Prefetching the user object when getting the token in TokenAuthentication.

Since the user object is fetched 4 lines after getting Token from the database, this removes a DB query for each token-authenticated request.

rest_framework/authentication.py

@@ -167,7 +167,7 @@ class TokenAuthentication(BaseAuthentication):
 
     def authenticate_credentials(self, key):
         try:
-            token = self.model.objects.get(key=key)
+            token = self.model.objects.select_related('user').get(key=key)
         except self.model.DoesNotExist:
             raise exceptions.AuthenticationFailed('Invalid token')
 

tests/test_authentication.py

@@ -202,6 +202,12 @@ class TokenAuthTests(TestCase):
         response = self.csrf_client.post('/token/', {'example': 'example'}, format='json', HTTP_AUTHORIZATION=auth)
         self.assertEqual(response.status_code, status.HTTP_200_OK)
 
+    def test_post_json_makes_one_db_query(self):
+        """Ensure that authenticating a user using a token performs only one DB query"""
+        auth = "Token " + self.key
+        func_to_test = lambda: self.csrf_client.post('/token/', {'example': 'example'}, format='json', HTTP_AUTHORIZATION=auth)
+        self.assertNumQueries(1, func_to_test)
+
     def test_post_form_failing_token_auth(self):
         """Ensure POSTing form over token auth without correct credentials fails"""
         response = self.csrf_client.post('/token/', {'example': 'example'})