Receive only the last message on topics

Question

I have an application subscribed on Azure Servicebus Topic who is constantly receiving messages from Stream Analytics. But this application isn't every time subscribed on this Topic. How do I receive only the last message from the topic when the application do the subscription?

Messages are always proceeded as FIFO. Do you have multiple subscriptions into your topic ? What do you mean by "But this application isn't every time subscribed on this Topic" ? — Thomas, Sep 24 '16 at 09:08
It sounds like you have a case that is not exactly mapping to the ASB and some custom code might be required. Just like @Thomas said, could you elaborate on your app a bit more? — Sean Feldman, Sep 24 '16 at 15:10
@Thomas I have a subscriber application who sometimes is offline, when it goes online just need to receive the most recent message, not the entire queue of FIFO — Natan Valentim, Sep 26 '16 at 16:30
So what do you want to do with the other messages ? You ll need to clear you queue first (except the last message). — Thomas, Sep 26 '16 at 20:34

score 0 · Answer 1 · edited May 23 '17 at 12:15

Based on your question and your comments, this is what I can advice you:

When your application starts, connect to the Azure ServiceBus Subscription and get all messages in the queue.
Remove all the previous messages (just complete it) and process the last message.
Then you can start listening to new incoming messages.

Based on this answer (Clearing azure service bus queue in one go) :

// Get the message receiver
var messagingFactory = MessagingFactory.CreateFromConnectionString("ServiceBusConnectionString");
var messageReceiver = messagingFactory.CreateMessageReceiver(SubscriptionClient.FormatSubscriptionPath("TopicName", "SubscriptionName"));

BrokeredMessage lastMessage = null;
while (messageReceiver.Peek() != null)
{
    if(lastMessage != null)
    {
        // This was not the last message so complete it.
        lastMessage.Complete();
    }

    // Batch the receive operation
    var brokeredMessages = messageReceiver.ReceiveBatch(300).ToList();

    //Get the last message and remove it from the list
    lastMessage = brokeredMessages.Last();
    brokeredMessages.RemoveAt(brokeredMessages.Count -1);

    // Complete all the other messages
    var completeTasks = brokeredMessages.Select(m => Task.Run(() => m.Complete())).ToArray();

    // Wait for the tasks to complete. 
    Task.WaitAll(completeTasks);                
}

if (lastMessage != null)
{
    // Process your message 
}

// Start listening to new incoming message
messageReceiver.OnMessage(message =>
{
    // Process new messages
}, new OnMessageOptions());

Receive only the last message on topics

1 Answers1