Support nested serializers in SimpleMetadata's representation of metadata

[Ernest0x]

With this commit, nested serializer fields in the representation done by SimpleMetadata class are getting a type of 'serializer' and a 'fields' attribute containing metadata for their inner fields.

[xordoquy]

I don't really get what this change is about. Mind explaining a bit more why this is required and possible add a test case to illustrate it ?

[Ernest0x]

@xordoquy of course, here is an example:

Consider the following serializers:

class NestedSerializer(serializers.Serializer):
    some_text = serializers.CharField(max_length=100)
    another_text = serializers.CharField(max_length=100)

class RootSerializer(serializers.Serializer):
    nest = NestedSerializer()
    some_note = serializers.CharField(max_length=100)
    another_note = serializers.CharField(max_length=100)

Now you write a view like this:

class RootList(generics.ListCreateAPIView):
    queryset = Root.objects.all()
    serializer_class = RootSerializer
    metadata_class = SimpleMetadata

With this commit, the representation of metadata in an OPTIONS request will look like this:

{
    "name": "Root List",
    "description": "List existing 'Root' items, or create a new item.",
    "renders": [
        "application/json",
        "text/html"
    ],
    "parses": [
        "application/json",
        "application/x-www-form-urlencoded",
        "multipart/form-data"
    ],
    "actions": {
        "POST": {
            "nest": {
                "type": "serializer",
                "required": true,
                "read_only": false,
                "label": "nest",
                "fields": {
                     "some_text": {
                         "type": "string",
                         "required": true,
                         "read_only": false,
                         "label": "some text",
                         "max_length": 100
                     },
                     "another_text": {
                         "type": "string",
                         "required": true,
                         "read_only": false,
                         "label": "another text",
                         "max_length": 100
                     }
                }
            },
            "some_note": {
                "type": "string",
                "required": true,
                "read_only": false,
                "label": "some note",
                "max_length": 100
            },
            "another_note": {
                "type": "string",
                "required": true,
                "read_only": false,
                "label": "another note",
                "max_length": 100
            }
        }
    }
}

As you can see, the "nest" field has a "fields" attribute that expands the inner fields of the nested serializer.

[tomchristie]

The motivation here is reasonable enough, but let's not start with a pull request until we've discussed through in an issue...

• What the current style looks like.
• What alternative styles we might use instead.

Happy to accept this as an issue, but I expect the answer to the second of those points might be slightly different to what you're presenting in this pull request, so best to start with a conversation, rather than a code change. 😄