#35848: Problem with UniqueConstraint on fields, one of which allows NULL value.
-------------------------------------+-------------------------------------
Reporter: platonovap | Type: Bug
Status: new | Component:
| Uncategorized
Version: 5.1 | Severity: Normal
Keywords: UniqueConstraint, | Triage Stage:
nullable, null | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
UniqueConstraint does not work correctly for several fields, one of which
is nullable.
{{{
class MyModel(models.Model):
id = models.BigAutoField(primary_key=True, editable=False)
name = models.CharField(max_length=1000, verbose_name="Name")
measure = models.ForeignKey(
Measure,
related_name="mymodel_measure",
on_delete=models.SET_NULL,
null=True,
blank=True,
verbose_name="Measure",
)
class Meta:
constraints = [
models.UniqueConstraint(
fields=["name"],
name="mymodel_unique_name_measure_null",
condition=Q(measure__isnull=True),
violation_error_message="Error message for null",
),
models.UniqueConstraint(
fields=["name", "measure"],
name="mymodel_unique_name_measure_not_null",
condition=Q(measure__isnull=False),
violation_error_message="Error message for not null",
),
]
}}}
Database - Postgres 15.
The error is as follows: if there is a record with the field measure = not
null, you can create a new record with the same name and measure = null.
And if there is an entry with measure = null, then a new entry with the
same name and measure = not null does not work.
From the Postgres side, Constraints are created and working correctly.
Error message:
{{{
{
"error": "{'name': [ErrorDetail(string='The name of the mymodel with
this Name already exists.', code='unique')]}"
}
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/35848>
Django <https://code.djangoproject.com/>
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