Allow passing models.Manager to RelatedField.queryset

rest_framework/relations.py

@@ -5,6 +5,7 @@ from django.core.exceptions import ImproperlyConfigured, ObjectDoesNotExist
 from django.core.urlresolvers import (
     NoReverseMatch, Resolver404, get_script_prefix, resolve
 )
+from django.db import models
 from django.db.models.query import QuerySet
 from django.utils import six
 from django.utils.encoding import smart_text
@@ -87,7 +88,7 @@ class RelatedField(Field):
 
     def get_queryset(self):
         queryset = self.queryset
-        if isinstance(queryset, QuerySet):
+        if isinstance(queryset, (QuerySet, models.Manager)):
             # Ensure queryset is re-evaluated whenever used.
             queryset = queryset.all()
         return queryset