Dynamic object-dependent metadata

[leifurhauks]

It would be useful to be able to specify that a field or fields on a serializer should appear in the meta object rather than in data['attributes']. Perhaps a field could be marked (with a kwarg or attribute on the serializer) as metadata so that the renderer knows to put it in the meta section?

[jerel]

Good question, I'm likely going to need this feature myself next week. Currently the meta is set by pagination and I implemented it in sort of a stop gap manner.

So there is fields, read_only_fields, and write_only_fields now. I could imagine a meta_fields property fitting in nicely. However we should think about customization: is meta_fields plus SerializerMethodField the best way to add arbitrarily deep meta structures? Should the renderer call a hook on each serializer to allow it to add/modify meta info?

[jsenecal]

Actually, IMO, Using the serializer's fields in meta makes sense as the behavior of getting instance related data is what the serializer itself is made for...

A usage I have myself is a custom PermissionField that inherits from the base Field class.

I don't think it should be too hard to write an extract_meta method and use the fields declared as an attribute like we did for included_serializers in that method. The extract_attributes would then avoid going through those.

[riklaunim]

What about adding meta to object list endpoints? The pull request handles detail requests with get_root_meta but not lists.

[jerel]

@riklaunim they were supposed to work the same. Looks like this test needs to be duplicated and modified to fetch a list instead of a single post so we can test that case. https://github.com/django-json-api/django-rest-framework-json-api/blob/develop/example/tests/integration/test_meta.py#L10

[riklaunim]

I've added the test for list view.

Also the most handy metadata for typical list/get/create/update frontend apps is under OPTIONS request in DRF - like options for choices fields or max lengths, is required etc. That meta can be fetched in code http://www.django-rest-framework.org/api-guide/metadata/#creating-schema-endpoints :

meta = self.metadata_class()
data = meta.determine_metadata(request, self)

But it expects to be called in a view not in the serializer. So either second request (OPTIONS) is required or some way to add the most interesting part of that metadata to default metadata of normal requests.