JSONField(default=dict) and using .get() results in an (unexpected) error.

[NiekvanderLinden]

Bug report

What's wrong

Seems that using JSONField(default=dict) and using .get() results in an (unexpected) error.

error: Item "None" of "Optional[Any]" has no attribute "get" [union-attr]

class SomeModel(models.Model):
    data = models.JSONField(default=dict)


some_models = SomeModel.objects.all().values("data")

for i in some_models:
   something = i["data"].get("key")

Results in

error: Item "None" of "Optional[Any]" has no attribute "get" [union-attr]

How is that should be

Since the default in the JSONField is set to dict I would expect django-stubs to recognize the get() method.

System information

• OS:
• python version: 3.8.13
• django version: 3.2.16
• mypy version: 0.961
• django-stubs version: 1.12.0
• django-stubs-ext version: 0.5.0

[orsinium]

A bit more context. We've checked the inferred field type with just a model instance, with only, and with values, and only when using values the type is inferred as Optional[Any] instead of just Any.

a = False
if a:
    reveal_type(SomeModel.objects.get().data)  # Revealed type is "Any"
    reveal_type(SomeModel.objects.values('data').get()['data'])  # Revealed type is "Union[Any, None]"
    reveal_type(SomeModel.objects.only('data').get().data)  # Revealed type is "Any"

[PIG208]

This bugged me too. Also, I expect JSONField should have a more specific type than Any.

[adamchainz]

Unfortunately I don’t think this type can be more specific than Any, for two reasons.

First, because JSONField with a default of dict could still be used to store a list, number, string, or None. Django places no restriction here, the default type is just what will be set if you don’t specify a value.

Second, because using a custom JSON decoder does allow literally any type to be returned.

only when using values the type is inferred as Optional[Any] instead of just Any.

This is odd and could be investigated, I’m not sure why using values would add an Optional. It is probably not JSONField specific...

[orsinium]

Unfortunately I don’t think this type can be more specific than Any, for two reasons.

It would be great to be able to manually refine the type, though:

data: JSONField[dict[str, Any]] = models.JSONField(default=dict)

I tried to do that a few times, no luck. But that's another story and should be a separate issue. This issue is about the type being refined to Optional despite the field being non-nullable.

[sshishov]

Then it should be something like this:

data = models.JSONField[dict[str, Any]](default=dict)

no?

[drutkoowski]

Have you tried:

if TYPE_CHECKING:
    JSONField = models.JSONField[dict[str, Any]]
else:
    JSONField = models.JSONField

and then
json_property = JSONField(...)