#35594: Add support for non-distinct NULL expressions to
UniqueConstraint.validate()
-------------------------------------+-------------------------------------
Reporter: Mark Gensler | Owner: (none)
Type: New feature | Status: new
Component: Database layer | Version: 5.0
(models, ORM) |
Severity: Normal | Resolution:
Keywords: uniqueconstraint | Triage Stage:
nulls_distinct | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Description changed by Mark Gensler:
Old description:
> Expressions which evaluate to `NULL` within
> `UniqueConstraint(*expressions, nulls_distinct=False)` are still treated
> as distinct by `UniqueConstraint.validate()`. This means a
> `ValidationError` is not raised when it should be.
>
> Similarly, if the database connection uses
> `interprets_empty_strings_as_nulls` this is also ignored by
> `.validate()`.
>
> Should #35575 be merged, this problem would also extend to any
> `GeneratedField` included in `UniqueConstraint(fields=[...],
> nulls_distinct=False)`.
>
> E.g.
>
> {{{
> class Book(models.Model):
> name = CharField(max_length=255, null=True)
>
> class Meta:
> constraints = [
> UniqueConstraint(F("name"), nulls_distinct=False,
> name="book_name_null_unique")
> ]
> }}}
> then
> {{{
> > Book.objects.create(name=None)
> > book = Book(name=None)
> > book.full_clean() # Should raise a `ValidationError` but doesn't.
> > book.save() # The database raises an `IntegrityError`.
> }}}
>
> This ticket was raised following discussion in
> https://github.com/django/django/pull/18356#pullrequestreview-2166340541
New description:
Expressions which evaluate to `NULL` within
`UniqueConstraint(*expressions, nulls_distinct=False)` are still treated
as distinct by `UniqueConstraint.validate()`. This means a
`ValidationError` is not raised when it should be.
Similarly, if the database connection uses
`interprets_empty_strings_as_nulls` this is also ignored by `.validate()`.
Should #35575 be merged, this problem would also extend to any
`GeneratedField` included in `UniqueConstraint(fields=[...],
nulls_distinct=False)`.
E.g.
{{{
class Book(models.Model):
name = CharField(max_length=255, null=True, blank=True)
class Meta:
constraints = [
UniqueConstraint(F("name"), nulls_distinct=False,
name="book_name_null_unique")
]
}}}
then
{{{
> Book.objects.create(name=None)
> book = Book(name=None)
> book.full_clean() # Should raise a `ValidationError` but doesn't.
> book.save() # The database raises a `UniqueViolation`.
}}}
This ticket was raised following discussion in
https://github.com/django/django/pull/18356#pullrequestreview-2166340541
--
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Ticket URL: <https://code.djangoproject.com/ticket/35594#comment:1>
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