Add LazyExtraFieldsHyperlinkedModelSerializer

This class is a mixin of LazyExtraFieldsSerializerMixin and
serializers.HyperlinkedModelSerializer. It allows adding fields
to a 3rd party app serializer without having to import the serializer.
Referencing is done using the dotted path of the serializer.

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/apps/rest_api/serializers.py

@@ -0,0 +1,38 @@
+from __future__ import absolute_import, unicode_literals
+
+from django.core.exceptions import ImproperlyConfigured
+from django.utils.translation import ugettext_lazy as _
+
+from rest_framework import serializers
+from rest_framework.generics import get_object_or_404
+from rest_framework.reverse import reverse
+
+
+class LazyExtraFieldsSerializerMixin(object):
+    _registry = {}
+
+    @classmethod
+    def add_field(cls, dotted_path, field_name, field):
+        cls._registry.setdefault(dotted_path, {})
+        cls._registry[dotted_path][field_name] = field
+
+    @classmethod
+    def get_fields_for(cls, dotted_path):
+        return cls._registry.get(dotted_path, {}).items()
+
+    def get_dotted_path(self):
+        return '{}.{}'.format(self.__module__, self.__class__.__name__)
+
+    def get_extra_fields(self):
+        return self.__class__.get_fields_for(dotted_path=self.get_dotted_path())
+
+    def __init__(self, *args, **kwargs):
+        for field_name, field in self.get_extra_fields():
+            self._declared_fields[field_name] = field
+            self.__class__.Meta.fields += (field_name,)
+
+        super(LazyExtraFieldsSerializerMixin, self).__init__(*args, **kwargs)
+
+
+class LazyExtraFieldsHyperlinkedModelSerializer(LazyExtraFieldsSerializerMixin, serializers.HyperlinkedModelSerializer):
+    pass