Add ModelTracker with tests

model_utils/models.py

@@ -3,7 +3,7 @@ from datetime import datetime
 from django.db import models
 from django.utils.translation import ugettext_lazy as _
 from django.db.models.fields import FieldDoesNotExist
-from django.core.exceptions import ImproperlyConfigured
+from django.core.exceptions import ImproperlyConfigured, FieldError
 
 from model_utils.managers import QueryManager
 from model_utils.fields import AutoCreatedField, AutoLastModifiedField, \
@@ -97,3 +97,79 @@ def add_timeframed_query_manager(sender, **kwargs):
 
 models.signals.class_prepared.connect(add_status_query_managers)
 models.signals.class_prepared.connect(add_timeframed_query_manager)
+
+
+class ModelTracker(object):
+    def __init__(self, fields=None):
+        self.fields = fields
+
+    def contribute_to_class(self, cls, name):
+        self.name = name
+        models.signals.class_prepared.connect(self.finalize, sender=cls)
+
+    def finalize(self, sender, **kwargs):
+        descriptor = ModelTrackerDescriptor(sender, self.name, self.fields)
+        setattr(sender, self.name, descriptor)
+
+
+class ModelTrackerDescriptor(object):
+    def __init__(self, cls, name, fields):
+        self.attname = '_%s' % name
+        self.fields = fields
+        if self.fields is None:
+            self.fields = [field.attname for field in cls._meta.local_fields]
+        models.signals.post_init.connect(self.initialize, sender=cls)
+
+    def initialize(self, sender, instance, **kwargs):
+        tracker = ModelInstanceTracker(instance, self.fields)
+        setattr(instance, self.attname, tracker)
+        tracker.set_saved_fields()
+        self.patch_save(instance)
+
+    def patch_save(self, instance):
+        original_save = instance.save
+        def save(**kwargs):
+            ret = original_save()
+            getattr(instance, self.attname).set_saved_fields()
+            return ret
+        setattr(instance, 'save', save)
+
+    def __get__(self, instance, owner):
+        if instance is None:
+            return self
+        else:
+            return getattr(instance, self.attname)
+
+
+class ModelInstanceTracker(object):
+    def __init__(self, instance, fields):
+        self.instance = instance
+        self.fields = fields
+
+    def set_saved_fields(self):
+        self.saved_data = self.current_fields()
+
+    def current_fields(self):
+        return (dict((f, getattr(self.instance, f)) for f in self.fields)
+                if self.instance.pk else {})
+
+    def has_changed(self, field):
+        """Returns ``True`` if field has changed from currently saved value"""
+        if not self.instance.pk:
+            return True
+        elif field in self.saved_data:
+            return self.saved_data.get(field) != getattr(self.instance, field)
+        else:
+            raise FieldError('field "%s" not tracked' % field)
+
+    def previous(self, field):
+        """Return currently saved value of given field"""
+        return self.saved_data.get(field)
+
+    def changed(self):
+        """Returns dict of fields that changed since save (with old values)"""
+        if not self.instance.pk:
+            return {}
+        saved = self.saved_data.iteritems()
+        current = self.current_fields()
+        return dict((k, v) for k, v in saved if v != current[k])

model_utils/tests/models.py

@@ -1,7 +1,7 @@
 from django.db import models
 from django.utils.translation import ugettext_lazy as _
 
-from model_utils.models import TimeStampedModel, StatusModel, TimeFramedModel
+from model_utils.models import TimeStampedModel, StatusModel, TimeFramedModel, ModelTracker
 from model_utils.managers import QueryManager, InheritanceManager, PassThroughManager
 from model_utils.fields import SplitField, MonitorField
 from model_utils import Choices
@@ -218,3 +218,17 @@ class Spot(models.Model):
     owner = models.ForeignKey(Dude, related_name='spots_owned')
 
     objects = PassThroughManager.for_queryset_class(SpotQuerySet)()
+
+
+class Tracked(models.Model):
+    name = models.CharField(max_length=20)
+    number = models.IntegerField()
+
+    tracker = ModelTracker()
+
+
+class TrackedNotDefault(models.Model):
+    name = models.CharField(max_length=20)
+    number = models.IntegerField()
+
+    name_tracker = ModelTracker(fields=['name'])

model_utils/tests/tests.py

@@ -6,7 +6,7 @@ from datetime import datetime, timedelta
 import django
 from django.db import models
 from django.db.models.fields import FieldDoesNotExist
-from django.core.exceptions import ImproperlyConfigured
+from django.core.exceptions import ImproperlyConfigured, FieldError
 from django.test import TestCase
 
 from model_utils import Choices
@@ -18,7 +18,8 @@ from model_utils.tests.models import (
     InheritanceManagerTestParent, InheritanceManagerTestChild1,
     InheritanceManagerTestChild2, TimeStamp, Post, Article, Status,
     StatusPlainTuple, TimeFrame, Monitored, StatusManagerAdded,
-    TimeFrameManagerAdded, Dude, SplitFieldAbstractParent, Car, Spot)
+    TimeFrameManagerAdded, Dude, SplitFieldAbstractParent, Car, Spot,
+    Tracked, TrackedNotDefault)
 
 
 
@@ -624,3 +625,110 @@ class CreatePassThroughManagerTests(TestCase):
 
     def test_related_manager_create(self):
         self.dude.spots_owned.create(name='The Crib', closed=True, secure=True)
+
+
+class ModelTrackerTestCase(TestCase):
+    def assertHasChanged(self, **kwargs):
+        for field, value in kwargs.iteritems():
+            if value is None:
+                self.assertRaises(FieldError, self.tracker.has_changed, field)
+            else:
+                self.assertEqual(self.tracker.has_changed(field), value)
+
+    def assertPrevious(self, **kwargs):
+        for field, value in kwargs.iteritems():
+            self.assertEqual(self.tracker.previous(field), value)
+
+    def assertChanged(self, **kwargs):
+        self.assertEqual(self.tracker.changed(), kwargs)
+
+    def update_instance(self, **kwargs):
+        for field, value in kwargs.iteritems():
+            setattr(self.instance, field, value)
+        self.instance.save()
+
+
+class ModelTrackerCommonTests(object):
+
+    def test_pre_save_has_changed(self):
+        self.assertHasChanged(name=True, number=True)
+        self.instance.name = 'new age'
+        self.assertHasChanged(name=True, number=True)
+
+    def test_pre_save_changed(self):
+        self.assertChanged()
+        self.instance.name = 'new age'
+        self.assertChanged()
+        self.instance.number = 8
+        self.assertChanged()
+        self.instance.name = ''
+        self.assertChanged()
+
+    def test_pre_save_previous(self):
+        self.assertPrevious(name=None, number=None)
+        self.instance.name = 'new age'
+        self.instance.number = 8
+        self.assertPrevious(name=None, number=None)
+
+
+class ModelTrackerTests(ModelTrackerTestCase, ModelTrackerCommonTests):
+    def setUp(self):
+        self.instance = Tracked()
+        self.tracker = self.instance.tracker
+
+    def test_post_save_has_changed(self):
+        self.update_instance(name='retro', number=4)
+        self.assertHasChanged(name=False, number=False)
+        self.instance.name = 'new age'
+        self.assertHasChanged(name=True, number=False)
+        self.instance.number = 8
+        self.assertHasChanged(name=True, number=True)
+        self.instance.name = 'retro'
+        self.assertHasChanged(name=False, number=True)
+
+    def test_post_save_previous(self):
+        self.update_instance(name='retro', number=4)
+        self.instance.name = 'new age'
+        self.assertPrevious(name='retro', number=4)
+
+    def test_post_save_changed(self):
+        self.update_instance(name='retro', number=4)
+        self.assertChanged()
+        self.instance.name = 'new age'
+        self.assertChanged(name='retro')
+        self.instance.number = 8
+        self.assertChanged(name='retro', number=4)
+        self.instance.name = 'retro'
+        self.assertChanged(number=4)
+
+
+class FieldTrackedModelCustomTests(ModelTrackerTestCase,
+                                   ModelTrackerCommonTests):
+    def setUp(self):
+        self.instance = TrackedNotDefault()
+        self.tracker = self.instance.name_tracker
+
+    def test_post_save_has_changed(self):
+        self.update_instance(name='retro', number=4)
+        self.assertHasChanged(name=False, number=None)
+        self.instance.name = 'new age'
+        self.assertHasChanged(name=True, number=None)
+        self.instance.number = 8
+        self.assertHasChanged(name=True, number=None)
+        self.instance.name = 'retro'
+        self.assertHasChanged(name=False, number=None)
+
+    def test_post_save_previous(self):
+        self.update_instance(name='retro', number=4)
+        self.instance.name = 'new age'
+        self.assertPrevious(name='retro', number=None)
+
+    def test_post_save_changed(self):
+        self.update_instance(name='retro', number=4)
+        self.assertChanged()
+        self.instance.name = 'new age'
+        self.assertChanged(name='retro')
+        self.instance.number = 8
+        self.assertChanged(name='retro')
+        self.instance.name = 'retro'
+        self.assertChanged()