Ticket #11007: model-instance-changes-v2.patch

tests/modeltests/changes/__init__.py

@@ +1 @@
+

tests/modeltests/changes/models.py

@@ +1 @@
+"""
+Detecting changes to an object
+
+The ``changes`` method of the django.models.Model class returns a dict
+{attribute: (old_value, new_value)} for all changed fields in a 
+model instance.
+"""
+
+from django.db import models
+
+class Person(models.Model):
+    name = models.CharField(max_length=20)
+    job = models.CharField(max_length=30)
+
+    def __unicode__(self):
+        return self.name
+
+__test__ = {'API_TESTS':"""
+>>> a = Person(name=u'Adrian', job=u'Hacker')
+>>> a.changes()
+{'job': (None, u'Hacker'), 'name': (None, u'Adrian')}
+>>> a.save()
+>>> a.changes()
+{}
+>>> a.name = u'Adrian H.'
+>>> a.changes()
+{'name': (u'Adrian', u'Adrian H.')}
+"""}

django/db/models/base.py

@@ -606 +606 @@
     def prepare_database_save(self, unused):
         return self.pk
 
+    def changes(self):
+        fields = [x.name for x in self._meta._fields() if not (x.name.endswith('_ptr_id') or x.name.endswith('_ptr'))]
+        if not self.pk:
+            return dict([(x, (None, getattr(self, x))) for x in fields if getattr(self,x) is not None])
+        old = self.__class__.objects.get(pk=self.pk)
+        return dict([(x, (getattr(old, x), getattr(self, x))) for x in fields if getattr(self, x) != getattr(old, x)])
+         
 
 ############################################
 # HELPER FUNCTIONS (CURRIED MODEL METHODS) #

docs/ref/models/instances.txt

@@ -200 +200 @@
    For more details, including how to delete objects in bulk, see
    :ref:`topics-db-queries-delete`.
 
+Changes to objects
+==================
+
+.. method:: Model.changes()
+
+Return a dict {atrribute_name: (old_value, new_value)} containing all
+attributes of the object that differ from the values stored in the database.
+For instances that have not yet been saved, all attributes with a value other
+than None are included and the old_value is set to None.
+
 .. _model-instance-methods:
 
 Other model instance methods