From dca67bb2c27cfa1b23cb6519c544ce467813e0ec Mon Sep 17 00:00:00 2001
From: Sergey Fedoseev <fedoseev.sergey@gmail.com>
Date: Thu, 24 Aug 2017 01:26:24 +0500
Subject: [PATCH] Refs #28459 -- Improved performance of
 SQLCompiler.apply_converters().

---
 django/db/models/query.py        | 5 ++---
 django/db/models/sql/compiler.py | 9 +++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/django/db/models/query.py b/django/db/models/query.py
index 2a53fa3e89..512ebad784 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -119,7 +119,6 @@ class ValuesListIterable(BaseIterable):
         query = queryset.query
         compiler = query.get_compiler(queryset.db)
 
-        results = compiler.results_iter()
         if queryset._fields:
             field_names = list(query.values_select)
             extra_names = list(query.extra_select)
@@ -133,8 +132,8 @@ class ValuesListIterable(BaseIterable):
                 # Reorder according to fields.
                 index_map = {name: idx for idx, name in enumerate(names)}
                 rowfactory = operator.itemgetter(*[index_map[f] for f in fields])
-                results = map(rowfactory, results)
-        return results
+                return map(rowfactory, compiler.results_iter())
+        return compiler.results_iter(tuple_expected=True)
 
 
 class FlatValuesListIterable(BaseIterable):
diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index f92df8c996..2afc3635fa 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -942,16 +942,15 @@ class SQLCompiler:
     def apply_converters(self, rows, converters):
         connection = self.connection
         converters = list(converters.items())
-        for row in rows:
-            row = list(row)
+        for row in map(list, rows):
             for pos, (convs, expression) in converters:
                 value = row[pos]
                 for converter in convs:
                     value = converter(value, expression, connection)
                 row[pos] = value
-            yield tuple(row)
+            yield row
 
-    def results_iter(self, results=None):
+    def results_iter(self, results=None, tuple_expected=False):
         """Return an iterator over the results from executing this query."""
         if results is None:
             results = self.execute_sql(MULTI)
@@ -960,6 +959,8 @@ class SQLCompiler:
         rows = chain.from_iterable(results)
         if converters:
             rows = self.apply_converters(rows, converters)
+            if tuple_expected:
+                rows = map(tuple, rows)
         return rows
 
     def has_results(self):