add LWTException when insertion is not applied.

cqlengine/exceptions.py

@@ -4,3 +4,4 @@ class ModelException(CQLEngineException): pass
 class ValidationError(CQLEngineException): pass
 
 class UndefinedKeyspaceException(CQLEngineException): pass
+class LWTException(CQLEngineException): pass

cqlengine/query.py

@@ -6,7 +6,7 @@ from cqlengine.columns import Counter, List, Set
 
 from cqlengine.connection import execute
 
-from cqlengine.exceptions import CQLEngineException, ValidationError
+from cqlengine.exceptions import CQLEngineException, ValidationError, LWTException
 from cqlengine.functions import Token, BaseQueryFunction, QueryValue, UnicodeMixin
 
 #CQL 3 reference:
@@ -22,6 +22,17 @@ class MultipleObjectsReturned(QueryException): pass
 
 import six
 
+
+def check_applied(result):
+    """
+    check if result contains some column '[applied]' with false value,
+    if that value is false, it means our light-weight transaction didn't
+    applied to database.
+    """
+    if result and '[applied]' in result[0] and result[0]['[applied]'] == False:
+        raise LWTException('')
+
+
 class AbstractQueryableColumn(UnicodeMixin):
     """
     exposes cql query operators through pythons
@@ -171,7 +182,8 @@ class BatchQuery(object):
 
         query_list.append('APPLY BATCH;')
 
-        execute('\n'.join(query_list), parameters, self._consistency)
+        tmp = execute('\n'.join(query_list), parameters, self._consistency)
+        check_applied(tmp)
 
         self.queries = []
         self._execute_callbacks()
@@ -790,6 +802,9 @@ class DMLQuery(object):
             return self._batch.add_query(q)
         else:
             tmp = execute(q, consistency_level=self._consistency)
+            if self._if_not_exists:
+                check_applied(tmp)
+ 
             return tmp
 
     def batch(self, batch_obj):

cqlengine/tests/test_ifnotexists.py

@@ -2,9 +2,9 @@ from unittest import skipUnless
 from cqlengine.management import sync_table, drop_table, create_keyspace, delete_keyspace
 from cqlengine.tests.base import BaseCassEngTestCase
 from cqlengine.models import Model
+from cqlengine.exceptions import LWTException
 from cqlengine import columns, BatchQuery
 from uuid import uuid4
-from datetime import datetime
 import mock
 from cqlengine.connection import get_cluster
 
@@ -50,7 +50,10 @@ class IfNotExistsInsertTests(BaseIfNotExistsTest):
         id = uuid4()
 
         TestIfNotExistsModel.create(id=id, count=8, text='123456789')
-        TestIfNotExistsModel.if_not_exists().create(id=id, count=9, text='111111111111')
+        self.assertRaises(
+            LWTException,
+            TestIfNotExistsModel.if_not_exists().create, id=id, count=9, text='111111111111'
+            )
 
         q = TestIfNotExistsModel.objects(id=id)
         self.assertEqual(len(q), 1)
@@ -83,8 +86,9 @@ class IfNotExistsInsertTests(BaseIfNotExistsTest):
         with BatchQuery() as b:
             TestIfNotExistsModel.batch(b).if_not_exists().create(id=id, count=8, text='123456789')
 
-        with BatchQuery() as b:
+        b = BatchQuery()
-            TestIfNotExistsModel.batch(b).if_not_exists().create(id=id, count=9, text='111111111111')
+        TestIfNotExistsModel.batch(b).if_not_exists().create(id=id, count=9, text='111111111111')
+        self.assertRaises(LWTException, b.execute)
 
         q = TestIfNotExistsModel.objects(id=id)
         self.assertEqual(len(q), 1)

docs/topics/models.rst

@@ -194,6 +194,17 @@ Model Methods
         object is determined by its primary key(s). And please note using this flag
         would incur performance cost.
 
+        if the insertion didn't applied, a LWTException exception would be raised.
+
+        *Example*
+
+        .. code-block:: python
+            try:
+                TestIfNotExistsModel.if_not_exists().create(id=id, count=9, text='111111111111')
+            except LWTException as e:
+                # handle failure case
+                print e.existing # existing object
+
         This method is supported on Cassandra 2.0 or later.
 
     .. method:: update(**values)