Azure Service Bus Topic subscription with dynamic sql filter query

Question

I am trying to use Azure service bus to pass messages between multiple azure functions. I am creating topic and subscription in code. But not sure how to add filter query from code. I want to filter messages by id . e.g SqlFilter($"'id' ='{id}'") . I don't want to create one subscription for each message because of this filter.

Is it possible to have different filter for a subscription?

This issue can be fixed by creating one subscription for each request and deleting it afterwards. But i don't want to create so many subscriptions. My aim is to just change the filter each time the function is called.

Sample code:

var connectionString = ConfigurationManager.AppSettings["ServiceBus_CONNECTION_STRING"];
                var namespaceManager =
                    NamespaceManager.CreateFromConnectionString(connectionString);
                if (!await namespaceManager.TopicExistsAsync(topicName))
                {
                    // Configure Topic Settings.
                    var topic = new TopicDescription(topicName)
                    {
                        MaxSizeInMegabytes = 1024,
                        DefaultMessageTimeToLive = TimeSpan.FromMinutes(5)
                    };

                    await namespaceManager.CreateTopicAsync(topic);
                }

                if (!await namespaceManager.SubscriptionExistsAsync(topicName, subscription))
                {
                    await namespaceManager.CreateSubscriptionAsync(topicName, subscription);
                }

                var cts = new TaskCompletionSource<T>();
                var subClient =
                    SubscriptionClient.CreateFromConnectionString(connectionString, topicName,
                        subscription);

                var ruleDescription = new RuleDescription($"RequestIdRule{id}", new SqlFilter($"'id' ='{id}'"));

                await subClient.AddRuleAsync(ruleDescription);
                var options = new OnMessageOptions();

                subClient.OnMessage(m =>
                    {
                        try
                        {

                            var body = m.GetBody<T>();
                            cts.SetResult(body);
                        }
                        catch (Exception ex)
                        {

                            m.Abandon();
                        }
                    },
                    options);

                return await cts.Task;

            }
            catch (Exception ex)
            {
                throw;
            }

Sean Feldman Sean Feldman · Accepted Answer · 2017-10-03T00:11:03

Is it possible to have different filter for a subscription?

Yes. A single topics with all its subscriptions can have up to 2,000 SQL filters (100,000 for correlation filters). See documentation here.

You can't update a filter. You'd need to delete the old rule and replace it with a new one by creating one. But I question the efficiency of this approach if you do it frequently at run-time.

I am trying to use Azure service bus to pass messages between multiple azure functions.

Alternatively, you could have each function have its input queue, where chaining those functions would be sending a message to the appropriate Azure Service Bus input queue.

And finally,

My aim is to just change the filter each time the function is called.

If you have a spike of messages, your function would be scaled out. That means, you could execute the same function for different messages. Each message would require creation of a different rule under the same subscription. Not only it feels off, but it will create a contention over the subscription to update the rule which will lead to either a failure or incorrect behavior.

Azure Service Bus Topic subscription with dynamic sql filter query

1 Answers