ArrayField should implement from_db_value()

[Odahi]

I'm using a custom field with the new Postgres ArrayField:

class Tag(object):
   def __init__(self, id):
        self.id = id

   def __unicode__(self):
        return U"Tag(%d)" % self.id


class TagField(models.SmallIntegerField):
    # Dummy wrapper over SmallIntegerField.

   def from_db_value(self, value, expression, connection, context):
        if value is None:
            return value
        return Tag(int(value))

   def get_prep_value(self, value):
        return value
   ...

# models.py

class Recommendation(models.Model):
    tags = ArrayField(TagField(), size=3)

    def __unicode__(self):
        return self.tags

Then

>>> Recommendation.objects.create(tags=[Tag(1), Tag(2)])
>>> Recommendation.objects.all()

[<Recommendation: [1, 2]>]  # WRONG

This is wrong because I got Integers instead of Tag objects:

[<Recommendation: [Tag(1), Tag(2)]>]  # OK

Looking at the ArrayField source code seems that to_python() is implemented but never called. I think from_db_value() should be also implemented.

[Tim Graham]

Can you propose a patch and regression test?

[Odahi]

Replying to timgraham:

Can you propose a patch and regression test?

Hello Tim, never did it before, but I think I can submit a tentative patch & test for this in the next days. I'll try.

[Odahi]

I've just added a tentative patch:

​https://github.com/Odahi/django/tree/ticket_25143
​https://github.com/django/django/pull/5035

Would be great if someone can check it.

[Tim Graham]

See #25579 for a related issue (querying on complex types) that could be fixed along with this.

[Tim Graham]

​Updated PR

[Tim Graham <timograham@…>]

In 2495023:

Fixed #25143 -- Added ArrayField.from_db_value().

Thanks Karan Lyons for contributing to the patch.