From 041ef6b8388f4b87ffe5733568d05550c61bdd29 Mon Sep 17 00:00:00 2001
From: bboogaard <b.boogaard@auto-interactive.nl>
Date: Tue, 19 Aug 2014 10:20:33 +0200
Subject: [PATCH] Keep track of deferred fields on model instance

Instead of on FieldInstanceTracker instance

Signed-off-by: bboogaard <b.boogaard@auto-interactive.nl>
---
 model_utils/tests/tests.py | 20 +++++++++++++++++---
 model_utils/tracker.py     | 10 +++++-----
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/model_utils/tests/tests.py b/model_utils/tests/tests.py
index 38150a8..bbacfd1 100644
--- a/model_utils/tests/tests.py
+++ b/model_utils/tests/tests.py
@@ -1485,13 +1485,13 @@ class FieldTrackerTests(FieldTrackerTestCase, FieldTrackerCommonTests):
         self.instance.number = 1
         self.instance.save()
         item = list(self.tracked_class.objects.only('name').all())[0]
-        self.assertTrue(item.tracker.deferred_fields)
+        self.assertTrue(item._deferred_fields)
 
         self.assertEqual(item.tracker.previous('number'), None)
-        self.assertTrue('number' in item.tracker.deferred_fields)
+        self.assertTrue('number' in item._deferred_fields)
 
         self.assertEqual(item.number, 1)
-        self.assertTrue('number' not in item.tracker.deferred_fields)
+        self.assertTrue('number' not in item._deferred_fields)
         self.assertEqual(item.tracker.previous('number'), 1)
         self.assertFalse(item.tracker.has_changed('number'))
 
@@ -1499,6 +1499,20 @@ class FieldTrackerTests(FieldTrackerTestCase, FieldTrackerCommonTests):
         self.assertTrue(item.tracker.has_changed('number'))
 
 
+class FieldTrackerMultipleInstancesTests(TestCase):
+
+    def test_with_deferred_fields_access_multiple(self):
+        instances = [
+            Tracked.objects.create(pk=1, name='foo', number=1),
+            Tracked.objects.create(pk=2, name='bar', number=2)
+        ]
+
+        queryset = Tracked.objects.only('id')
+
+        for instance in queryset:
+            name = instance.name
+
+
 class FieldTrackedModelCustomTests(FieldTrackerTestCase,
                                    FieldTrackerCommonTests):
 
diff --git a/model_utils/tracker.py b/model_utils/tracker.py
index 6cb4355..be5a7ff 100644
--- a/model_utils/tracker.py
+++ b/model_utils/tracker.py
@@ -32,10 +32,10 @@ class FieldInstanceTracker(object):
     def current(self, fields=None):
         """Returns dict of current values for all tracked fields"""
         if fields is None:
-            if self.deferred_fields:
+            if self.instance._deferred_fields:
                 fields = [
                     field for field in self.fields
-                    if field not in self.deferred_fields
+                    if field not in self.instance._deferred_fields
                 ]
             else:
                 fields = self.fields
@@ -62,7 +62,7 @@ class FieldInstanceTracker(object):
         )
 
     def init_deferred_fields(self):
-        self.deferred_fields = []
+        self.instance._deferred_fields = []
         if not self.instance._deferred:
             return
 
@@ -70,7 +70,7 @@ class FieldInstanceTracker(object):
             def __get__(field, instance, owner):
                 data = instance.__dict__
                 if data.get(field.field_name, field) is field:
-                    self.deferred_fields.remove(field.field_name)
+                    instance._deferred_fields.remove(field.field_name)
                     value = super(DeferredAttributeTracker, field).__get__(
                         instance, owner)
                     self.saved_data[field.field_name] = deepcopy(value)
@@ -79,7 +79,7 @@ class FieldInstanceTracker(object):
         for field in self.fields:
             field_obj = self.instance.__class__.__dict__.get(field)
             if isinstance(field_obj, DeferredAttribute):
-                self.deferred_fields.append(field)
+                self.instance._deferred_fields.append(field)
 
                 # Django 1.4
                 model = None