ArrayField and JSONField form fields fail on already converted values

[Brandon Chinn]

If I make a model Foo with the PostgreSQL ArrayField,

class Foo(models.Model):
    bar = ArrayField(models.CharField(...))

And create a ModelForm:

FooForm = modelform_factory(Foo, excludes=[])

The field will fail with already-converted values, like

foo = Foo.objects.create(bar=['a', 'b'])
data = model_to_dict(foo) # {'bar': ['a', 'b']}
form = FooForm(instance=foo, data=data)
form.full_clean() # errors at django/contrib/postgres/forms/array.py:39

Shouldn't already converted values be checked in the to_python method of ArrayField? (Same with JSONField)

[Brandon Chinn]

Fixed in pull request: ​https://github.com/django/django/pull/7012

[Claude Paroz]

I think the solution you proposed in your patch is good for ArrayField, but it might be more tricky for JSONField as a string can be both a converted and an unconverted value, so the isinstance is not covering all cases (see #25532).

[Brandon Chinn]

For JSONField, what about making a custom six.text_type for converted strings, like #25532:

class JsonStr(six.text_type):
    pass

def to_python(self, value):
    ...
    if isinstance(value, JsonStr):
        return value
    val = json.loads(value)
    if isinstance(val, str):
        return JsonStr(val)
    else:
        return val

[Josh Harwood]

Work is all done, just needs a minor change to the name of the type used, however I can't edit this PR, only the merged code so I've removed myself from this ticket.

[Simon Charette]

Please don't mark your own patch as RFC. See our contributing guidelines for more details.

​PR.

[Emad Mokhtar]

I ran the tests with changes nothing failed and ran the same tests without changes and it failed.

Note: I ran tests using PostgreSQL 9.3

[Tim Graham <timograham@…>]

In 6573274:

Refs #27003 -- Fixed SimpleArrayField crash on converted values.

[Tim Graham <timograham@…>]

In eed61500:

Refs #27003 -- Fixed JSONField crash on converted values.