Fixed #6785 -- Made QuerySet.get() fetch a limited number of rows.

Co-authored-by: Tim Graham <timograham@gmail.com>
Co-authored-by: Patryk Zawadzki <patrys@room-303.com>
Co-Authored-By: Mariusz Felisiak <felisiak.mariusz@gmail.com>

django/db/models/query.py

@@ -28,6 +28,9 @@ from django.utils import timezone
 from django.utils.functional import cached_property, partition
 from django.utils.version import get_version
 
+# The maximum number of results to fetch in a get() query.
+MAX_GET_RESULTS = 21
+
 # The maximum number of items to display in a QuerySet.__repr__
 REPR_OUTPUT_SIZE = 20
 
@@ -398,6 +401,10 @@ class QuerySet:
         clone = self.filter(*args, **kwargs)
         if self.query.can_filter() and not self.query.distinct_fields:
             clone = clone.order_by()
+        limit = None
+        if not clone.query.select_for_update or connections[clone.db].features.supports_select_for_update_with_limit:
+            limit = MAX_GET_RESULTS
+            clone.query.set_limits(high=limit)
         num = len(clone)
         if num == 1:
             return clone._result_cache[0]
@@ -407,8 +414,10 @@ class QuerySet:
                 self.model._meta.object_name
             )
         raise self.model.MultipleObjectsReturned(
-            "get() returned more than one %s -- it returned %s!" %
-            (self.model._meta.object_name, num)
+            'get() returned more than one %s -- it returned %s!' % (
+                self.model._meta.object_name,
+                num if not limit or num < limit else 'more than %s' % (limit - 1),
+            )
         )
 
     def create(self, **kwargs):

tests/basic/tests.py

@@ -4,7 +4,7 @@ from datetime import datetime, timedelta
 from django.core.exceptions import MultipleObjectsReturned, ObjectDoesNotExist
 from django.db import DEFAULT_DB_ALIAS, DatabaseError, connections, models
 from django.db.models.manager import BaseManager
-from django.db.models.query import EmptyQuerySet, QuerySet
+from django.db.models.query import MAX_GET_RESULTS, EmptyQuerySet, QuerySet
 from django.test import (
     SimpleTestCase, TestCase, TransactionTestCase, skipUnlessDBFeature,
 )
@@ -387,6 +387,26 @@ class ModelTest(TestCase):
         # Fields that weren't deleted aren't reloaded.
         self.assertEqual(article.pub_date, new_pub_date)
 
+    def test_multiple_objects_max_num_fetched(self):
+        max_results = MAX_GET_RESULTS - 1
+        Article.objects.bulk_create(
+            Article(headline='Area %s' % i, pub_date=datetime(2005, 7, 28))
+            for i in range(max_results)
+        )
+        self.assertRaisesMessage(
+            MultipleObjectsReturned,
+            'get() returned more than one Article -- it returned %d!' % max_results,
+            Article.objects.get,
+            headline__startswith='Area',
+        )
+        Article.objects.create(headline='Area %s' % max_results, pub_date=datetime(2005, 7, 28))
+        self.assertRaisesMessage(
+            MultipleObjectsReturned,
+            'get() returned more than one Article -- it returned more than %d!' % max_results,
+            Article.objects.get,
+            headline__startswith='Area',
+        )
+
 
 class ModelLookupTest(TestCase):
     @classmethod