azure - 仅接收有关主题的最后一条消息

Question

我在 Azure Servicebus 主题上订阅了一个应用程序，该应用程序不断从流分析接收消息。但该应用程序并非每次都订阅该主题。当应用程序进行订阅时，如何仅接收来自主题的最后一条消息？

Answer 1

根据您的问题和评论，我可以向您提供以下建议:

• 当应用程序启动时，连接到 Azure ServiceBus 订阅并获取队列中的所有消息。
• 删除之前的所有消息(只需完成即可)并处理最后一条消息。
• 然后您就可以开始收听新收到的消息。

基于这个答案(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());