add QuerySetWrapper support for reverse m2m __in filtering

src/c3nav/editor/wrappers.py

@@ -370,9 +370,50 @@ class BaseQueryWrapper(BaseWrapper):
 
             filter_type = segments.pop(0)
 
+            if not segments and filter_type == 'in':
+                filter_name = field_name+'__pk__in'
+                filter_value = tuple(obj.pk for obj in filter_value)
+                filter_type = 'pk'
+                segments = ['in']
+                q = Q(**{filter_name: filter_value})
+
             if filter_type == class_value.field.model._meta.pk.name:
                 filter_type = 'pk'
 
+            if filter_type == 'pk' and segments == ['in']:
+                if not class_value.reverse:
+                    raise NotImplementedError
+
+                # so... e.g. we want to get all groups that belong to one of the given spaces.
+                # field_name would be "spaces"
+                model = class_value.field.model  # space
+                filter_value = set(filter_value)  # space pks
+                filter_value_existing = set(pk for pk in filter_value if not self.is_created_pk(pk))
+
+                # get spaces that we are interested about that had groups added or removed
+                m2m_added = {pk: val[field_name] for pk, val in self._changeset.m2m_added.get(model, {}).items()
+                             if pk in filter_value and field_name in val}
+                m2m_removed = {pk: val[field_name] for pk, val in self._changeset.m2m_removed.get(model, {}).items()
+                             if pk in filter_value and field_name in val}  # can only be existing spaces
+
+                # directly lookup groups for spaces that had no groups removed
+                q = Q(**{field_name+'__pk__in': filter_value_existing - set(m2m_removed.keys())})
+
+                # lookup groups for spaces that had groups removed
+                for pk, values in m2m_removed.items():
+                    q |= Q(Q(**{field_name + '__pk': pk}) & ~Q(pk__in=values))
+
+                # get pk of groups that were added to any of the spaces
+                r_added_pks = reduce(operator.or_, m2m_added.values(), set())
+
+                # lookup existing groups that were added to any of the spaces
+                q |= Q(pk__in=tuple(pk for pk in r_added_pks if not self.is_created_pk(pk)))
+
+                # get created groups that were added to any of the spaces
+                created_pks = set(int(pk[1:]) for pk in r_added_pks if self.is_created_pk(pk))
+
+                return q, created_pks
+
             if segments:
                 raise NotImplementedError