Add an ExecuteLastObjectDataManager that attempts to execute after ot…

src/nti/transactions/tests/test_transaction.py

@@ -12,17 +12,22 @@
 #pylint: disable=W0212,R0904
 
 import unittest
+
 from hamcrest import assert_that
 from hamcrest import is_
 from hamcrest import calling
 from hamcrest import raises
+from hamcrest import contains
 
 import fudge
 
-from ..transactions import _do_commit
-from ..transactions import TransactionLoop
-from ..interfaces import CommitFailedError
-from ..interfaces import AbortFailedError
+from nti.transactions.interfaces import CommitFailedError
+from nti.transactions.interfaces import AbortFailedError
+
+from nti.transactions.transactions import do
+from nti.transactions.transactions import do_near_end
+from nti.transactions.transactions import _do_commit
+from nti.transactions.transactions import TransactionLoop
 
 import transaction
 from transaction.interfaces import TransientError
@@ -218,3 +223,19 @@ def handler():
 
         loop = Loop(handler)
         assert_that(calling(loop), raises(AbortFailedError))
+
+class TestDataManagers(unittest.TestCase):
+
+    def test_data_manager_sorting(self):
+        results = []
+        def test_call(x):
+            results.append(x)
+
+        # The managers will execute in order added (since identical),
+        # except for the one that requests to go last.
+        manager1 = do(call=test_call, args=(0,))
+        manager2 = do(call=test_call, args=(1,))
+        manager_post = do_near_end(call=test_call, args=(10,))
+        manager3 = do(call=test_call, args=(2,))
+        transaction.commit()
+        assert_that(results, contains(0,1,2,10))

src/nti/transactions/transactions.py

@@ -196,6 +196,22 @@ def rollback(self):
         # anyway.
         pass
 
+class OrderedNearEndObjectDataManager(ObjectDataManager):
+    """
+    A special extension of :class:`ObjectDataManager` that attempts to execute
+    after all other data managers have executed. This is useful when an
+    operation relies on the execution of other data managers.
+    """
+
+    def sortKey(self):
+        """
+        Sort prepended with z's in an attempt to execute after other data
+        managers.
+        """
+        parent_key = super(OrderedNearEndObjectDataManager, self).sortKey()
+        sort_str = str(self.target) if self.target is not None else str(self.callable)
+        return 'zzz%s:%s' % (sort_str, parent_key)
+
 class _QueuePutDataManager(ObjectDataManager):
     """
     A data manager that checks if the queue is full before putting.
@@ -233,10 +249,20 @@ def do(*args, **kwargs):
     Establishes a IDataManager in the current transaction.
     See :class:`ObjectDataManager` for the possible arguments.
     """
-    result = ObjectDataManager(*args, **kwargs)
+    klass = kwargs.pop('datamanager_class', ObjectDataManager)
+    result = klass(*args, **kwargs)
     transaction.get().join(result)
     return result
 
+def do_near_end(*args, **kwargs):
+    """
+    Establishes a IDataManager in the current transaction that will attempt to
+    execute *after* all other DataManagers have had their say.
+    See :class:`ObjectDataManager` for the possible arguments.
+    """
+    kwargs['datamanager_class'] = OrderedNearEndObjectDataManager
+    return do(*args, **kwargs)
+
 def _do_commit(tx, description, long_commit_duration):
     exc_info = sys.exc_info()
     try: