Fixed #24854 -- Refactored QuerySet._values

Added django.db.models.sql.query.Query.set_values() method to handle
query mutation.

django/db/models/query.py

@@ -681,42 +681,7 @@ class QuerySet(object):
     def _values(self, *fields):
         clone = self._clone()
         clone._fields = fields
-
-        query = clone.query
-        query.select_related = False
-        query.clear_deferred_loading()
-        query.clear_select_fields()
-
-        if query.group_by is True:
-            query.add_fields((f.attname for f in self.model._meta.concrete_fields), False)
-            query.set_group_by()
-            query.clear_select_fields()
-
-        if fields:
-            field_names = []
-            extra_names = []
-            annotation_names = []
-            if not query._extra and not query._annotations:
-                # Shortcut - if there are no extra or annotations, then
-                # the values() clause must be just field names.
-                field_names = list(fields)
-            else:
-                query.default_cols = False
-                for f in fields:
-                    if f in query.extra_select:
-                        extra_names.append(f)
-                    elif f in query.annotation_select:
-                        annotation_names.append(f)
-                    else:
-                        field_names.append(f)
-            query.set_extra_mask(extra_names)
-            query.set_annotation_mask(annotation_names)
-        else:
-            field_names = [f.attname for f in self.model._meta.concrete_fields]
-
-        query.values_select = field_names
-        query.add_fields(field_names, True)
-
+        clone.query.set_values(fields)
         return clone
 
     def values(self, *fields):

django/db/models/sql/query.py

@@ -1847,6 +1847,41 @@ class Query(object):
             self.extra_select_mask = set(names)
         self._extra_select_cache = None
 
+    def set_values(self, fields):
+        self.select_related = False
+        self.clear_deferred_loading()
+        self.clear_select_fields()
+
+        if self.group_by is True:
+            self.add_fields((f.attname for f in self.model._meta.concrete_fields), False)
+            self.set_group_by()
+            self.clear_select_fields()
+
+        if fields:
+            field_names = []
+            extra_names = []
+            annotation_names = []
+            if not self._extra and not self._annotations:
+                # Shortcut - if there are no extra or annotations, then
+                # the values() clause must be just field names.
+                field_names = list(fields)
+            else:
+                self.default_cols = False
+                for f in fields:
+                    if f in self.extra_select:
+                        extra_names.append(f)
+                    elif f in self.annotation_select:
+                        annotation_names.append(f)
+                    else:
+                        field_names.append(f)
+            self.set_extra_mask(extra_names)
+            self.set_annotation_mask(annotation_names)
+        else:
+            field_names = [f.attname for f in self.model._meta.concrete_fields]
+
+        self.values_select = field_names
+        self.add_fields(field_names, True)
+
     @property
     def annotation_select(self):
         """The OrderedDict of aggregate columns that are not masked, and should