Fixed #3463 -- EmptyQuerySet's iterator() now returns a generator. Thanks, Gary Wilson

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4475 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/query.py

@@ -167,17 +167,16 @@ class QuerySet(object):
 
     def iterator(self):
         "Performs the SELECT database lookup of this QuerySet."
-        # self._select is a dictionary, and dictionaries' key order is
-        # undefined, so we convert it to a list of tuples.
-        extra_select = self._select.items()
-
-        cursor = connection.cursor()
-        
         try:
             select, sql, params = self._get_sql_clause()
         except EmptyResultSet:
             raise StopIteration
 
+        # self._select is a dictionary, and dictionaries' key order is
+        # undefined, so we convert it to a list of tuples.
+        extra_select = self._select.items()
+
+        cursor = connection.cursor()
         cursor.execute("SELECT " + (self._distinct and "DISTINCT " or "") + ",".join(select) + sql, params)
         fill_cache = self._select_related
         index_end = len(self.model._meta.fields)
@@ -523,11 +522,18 @@ class QuerySet(object):
         return select, " ".join(sql), params
 
 class ValuesQuerySet(QuerySet):
-    def iterator(self):
+    def __init__(self, *args, **kwargs):
+        super(ValuesQuerySet, self).__init__(*args, **kwargs)
         # select_related and select aren't supported in values().
         self._select_related = False
         self._select = {}
 
+    def iterator(self):
+        try:
+            select, sql, params = self._get_sql_clause()
+        except EmptyResultSet:
+            raise StopIteration
+
         # self._fields is a list of field names to fetch.
         if self._fields:
             columns = [self.model._meta.get_field(f, many_to_many=False).column for f in self._fields]
@@ -536,14 +542,8 @@ class ValuesQuerySet(QuerySet):
             columns = [f.column for f in self.model._meta.fields]
             field_names = [f.attname for f in self.model._meta.fields]
         
-        cursor = connection.cursor()
-        
-        try:
-            select, sql, params = self._get_sql_clause()
-        except EmptyResultSet:
-            raise StopIteration
-        
         select = ['%s.%s' % (backend.quote_name(self.model._meta.db_table), backend.quote_name(c)) for c in columns]
+        cursor = connection.cursor()
         cursor.execute("SELECT " + (self._distinct and "DISTINCT " or "") + ",".join(select) + sql, params)
         while 1:
             rows = cursor.fetchmany(GET_ITERATOR_CHUNK_SIZE)
@@ -592,9 +592,6 @@ class EmptyQuerySet(QuerySet):
         super(EmptyQuerySet, self).__init__(model)
         self._result_cache = []
         
-    def iterator(self):
-        raise StopIteration
-        
     def count(self):
         return 0
         
@@ -606,6 +603,9 @@ class EmptyQuerySet(QuerySet):
         c._result_cache = []
         return c
 
+    def _get_sql_clause(self):
+        raise EmptyResultSet
+
 class QOperator(object):
     "Base class for QAnd and QOr"
     def __init__(self, *args):

tests/modeltests/lookup/models.py

@@ -198,6 +198,8 @@ DoesNotExist: Article matching query does not exist.
 []
 >>> Article.objects.none().count()
 0
+>>> [article for article in Article.objects.none().iterator()]
+[]
 
 # using __in with an empty list should return an empty query set
 >>> Article.objects.filter(id__in=[])