Nservice总线Sagas实现

Question

I have a nservice bus project which which i will call connector. My connector receives variouis kinds of messages for example ClientChangeMessage, ClientContactChangeMessage. My connector has not implemented saga so i have handler for each message so for ClientChangeMessage I have ClientChangeMessageHandler which gets fired when connector receives ClientChangeMessage and a ClientContactChangeMessageHandler when i receive a ClientContactChangeMessage.

Now while looking at the sagas implementation i found myself writing the following code (If the Client contact message comes before the ClientChange message ie the client does not exist in the database):

public class ClientContactChangeMessageHandler : ClientMessageHandler, 
    IHandleMessages<ClientContactChangeMessage>, 
    IAmStartedByMessages<ClientContactChangeMessage>, 
    IHandleMessages<ClientChangeMessage>
{
    [SetterProperty]
    public IClientContactChangeDb ClientContactChangeDb{get;set;}

    [SetterProperty]
    public IBusRefTranslator BusRefTranslator{get;set;}

    static ClientContactChangeMessageHandler()
    {
        Logger = LogManager.GetLogger(typeof (ClientContactChangeMessageHandler));
    }

    static ILog Logger;

    public void Handle(ClientContactChangeMessage message)
    {
        //Some handling logic
    }

    public void Handle(ClientChangeMessage message)
    {
        throw new NotImplementedException();
    }

    public override void ConfigureHowToFindSaga()
    {
        ConfigureMapping<ClientContactChangeMessage>(s => s.Id, m => m.Id);
        ConfigureMapping<ClientChangeMessage>(s => s.Id, m => m.Id);
        // Notice that we have no mappings for the OrderAuthorizationResponseMessage message. This is not needed since the HR
        // endpoint will do a Bus.Reply and NServiceBus will then automatically correlate the reply back to
        // the originating saga
    }
}


public class ClientMessageHandler : BaseMessageHandler
{
}

public class BaseMessageHandler : Saga<MySagaData>
{
}

public class MySagaData : IContainSagaData
{
    public Guid Id { get; set; }
    public string Originator { get; set; }
    public string OriginalMessageId { get; set; }
}

As can be seen from the example I now have to implement the handle for the CLientChangeMessage as well , now i have already defined a handler for my ClientChangeMessage ,do i have to handle it again over here because if further on in time the ClientChangeMessage does come i would expect it to be caught and processed by the ClientChangeMessageHandler nad not by this one.

I would like to store a message if and only if i don't find the local reference for the Client in my database . Looking at the examples for saga on the web i dont't see any particular place or condition where this would be handled. I am hoping i would be storing the message inside the ClientContactChange handle method.

Any help would be much appreciated,

Thanks

UPDATE:

It would seem that i did not understand properly how to implement NService Bus Saga. The mistake which i made here according to me was that I considered A Client Contact change to be a single entity ie independent of the Client Change message. So therefore i think i ma wrong in implementing the Saga just for client contact change . Here is how I had to change my code:

 public class ClientSaga : Saga<ClientSagaState>, 
        IAmStartedByMessages<ClientChangeMessage>, 
        IAmStartedByMessages<ClientContactChangeMessage>, 
        IHandleTimeout<ClientSagaState>
    {
        [SetterProperty]
        public IClientContactChangeDb ClientContactChangeDb{get;set;}

        [SetterProperty]
        public IBusRefTranslator BusRefTranslator{get;set;}



        public void Handle(ClientContactChangeMessage message)
        {
            //Some handling logic
            //Check if client is not in database then store the state
            this.ClientContactChange=message;
            //if client is in the data base then 
            MarkAsComplete();
        }

        public void Handle(ClientChangeMessage message)
        {
            //Update or create the client depending on the situation
            //check for dependencies
            if(this.ClientContactChange !=null)
            {
                 //Handle the contact change
            }
        }

        public override void ConfigureHowToFindSaga()
        {
            ConfigureMapping<ClientContactChangeMessage>(s => s.ClientRef, m => m.ClientRef);
            ConfigureMapping<ClientChangeMessage>(s => s.ClienttnRef, m => m.Id);
            // Notice that we have no mappings for the OrderAuthorizationResponseMessage message. This is not needed since the HR
            // endpoint will do a Bus.Reply and NServiceBus will then automatically correlate the reply back to
            // the originating saga
        }
    }


    public class ClientSagaState: IContainSagaData
    {
        //i dont need these three fields
        public Guid Id { get; set; }
        public string Originator { get; set; }
        public string OriginalMessageId { get; set; }

       // the fields which i needed
       public Guid ClientRef {gee; set;}
       public ClientChangeMessage ClientChange {get;set;}
       public ClientContactChange ClientContactChange {get;set;}

    }

Answer 1

Since both handlers handle the same message type, both will be called. If you like you could specify the order in which they get called using ISpecifyMessageHandlerOrdering. Furthermore, you can short circuit this chain based on a condition which may solve the secondary issue.

If that does not work, you may want to consider versioning the message to support both scenarios in a graceful way.