Fixed #27639 -- Added chunk_size parameter to QuerySet.iterator().

tests/queries/test_iterator.py

@@ -0,0 +1,39 @@
+import datetime
+from unittest import mock
+
+from django.db.models.sql.compiler import cursor_iter
+from django.test import TestCase
+
+from .models import Article
+
+
+class QuerySetIteratorTests(TestCase):
+    itersize_index_in_mock_args = 3
+
+    @classmethod
+    def setUpTestData(cls):
+        Article.objects.create(name='Article 1', created=datetime.datetime.now())
+        Article.objects.create(name='Article 2', created=datetime.datetime.now())
+
+    def test_iterator_invalid_chunk_size(self):
+        for size in (0, -1):
+            with self.subTest(size=size):
+                with self.assertRaisesMessage(ValueError, 'Chunk size must be strictly positive.'):
+                    Article.objects.iterator(chunk_size=size)
+
+    def test_default_iterator_chunk_size(self):
+        qs = Article.objects.iterator()
+        with mock.patch('django.db.models.sql.compiler.cursor_iter', side_effect=cursor_iter) as cursor_iter_mock:
+            next(qs)
+        self.assertEqual(cursor_iter_mock.call_count, 1)
+        mock_args, _mock_kwargs = cursor_iter_mock.call_args
+        self.assertEqual(mock_args[self.itersize_index_in_mock_args], 2000)
+
+    def test_iterator_chunk_size(self):
+        batch_size = 3
+        qs = Article.objects.iterator(chunk_size=batch_size)
+        with mock.patch('django.db.models.sql.compiler.cursor_iter', side_effect=cursor_iter) as cursor_iter_mock:
+            next(qs)
+        self.assertEqual(cursor_iter_mock.call_count, 1)
+        mock_args, _mock_kwargs = cursor_iter_mock.call_args
+        self.assertEqual(mock_args[self.itersize_index_in_mock_args], batch_size)