Model CharFiled with choices attribute mapped to regular Serializer CharField instead of ChoicesField when editable is set to False

[MohamedAbdultawab]

As I understand, model CharField with choices attribute should be mapped to Serializer ChoicesField, which happens in most cases, but the problem is when model CharField has editable=False, the line at rest_framework/utils/field_mapping.py:98 checks if the field has editable set to False then ignores all other checks, and one of the ignored check is the check that adds the choices attribute to serializer kwargs, which will later be used to determine the serializer field to be used.

[yyyyyyyan]

Hi! This is by design. A ChoiceField is a field that can accept a value out of a limited set of choices [1]. If your field is not editable, Django assumes it's not supposed to be set [2], so the field won't show up in the admin or any ModelForm. With DRF and serializers it's the same! Since it's not supposed to be set to any value, it doesn't make sense to use a ChoiceField, because there's no need for validation.

[vakorol]

The problem with the current implementation is that the corresponding schema (for example, OpenAPI) for the model field does not describe the possible values correctly. This makes the schema a bit less useful when it comes to describing fields returned via GET requests, for example.

So, although @yyyyyyyan's argument above is valid, it is missing the issue with the schema:

Since it's not supposed to be set to any value, it doesn't make sense to use a ChoiceField, because there's no need for validation.

[yyyyyyyan]

OpenAPI schemas can be manually created or modified. If you are using a schema generation tool like drf-spectacular or drf-yasg, you can always modify the behaviour of the automated generation. With drf-spectacular you can use the enum argument of drf_spectacular.utils.OpenApiParameter:

OpenApiParameter(
    "ordering",
    description="Which field to use when ordering the results. Use `-{field}` for descending order.",
    enum=["id", "title", "cost", "-id", "-title", "-cost"],
    default="id",
)

Which will generate something like this in the schema:

parameters:
- in: query
  name: ordering
  schema:
    type: string
    enum:
    - -cost
    - -id
    - -title
    - cost
    - id
    - title
    default: id
  description: Which field to use when ordering the results. Use `-{field}` for descending order.

[vakorol]

Yes, of course. I am using an extended DRF's AutoSchema, though. And my problem is that tools provided by DRF iself create a schema that is incomplete..