Fix schema generation for PrimaryKeyRelatedField

[jlaine]

By default all subclasses of RelatedField are output as string fields in
the schema, which works well for StringRelatedField, SlugRelatedField or
HyperlinkedRelatedField.

Handle the common case of a PrimaryKeyRelatedField pointing to an
AutoField.

[jlaine]

On a related note, I noticed that including a foreign key field in "read_only_fields" nukes the "queryset" kwarg:

django-rest-framework/rest_framework/serializers.py

Line 1291 in 2709de1

'validators', 'queryset'

I understand why having this attribute is not required for a read-only field, but what is the harm in keeping it? Nuking this attribute removes the link to the foreign model and makes it much harder to generate a schema for the output of a serializer.

[carltongibson]

@jlaine Just on your related note: my immediate thought is that if read_only_fields is misbehaving for you is to explicitly declare the field. read_only_fields is a short-cut, it's task is to cover the common-case. The canonical approach is always to explicitly declare the field.

If that doesn't suit then put together a proper description and open a new ticket and we'll have a look.

[carltongibson]

Yep. This looks good. Thanks!

[jlaine]

Thanks for merging this! Concerning the read_only_fields, explicitly declaring the field doesn't help : there is code to prevent you from providing a queryset on a field you declare as read_only. Not sure what the rationale is:

django-rest-framework/rest_framework/relations.py

Line 103 in ffe3dbb

assert not (self.queryset is not None and kwargs.get('read_only', None)), (

[carltongibson]

OK. Open a new ticket and we’ll think it through