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4.5. Transactions

The WCF channel provides a transaction resource manager module and a recovery module that together provide distributed transaction support with one-phase optimization. Some configuration is required on Windows machines to enable transaction support (see your installation notes or top level ReadMe.txt file for instructions). Once properly configured, the Qpid WCF channel acts as any other System.Transactions aware resource, capable of participating in explicit or implicit transactions.

Server code:

[OperationBehavior(TransactionScopeRequired = true,
                   TransactionAutoComplete = true)]

public void SayHello(string greeting)
{
  // increment ExactlyOnceReceived counter on DB

  // Success: transaction auto completes:
}

Because this operation involves two transaction resources, the database and the AMQP message broker, this operates as a full two phase commit transaction managed by the Distributed Transaction Coordinator service. If the transaction proceeds without error, both ExactlyOnceReceived is incremented in the database and the AMQP message is consumed from the broker. Otherwise, ExactlyOnceReceived is unchanged and AMQP message is returned to its queue on the broker.

For the client code a few changes are made to the non-transacted example. For "exactly once" semantics, we set the AMQP "Durable" message property and enclose the transacted activities in a TransactionScope:

AmqpProperties myDefaults = new AmqpProperties();
myDefaults.Durable = true;
amqpBinding.DefaultMessageProperties = myDefaults;
ChannelFactory<IHelloService> channelFactory =
new ChannelFactory<IHelloService>(amqpBinding, clientEndpoint);
IHelloService clientProxy = channelFactory.CreateChannel();

using (TransactionScope ts = new TransactionScope())
{
   AmqpProperties amqpProperties = new AmqpProperties();
   clientProxy.SayHello("Greetings from WCF client");
   // increment ExactlyOnceSent counter on DB
   ts.Complete();
}