Using complex type messages with EasyNetQ

This is the second post in series about EasyNetQ. In the first post I am explaining how to install RabbitMQ and write simple application which publishes and consumes string messages.

Complex type message

Usually you will need to send more complex types than string. Fortunately it is no harder than sending string messages. All you need to do is to create library project which will contain your message types and share it between publishers and consumers.

Load the example application you made in the first post and add new Class Library project to the solution named Messages. Add new class PersonName to that project which will represent persons name:

Next, add new class CreateAccountMessage to represent a message which is raised when user created new account:

Consuming complex type messages

There really is no difference in consuming complex type message from simple type message. All dirty work related to routing, serialisation and deserialisation is handled by EasyNetQ. All you have to do is to add reference to Messages project from your ConsumerApplication project and change Subscribe registration to

bus.Subscribe<CreateAccountMessage>("consumer1", message =>
    Console.WriteLine("Creating account for {0} {1}, age {2}.", message.Name.FirstName, message.Name.LastName, message.Age)
);

Publishing complex type messages

Again, as you would expect, nothing complicated here. Just add reference to Messages project from the PublisherApplication and change the call to Publish method to:

bus.Publish(new CreateAccountMessage("Joe", "Smith", 26));

Now run the ConsumerApplication by right clicking project name in Solution Explorer and selecting Debug > Start new instance. Next run the PublishedApplication project in the same way and you should see ConsumerApplication receiving the message.

Why do I have to share Messages

As you could see there is a need for sharing project with messages between publisher and consumer project. This is dictated by the way EasyNetQ is handling message delivery. Under the hood, the EasyNetQ is registering exchange and queue in RabbitMQ server using message strongly type names, which in our case will be Messages.CreateAccountMessage:Messages. If the consumer will subscribe to the bus with message type residing in different assembly (such as ConsumerApplication) then it won’t match the type of published message, even though they have the same definition.
Anyway, the requirement for sharing message types is not that bad as it will prevent problems with different versions of messages being published and consumed. It also allows for sharing message’s behaviour, as only data is carried over the message bus.

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