Wednesday, 15 November 2017

Enterprise Service Bus libraries for .NET – MassTransit

One in a series of posts giving a quick overview of ESB libraries for .NET

MassTransit is an open-source library which apparently began as a response to some perceived deficiencies in the version of NServiceBus that was around in 2007. The project did a major rewrite in 2014, introducing async support and switching from MSMQ to RabbitMQ as the preferred transport.

Messages

Messages are POCO classes. There is no requirement to inherit from any base class or implement a specific interface.

Publishing

http://masstransit-project.com/MassTransit/usage/producing-messages.html

Messages are published using IPublishEndpoint, which is provided by ConsumeContext for consumers or by the IBus interface

public async Task NotifyOrderSubmitted(IPublishEndpoint publishEndpoint)
{
    await publishEndpoint.Publish<OrderSubmitted>(new
    {
        OrderId = "27",
        OrderDate = DateTime.UtcNow,
    });
}

Subscribing

http://masstransit-project.com/MassTransit/usage/message-consumers.html

A subscribing class (or consumer) implements the IConsumer<T> interface.
public class UpdateCustomerConsumer :
    IConsumer<UpdateCustomerAddress>
{
    public async Task Consume(ConsumeContext<UpdateCustomerAddress> context)
    {
        await Console.Out.WriteLineAsync($"Updating customer: {context.Message.CustomerId}");

        // update the customer address
    }
}

A consumer needs to be connected to an endpoint to receive messages

var busControl = Bus.Factory.CreateUsingRabbitMq(cfg =>
{
    var host = cfg.Host(new Uri("rabbitmq://localhost/"), h =>
    {
        h.Username("guest");
        h.Password("guest");
    });

    cfg.ReceiveEndpoint(host, "customer_update_queue", e =>
    {
        e.Consumer<UpdateCustomerConsumer>();
    });
});

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