Request: minLength if allow_blank=False

[HansAarneLiblik]

Currently drf-yasg (from which were migrating) adds minLength: 1 to schema if field is not required and has default value, ie

depth = serializers.CharField(required=False, default='2')

and this generates schema

- name: depth
  in: query
  required: false
  type: string
  default: '2'
  minLength: 1

which means user CAN NOT make request api.foo.com?depth=''

drf-spectacular does not add minLength value for this

- in: query
  name: depth
  schema:
    type: string
    default: '2'

This minLength: 1 value should come from allow_blank attr that for CharField default to False

[johnthagen]

This is something I noticed as well when I migrated from drf-yasg but I didn't think through the ramifications until reading this post.

[johnthagen]

This also seems related to or duplicate of #186

[tfranzel]

it turns out that #186 is slightly different. Serializer fields have no allow_blank concept and ModelSerializers generated from models apparently lose this information.

Here however, we may be able to cut some corners (default) and detect his case when a serializer is exploded as part of parameter extraction.

EDIT: my statement is likely not correct. I have to take a deeper look.

[tfranzel]

had another detailed look. i was briefly misled by the default. imho it plays no relevant part here. '' is a valid string and the default only comes into play when the field is actually missing.

extended OpenApiParameter to also expose this. I assume you used the exploded serializer for the parameters. this shortcut now makes use of allow_blank==False and so your example should now work as expected.

[tfranzel]

closing this issue for now. feel free to comment if anything is missing or not working and we will follow-up.

[johnthagen]

@tfranzel I noticed that these checks were in the 0.21.0 schema as well.