Validation of check constraints against ranges involving PostgreSQL's lower()/upper() functions produces invalid SQL.

[David Sanders]

Given a model using the Postgres field IntegerRangeField:

class Sample(models.Model):
    value_range = IntegerRangeField(null=True, blank=True)

    class Meta:
        constraints = [
            CheckConstraint(
                name="positive_value_range",
                check=Q(value_range__startswith__gte=0),
            ),
        ]

validation of the check constraint produces a DatabaseError:

sample = Sample()
sample.validate_constraints()

Got a database error calling check() on <Q: (AND: (AND: ('value_range__startswith__gte', 0)))>: operator does not exist: text >= integer
LINE 1: SELECT 1 AS "_check" WHERE lower(NULL) >= 0
                                               ^
HINT:  No operator matches the given name and argument types. You might need to add explicit type casts.

This is because Postgres' lower() and upper() functions are overloaded to accept either text or range types - the former for converting case with the latter retrieving the lower/upper bounds of the range.

When an expression LOWER(NULL) is encountered without an underlying column Postgres assumes the resulting expression is text:

postgres=# select UPPER(NULL);
 upper
-------
 NULL!
(1 row)

postgres=# \gdesc
 Column | Type
--------+------
 upper  | text
(1 row)

I doubt this is a serious error though because upon inspecting the new constraint validation code any DatabaseError is caught and a warning is logged but it would be nice to have a functioning check for this.

I have written a test & small patch which pretty much just adapts some existing operand casting code for Postgres (I haven't signed the CLA yet though because I'm not sure if someone else might want to dry it up a bit with a common mixin?)

[David Sanders]

PR: ​https://github.com/django/django/pull/15931

[Mariusz Felisiak]

Thanks for the report! Bug in 667105877e6723c6985399803a364848891513cc.

[Mariusz Felisiak <felisiak.mariusz@…>]

In e0ac72fe:

Refs #33905 -- Added test for CheckConstraint() validation with ArrayField and contains.

[Mariusz Felisiak <felisiak.mariusz@…>]

In e0ae1363:

Fixed #33905 -- Fixed CheckConstraint() validation on range fields.

Bug in 667105877e6723c6985399803a364848891513cc.

[Mariusz Felisiak <felisiak.mariusz@…>]

In e215948f:

[4.1.x] Fixed #33905 -- Fixed CheckConstraint() validation on range fields.

Bug in 667105877e6723c6985399803a364848891513cc.

Backport of e0ae1363ec2aa71945be26f869cafd4181ccbc95 from main