Auto Subscriber

From v0.7.1.30 EasyNetQ comes with a simple AutoSubscriber. You can use it to easily scan a specific assembly for classes that implements the interface IConsume<T>, and then let the auto subscriber subscribe these consumers to your bus. You can of course let your consumers handle multiple messages. Lets have a look at some samples.

Lets define a simple consumer, handling two messages: MessageA and MessageB.

public class MyConsumer : IConsume<MessageA>, IConsume<MessageB>
{
    public void Consume(MessageA message) { }

    public void Consume(MessageB message) { }
}

To register this, and all other consumers in the same Assembly, we just need to pass the assembly to: AutoSubscriber.Subscribe(assembly). Note! This is something you only should do ONCE. Preferably where you configure your runtime, e.g. where you bootstrap your IoC-container.

var subscriber = new AutoSubscriber(bus);
subscriber.Subscribe(Assembly.GetExecutingAssembly());

Hook In Your IoC-Container

By default the AutoSubscriber requires you to have a default, parameter less constructor. You probably want to hook in your IoC-container instead, to let it control how the actual instances of your consumers are created; in our case, the MyConsumer.

If we would introduce a constructor dependency in MyConsumer, the AutoSubscriber would fail.

public class MyConsumer : IConsume<MessageA>, IConsume<MessageB>
{
    private readonly IDataStore _dataStore;

    public MyConsumer(IDataStore dataStore)
    {
        _dataStore = dataStore;
    }

    public void Consume(MessageA message) { }

    public void Consume(MessageB message) { }
}

To solve this, lets put the IoC-container or service locator in charge of resolving the consumers. Just replace the AutoSubscriber.CreateConsumer : Func<Type, object>

var subscriber = new AutoSubscriber(bus)
{
    CreateConsumer = t => objectResolver.Resolve(t)
};
subscriber.Subscribe(Assembly.GetExecutingAssembly());

Specify A Specific SubscriptionId

By default the AutoSubscriber will generate a unique SubscriptionId. If you would like it to be fixed, you can decorate the Consume method with the ConsumerAttribute. Why you would make it fixed, is something you can read up about here.

Lets say, the consumer above should have a fixed SubscriptionId for the consumer method of MessageB. Just decorated it and define a value for SubscriptionId.

[Consumer(SubscriptionId = "MyExplicitId")]
public void Consume(MessageB message) { }

Taking Control Of The SubscriptionId Generation

You could of course also take control of the actual SubscriptionId generation. Just replace the AutoSubscriber.GenerateSubscriptionId : Func<ConsumerInfo, string>.

var subscriber = new AutoSubscriber(bus)
{
    CreateConsumer = t => objectResolver.Resolve(t),
    GenerateSubscriptionId = c => AppDomain.CurrentDomain.FriendlyName + c.ConcreteType.Name
};
subscriber.Subscribe(Assembly.GetExecutingAssembly());

Note! Just a sample implementation. Ensure you have read and understood the importance of the SubscriptionId value.