Merge pull request #27 from adesor/get-queryset-mixin

Eliminate the need for overriding get_queryset() for filtering logic

Author: manjitkumar

README.md

@@ -79,6 +79,9 @@ class PlayersViewSet(FiltersMixin, viewsets.ModelViewSet):
     This viewset automatically provides `list`, `create`, `retrieve`,
     `update` and `destroy` actions.
     """
+    queryset = Player.objects.prefetch_related(
+        'teams'  # use prefetch_related to minimize db hits.
+    ).all()
     serializer_class = PlayerSerializer
     pagination_class = ResultSetPagination
     filter_backends = (filters.OrderingFilter,)
@@ -103,30 +106,6 @@ class PlayersViewSet(FiltersMixin, viewsets.ModelViewSet):
 
     # add validation on filters
     filter_validation_schema = players_query_schema
-
-    def get_queryset(self):
-        """
-        Optionally restricts the queryset by filtering against
-        query parameters in the URL.
-        """
-        query_params = self.request.query_params
-        url_params = self.kwargs
-
-        # get queryset_filters from FilterMixin
-        queryset_filters = self.get_db_filters(url_params, query_params)
-
-        # This dict will hold filter kwargs to pass in to Django ORM calls.
-        db_filters = queryset_filters['db_filters']
-
-        # This dict will hold exclude kwargs to pass in to Django ORM calls.
-        db_excludes = queryset_filters['db_excludes']
-
-        # fetch queryset from Players model
-        queryset = Player.objects.prefetch_related(
-            'teams'  # use prefetch_related to minimize db hits.
-        ).all()
-
-        return queryset.filter(**db_filters).exclude(**db_excludes)
 ```
 
 With the use of `drf-url-filters` adding a new filter on a new column is as

filters/decorators.py

@@ -0,0 +1,18 @@
+
+def decorate_get_queryset(f):
+    def decorated(self):
+        queryset = f(self)
+        query_params = self.request.query_params
+        url_params = self.kwargs
+
+        # get queryset_filters from FiltersMixin
+        queryset_filters = self.get_db_filters(url_params, query_params)
+
+        # This dict will hold filter kwargs to pass in to Django ORM calls.
+        db_filters = queryset_filters['db_filters']
+
+        # This dict will hold exclude kwargs to pass in to Django ORM calls.
+        db_excludes = queryset_filters['db_excludes']
+
+        return queryset.filter(**db_filters).exclude(**db_excludes)
+    return decorated

filters/metaclasses.py

@@ -0,0 +1,13 @@
+from .decorators import decorate_get_queryset
+
+
+class MetaFiltersMixin(type):
+    def __new__(cls, name, bases, dct):
+        if 'get_queryset' in dct:
+            dct['get_queryset'] = decorate_get_queryset(dct['get_queryset'])
+        return super(MetaFiltersMixin, cls).__new__(cls, name, bases, dct)
+
+    def __setattr__(self, attr, val):
+        if attr == 'get_queryset':
+            val = decorate_get_queryset(val)
+        return super(MetaFiltersMixin, self).__setattr__(attr, val)

filters/mixins.py

@@ -2,6 +2,7 @@
 from voluptuous import Invalid
 from rest_framework.exceptions import ParseError
 
+from .metaclasses import MetaFiltersMixin
 from .schema import base_query_params_schema
 
 
@@ -11,6 +12,7 @@ class FiltersMixin(object):
     filters by applying defined filters on generic
     queryset.
     '''
+    __metaclass__ = MetaFiltersMixin
 
     def __get_queryset_filters(self, query_params, *args, **kwargs):
         '''
@@ -87,3 +89,11 @@ def get_db_filters(self, url_params, query_params):
             'db_filters': db_filters,
             'db_excludes': db_excludes,
         }
+
+    def get_queryset(self):
+        # Defined here to handle the case where the viewset
+        # does not override get_queryset
+        # (and hence the metaclass would not have been
+        # able to decorate it with the filtering logic.)
+
+        return super(FiltersMixin, self).get_queryset()