From ca46f4688cd609ec3a056fc4c66fb17176a9d712 Mon Sep 17 00:00:00 2001
From: Sergey Fedoseev <fedoseev.sergey@gmail.com>
Date: Tue, 8 Aug 2017 02:06:15 +0500
Subject: [PATCH] Refs #28459 -- Improved performance of
 SQLCompiler.results_iter().

---
 django/db/models/query.py        |  4 ++--
 django/db/models/sql/compiler.py | 28 +++++++++++++++-------------
 django/db/models/sql/query.py    |  2 +-
 3 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/django/db/models/query.py b/django/db/models/query.py
index c625da4bdc..0b65bb56e8 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -1227,9 +1227,9 @@ class RawQuerySet:
             converters = compiler.get_converters([
                 f.get_col(f.model._meta.db_table) if f else None for f in fields
             ])
+            if converters:
+                query = compiler.apply_converters(query, converters)
             for values in query:
-                if converters:
-                    values = compiler.apply_converters(values, converters)
                 # Associate fields to values
                 model_init_values = [values[pos] for pos in model_init_pos]
                 instance = model_cls.from_db(db, model_init_names, model_init_values)
diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index 5ae5213b14..d6caa34328 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -938,14 +938,17 @@ class SQLCompiler:
                     converters[i] = (convs, expression)
         return converters
 
-    def apply_converters(self, row, converters):
-        row = list(row)
-        for pos, (convs, expression) in converters.items():
-            value = row[pos]
-            for converter in convs:
-                value = converter(value, expression, self.connection)
-            row[pos] = value
-        return tuple(row)
+    def apply_converters(self, rows, converters):
+        connection = self.connection
+        converters = list(converters.items())
+        for row in rows:
+            row = list(row)
+            for pos, (convs, expression) in converters:
+                value = row[pos]
+                for converter in convs:
+                    value = converter(value, expression, connection)
+                row[pos] = value
+            yield tuple(row)
 
     def results_iter(self, results=None):
         """Return an iterator over the results from executing this query."""
@@ -953,11 +956,10 @@ class SQLCompiler:
             results = self.execute_sql(MULTI)
         fields = [s[0] for s in self.select[0:self.col_count]]
         converters = self.get_converters(fields)
-        for rows in results:
-            for row in rows:
-                if converters:
-                    row = self.apply_converters(row, converters)
-                yield row
+        rows = chain.from_iterable(results)
+        if converters:
+            rows = self.apply_converters(rows, converters)
+        return rows
 
     def has_results(self):
         """
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index bf21c66f20..1eb8598690 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -464,7 +464,7 @@ class Query:
             result = [None for q in outer_query.annotation_select.items()]
 
         converters = compiler.get_converters(outer_query.annotation_select.values())
-        result = compiler.apply_converters(result, converters)
+        result = next(compiler.apply_converters((result,), converters))
 
         return {
             alias: val