How to get specified message from Azure Service Bus Topic and then delete it from Topic? - .net-core

Question

I’m writing functionality for receiving messages from Azure Service Bus Topic and delete the specified message from Topic. Before deleting that message, I need to send that message to other Topic.
static async Task ProcessMessagesAsync(Message message, CancellationToken token)
{
// Process the message.
Console.WriteLine($"Received message: WorkOrderNumber:{message.MessageId} SequenceNumber:{message.SystemProperties.SequenceNumber} Body:{Encoding.UTF8.GetString(message.Body)}");
Console.WriteLine("Enter the WorkOrder Number you want to delete:");
string WorkOrderNubmer = Console.ReadLine();
if (message.MessageId == WorkOrderNubmer)
{
//TODO:Post message into other topic(Priority) then delete from this current topic.
var status=await SendMessageToBus(message);
if (status == true)
{
await normalSubscriptionClient.CompleteAsync(message.SystemProperties.LockToken);
Console.WriteLine($"Successfully deleted your message from Topic:{NormalTopicName}-WorkOrderNumber:" + message.MessageId);
}
else
{
Console.WriteLine($"Failed to send message to PriorityTopic:{PriorityTopicName}-WorkOrderNumber:" + message.MessageId);
}
}
else
{
Console.WriteLine($"Failed to delete your message from Topic:{NormalTopicName}-WorkOrderNumber:" + WorkOrderNubmer);
// Complete the message so that it is not received again.
// This can be done only if the subscriptionClient is created in ReceiveMode.PeekLock mode (which is the default).
await normalSubscriptionClient.CompleteAsync(message.SystemProperties.LockToken);
// Note: Use the cancellationToken passed as necessary to determine if the subscriptionClient has already been closed.
// If subscriptionClient has already been closed, you can choose to not call CompleteAsync() or AbandonAsync() etc.
// to avoid unnecessary exceptions.
}
}
My issue with this approach is:
It’s not scalable; what if the message is the 50th in the collection? We’d have to iterate through 49 times and mark i.e deleted.
It’s a long-running process.
To avoid these problems, I want to get the specified message from the queue based on Index or sequence number then I can delete that from the topic.
So, can anyone suggest me how to resolve this problem?

Answer 1

So if I understand your questions and comments correctly you are trying to do something like this:
Incoming messages come into either a standard topic or priority
topic.
Some process checks messages in the standard topic and
"moves" them to the priority topic based on some criteria by
deleting them from the standard topic and adding them to the
priority topic.
Messages are processed as normal.
As Sean noted, step 2 simply won't work. Service Bus is a first=in-first-out-ish system where a consumer simply picks up the next available message. You can sort through a queue by pulling out all the messages and abandoning/completing them based on specific criteria, but scaling is a problem. In addition, you can think of each topic subscription as its own separate queue- removing a message form one subscription does not remove it from any of the other subscriptions.
What I would suggest instead of trying to pull out everything from the topics and then putting back the ones you want to keep, add a sorting queue in front of the two topics. If you don't need to sort the high priority messages you could put this sorting process in front of the standard priority topic only.
This is how the process would work:
Incoming messages are added to a sorting queue Note that this is a single queue, not a topic. At this point in the process we want to ensure there is only one copy of each message.
A sorting process moves messages from the sorting queue into either the standard or priority queue as is appropriate. Using something like Azure Functions you can scale this process fairly easily.
Messages are processed from the topics as normal.