Incorrect value when annotating empty list as Value() on ArrayField.

[Matthew Schinckel]

I have a nice simple minimal case that shows this.

You can try this on any model: auth.User was just convenient for example. You'll need at least one object in there to query.

from django.contrib.auth.models import User
from django.contrib.postgres.fields import ArrayField
from django.db.models.expressions import Value
from django.db.models import IntegerField

User.objects.annotate(foo=Value([1], output_field=ArrayField(IntegerField()))).first().foo
# Outputs [1], as expected

User.objects.annotate(foo=Value([], output_field=ArrayField(IntegerField()))).first().foo
# Outputs '{}', which is _not_ correct.

[Matthew Schinckel]

Still a problem in current development head.

[Tim Graham]

#28762 may be related if not a duplicate.

[Tomer Chachamu]

I added an (expected failing) test in #28762 for this.

I think this ticket will be easier to fix after #28762 . The problem is that psycopg2 adapts the empty list to '{}'. We cannot simply send ARRAY[] because this causes ERROR: cannot determine type of empty array. However we can send '{}'::integer[].

ArrayField.db_type() is already implemented and returns 'integer[]' so we can pass that value to ArrayLiteral and always output it into the SQL.

This might break something else, we'll see.

[GitHub <noreply@…>]

In 654614b3:

Refs #28767 -- Added test for annotating Value() with empty list as an ArrayField.

Fixed in 3af695eda24b874486ee8be7e0d729761b3bdc71.

[Mariusz Felisiak]

Fixed in 3af695eda24b874486ee8be7e0d729761b3bdc71.