Fixed #10766 -- Raise an error when annotate() references another agg…

…reagte(). Thanks to aseering@mit.edu for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10521 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/sql/query.py

@@ -1403,6 +1403,9 @@ def add_aggregate(self, aggregate, model, alias, is_summary):
             field_name = field_list[0]
             col = field_name
             source = self.aggregates[field_name]
+            if not is_summary:
+                raise FieldError("Cannot compute %s('%s'): '%s' is an aggregate" % (
+                    aggregate.name, field_name, field_name))
         elif ((len(field_list) > 1) or
             (field_list[0] not in [i.name for i in opts.fields]) or
             self.group_by is None or

tests/regressiontests/aggregation_regress/models.py

@@ -297,6 +297,11 @@ def __unicode__(self):
 >>> HardbackBook.objects.annotate(n_authors=Count('authors')).values('name','n_authors')
 [{'n_authors': 2, 'name': u'Artificial Intelligence: A Modern Approach'}, {'n_authors': 1, 'name': u'Paradigms of Artificial Intelligence Programming: Case Studies in Common Lisp'}]
 
+# Regression for #10766 - Shouldn't be able to reference an aggregate fields in an an aggregate() call.
+>>> Book.objects.all().annotate(mean_age=Avg('authors__age')).annotate(Avg('mean_age'))
+Traceback (most recent call last):
+...
+FieldError: Cannot compute Avg('mean_age'): 'mean_age' is an aggregate
 
 """
 }