adding method for determining which column values have changed

cqlengine/models.py

@@ -409,6 +409,10 @@ class BaseModel(object):
         """ Deletes this instance """
         self.__dmlquery__(self.__class__, self, batch=self._batch).delete()
 
+    def get_changed_columns(self):
+        """ returns a list of the columns that have been updated since instantiation or save """
+        return [k for k,v in self._values.items() if v.changed]
+
     @classmethod
     def _class_batch(cls, batch):
         return cls.objects.batch(batch)

cqlengine/tests/model/test_model_io.py

@@ -42,8 +42,6 @@ class TestModelIO(BaseCassEngTestCase):
         for cname in tm._columns.keys():
             self.assertEquals(getattr(tm, cname), getattr(tm2, cname))
 
-
-
     def test_model_updating_works_properly(self):
         """
         Tests that subsequent saves after initial model creation work
@@ -78,7 +76,6 @@ class TestModelIO(BaseCassEngTestCase):
         assert tm2.text is None
         assert tm2._values['text'].previous_value is None
 
-
     def test_a_sensical_error_is_raised_if_you_try_to_create_a_table_twice(self):
         """
         """
@@ -92,6 +89,7 @@ class TestMultiKeyModel(Model):
     count       = columns.Integer(required=False)
     text        = columns.Text(required=False)
 
+
 class TestDeleting(BaseCassEngTestCase):
 
     @classmethod
@@ -158,6 +156,14 @@ class TestUpdating(BaseCassEngTestCase):
         assert check.count is None
         assert check.text is None
 
+    def test_get_changed_columns(self):
+        assert self.instance.get_changed_columns() == []
+        self.instance.count = 1
+        changes = self.instance.get_changed_columns()
+        assert len(changes) == 1
+        assert changes == ['count']
+        self.instance.save()
+        assert self.instance.get_changed_columns() == []
 
 
 class TestCanUpdate(BaseCassEngTestCase):

docs/topics/models.rst

@@ -137,6 +137,7 @@ Model Methods
     .. method:: delete()
 
         Deletes the object from the database.
+
     -- method:: update(**values)
 
 
@@ -145,6 +146,10 @@ Model Methods
         fields. If no fields on the model have been modified since loading, no query will be
         performed. Model validation is performed normally.
 
+    -- method:: get_changed_columns()
+
+        Returns a list of column names that have changed since the model was instantiated or saved
+
 Model Attributes
 ================