Ticket #7298: prevent_update_queryset_r7599.patch

django/db/models/query.py

@@ -292 +292 @@
         Updates all elements in the current QuerySet, setting all the given
         fields to the appropriate values.
         """
+        assert self.query.can_filter(), \
+                "Cannot update a query once a slice has been taken."
         query = self.query.clone(sql.UpdateQuery)
         query.add_update_values(kwargs)
         query.execute_sql(None)
@@ -306 +308 @@
         code (it requires too much poking around at model internals to be
         useful at that level).
         """
+        assert self.query.can_filter(), \
+                "Cannot update a query once a slice has been taken."
         query = self.query.clone(sql.UpdateQuery)
         query.add_update_fields(values)
         query.execute_sql(None)

tests/modeltests/update/models.py

@@ -63 +63 @@
 >>> DataPoint.objects.values('value').distinct()
 [{'value': u'thing'}]
 
+We do not support update on already sliced query sets.
+
+>>> DataPoint.objects.all()[:2].update(another_value='another thing') 
+Traceback (most recent call last):
+    ...
+AssertionError: Cannot update a query once a slice has been taken.
+
 """
 }