Fixed QuerySet._fetch_all() executed prepare_objects() many times.

Author: iurisilvio

django_qserializer/serialization.py

@@ -107,8 +107,9 @@ def to_serialize(self, serializer=None):
         return self._serializer._prepare_queryset(self)
 
     def _fetch_all(self):
+        result_already_cached = self._result_cache is not None
         super()._fetch_all()
-        if not self._result_cache:
+        if result_already_cached or not self._result_cache:
             return
 
         serializer = self.serializer

django_qserializer/tests/test_serializer.py

@@ -1,3 +1,5 @@
+from unittest.mock import Mock
+
 import pytest
 
 from django_qserializer import BaseSerializer, serialize
@@ -205,3 +207,21 @@ def test_values(bus_fixture):
 
 def test_empty_result(db):
     Bus.objects.to_serialize(BaseSerializer).first()
+
+
+def test_fetch_all_idempotent(bus_fixture):
+    """
+    Regression test. `QuerySet._fetch_all` is called a lot of times and Django
+    execute queries once.
+    """
+    class S(BaseSerializer):
+        prepare_objects = Mock()
+
+    buses = Bus.objects.to_serialize(S).all()
+
+    list(buses)
+    S.prepare_objects.assert_called_once()
+
+    list(buses)
+    # The `prepare_objects` method was not called again.
+    S.prepare_objects.assert_called_once()

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = django_qserializer
-version = 0.2.7
+version = 0.2.8
 url = https://github.com/buserbrasil/django-qserializer
 license = MIT
 author = Iuri de Silvio