Refs #28459 -- Improved performance of FlatValuesListIterable.

django/db/models/query.py

@@ -8,6 +8,7 @@ import sys
 import warnings
 from collections import OrderedDict, deque
 from contextlib import suppress
+from itertools import chain
 
 from django.conf import settings
 from django.core import exceptions
@@ -145,8 +146,7 @@ class FlatValuesListIterable(BaseIterable):
     def __iter__(self):
         queryset = self.queryset
         compiler = queryset.query.get_compiler(queryset.db)
-        for row in compiler.results_iter():
-            yield row[0]
+        return chain.from_iterable(compiler.results_iter())
 
 
 class QuerySet:
@@ -302,6 +302,9 @@ class QuerySet:
     # METHODS THAT DO DATABASE QUERIES #
     ####################################
 
+    def _iterator(self, use_chunked_fetch, chunk_size):
+        yield from self._iterable_class(self, chunked_fetch=use_chunked_fetch, chunk_size=chunk_size)
+
     def iterator(self, chunk_size=2000):
         """
         An iterator over the results from applying this QuerySet to the
@@ -310,7 +313,7 @@ class QuerySet:
         if chunk_size <= 0:
             raise ValueError('Chunk size must be strictly positive.')
         use_chunked_fetch = not connections[self.db].settings_dict.get('DISABLE_SERVER_SIDE_CURSORS')
-        return iter(self._iterable_class(self, chunked_fetch=use_chunked_fetch, chunk_size=chunk_size))
+        return self._iterator(use_chunked_fetch, chunk_size)
 
     def aggregate(self, *args, **kwargs):
         """