How to get queue message type - azure

Question

I'm using Azure Storage Queues and I want to write some code that retrieves all queues, and then finds a handler that can process the message in this queue. For that I defined an interface like this:
public interface IHandler<T>
I have multiple implementations of this interface, like these: IHandler<CreateAccount> or IHandler<CreateOrder>. I use 1 queue per message type, so the CreateAccount messages would go into the create-account-queue.
How do I hook these up? In order to find the right Handler class for a message, I first need to know the message type, but it seems that CloudQueueMessage objects don't contain that information.

Answer 1

Not really an answer to your question but I will share how we're handling exact same situation in our application.
In our application, we're sending different kinds of messages like you are and handling those messages in a background process.
What we're doing is including the message type in the message body itself. So our message typically looks like:
message: {
type: 'Type Of Message',
contents: {
//Message contents
}
}
One key difference is that all messages go in a single queue (instead of different queues in your case). The receiver (background process) just polls one queue, gets the message and identifies the type of message and call handler for that message accordingly.

Answer 2

You can associate metadata with each queue. Since you mentioned that you use one queue per message type, you could put the handler name in the metadata for each queue. You can then enumerate all queues and get the metadata per queue that tells you what type of handler you should use. Here's a quick console app that demonstrates what I think you're asking for:
using System;
using System.Collections.Generic;
using Microsoft.WindowsAzure.Storage;
using Microsoft.WindowsAzure.Storage.Queue;
namespace QueueDemo
{
class Program
{
static void Main(string[] args)
{
//get a ref to our account.
CloudStorageAccount storageAccount = CloudStorageAccount.Parse("UseDevelopmentStorage=true;");
CloudQueueClient cloudQueueClient = storageAccount.CreateCloudQueueClient();
//create our queues and add metadata showing what type of class each queue contains.
CloudQueue queue1 = cloudQueueClient.GetQueueReference("queue1");
queue1.Metadata.Add("classtype", "classtype1");
queue1.CreateIfNotExists();
CloudQueue queue2 = cloudQueueClient.GetQueueReference("queue2");
queue2.Metadata.Add("classtype", "classtype2");
queue2.CreateIfNotExists();
//enumerate our queues in a storage account and look at their metadata...
QueueContinuationToken token = null;
List<CloudQueue> cloudQueueList = new List<CloudQueue>();
List<string> queueNames = new List<string>();
do
{
QueueResultSegment segment = cloudQueueClient.ListQueuesSegmented(token);
token = segment.ContinuationToken;
cloudQueueList.AddRange(segment.Results);
}
while (token != null);
try
{
foreach (CloudQueue cloudQ in cloudQueueList)
{
//call this, or else your metadata won't be included for the queue.
cloudQ.FetchAttributes();
Console.WriteLine("Cloud Queue name = {0}, class type = {1}", cloudQ.Name, cloudQ.Metadata["classtype"]);
queueNames.Add(cloudQ.Name);
}
}
catch (Exception ex)
{
Console.WriteLine("Exception thrown listing queues: " + ex.Message);
throw;
}
//clean up after ourselves and delete queues.
foreach (string oneQueueName in queueNames)
{
CloudQueue cloudQueue = cloudQueueClient.GetQueueReference(oneQueueName);
cloudQueue.DeleteIfExists();
}
Console.ReadKey();
}
}
}
However, it might be easier to subclass QueueMessage, then dequeue each message and identify what subclass you're currently looking at, then pass it to the proper handler.