#34149: Postgres "ExclusionConstraint with conditions cannot be deferred." seems
wrong
--------------------------------------------+------------------------
Reporter: Márton Salomváry | Owner: (none)
Type: Bug | Status: new
Component: contrib.postgres | Version: 4.1
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 |
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When attempting to add a constraint to a model that looks something like
this:
{{{
ExclusionConstraint(
name="my_constraint",
expressions=[
("is_default", RangeOperators.EQUAL),
],
condition=Q(is_default=False),
deferrable=Deferrable.DEFERRED,
)
}}}
`makemigrations` fails with the following error:
{{{
ExclusionConstraint(
File "django/contrib/postgres/constraints.py", line 55, in __init__
raise ValueError("ExclusionConstraint with conditions cannot be
deferred.")
ValueError: ExclusionConstraint with conditions cannot be deferred.
}}}
However PostgreSQL 14.5 seems to be perfectly fine with the following:
{{{
ALTER TABLE my_model
ADD CONSTRAINT my_constraint
EXCLUDE (is_default WITH =)
WHERE (is_default = TRUE)
INITIALLY DEFERRED;
}}}
I've tried to figure out why this restriction may be in place but neither
other parts of Django nor PostgreSQL itself seem to require deferred
exclusion constraints to not have a condition.
The commit that added this also does not seem to explain the situation:
https://github.com/django/django/commit/b4068bc65636cca6c2905aa8c40bea69bb0e4245
Maybe an accidental copypaste from here?
https://github.com/django/django/blob/35911078fa40eb35859832987fedada76963c01e/django/db/models/constraints.py#L153-L154
--
Ticket URL: <https://code.djangoproject.com/ticket/34149>
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