crashes on
PostgreSQL.
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Reporter: Mariusz Felisiak | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 4.2
Severity: Normal | Resolution:
Keywords: PostgreSQL collation | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Tom Carrick):
Interesting. I looked into it and it is indeed only this case that breaks.
If you add them both at once, it's fine. If you add the collation, then
the unique, it's fine. But if it's unique, then you try to add the
collation, boom.
As you might expect, this also happens for `db_index`.
However, it doesn't happen when using `Meta` `indexes` / `constraints`
unless you have `opclasses=["varchar_pattern_ops"]`, and if you remove
this in the same migration as adding the collation, this also seems to
work fine (I'm not sure if by luck of because Django first removes the
constrain, then does other stuff, then adds the constraint purposefully).
Given that `db_index` is discouraged in the docs... and I'd make the same
argument for doing the same for `unique=True`, maybe a note in the docs
about this is enough?
I didn't look very hard to find a solution, but I think it should be
possible by adding stuff to
`django.db.backends.postgresql.schema.DatabaseSchemaEditor._alter_field`.
I'll take a look.
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Ticket URL: <https://code.djangoproject.com/ticket/34898#comment:1>
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