Ticket #11256: aggregate-validation.diff

django/db/models/query.py

@@ -605 +605 @@
         Return a query set in which the returned objects have been annotated
         with data aggregated from related fields.
         """
+        total_aggregates = len(args) + len(kwargs)
         for arg in args:
             kwargs[arg.default_alias] = arg
 
+        if len(kwargs) != total_aggregates:
+            raise ValueError("Some of the aggregates had duplicate aliases, "
+                "check to make sure none of your aggregates conflict with the "
+                "default aliases.")
+
+        names = set([f.name for f in self.model._meta.fields])
+        for aggregate in kwargs:
+            if aggregate in names:
+                raise ValueError("The %s aggregate conflicts with a field on "
+                    "the model." % aggregate)
+
+
         obj = self._clone()
 
         obj._setup_aggregate_query(kwargs.keys())

tests/regressiontests/aggregation_regress/models.py

@@ -318 +318 @@
 ...
 FieldError: Cannot compute Avg('mean_age'): 'mean_age' is an aggregate
 
+>>> Book.objects.all().annotate(Avg('authors__age'), authors__age__avg=Avg('authors__age'))
+Traceback (most recent call last):
+...
+ValueError: Some of the aggregates had duplicate aliases, check to make sure none of your aggregates conflict with the default aliases.
+
+>>> Author.objects.annotate(age=Avg('friends__age'))
+Traceback (most recent call last):
+...
+ValueError: The age aggregate conflicts with a field on the model.
+
 """
 }