Getting Started

Unit of work using the pipeline

Component: NServiceBus
NuGet Package: NServiceBus (8.x)


This sample leverages the pipeline provided unit of work management for message handlers. Using the pipeline abstraction is necessary when access to the incoming message and/or headers is required.

Code walk-through

Creating the Behavior

The behavior will wrap handler invocations and:

  1. Open a session to the database.
  2. Make the session available to the message handlers.
  3. Commit/Rollback the session depending on the outcome of the handler.
  4. Dispose the session.
class MyUowBehavior :
    MySessionProvider sessionProvider;

    public MyUowBehavior(MySessionProvider sessionProvider)
        this.sessionProvider = sessionProvider;

    public override async Task Invoke(IIncomingPhysicalMessageContext context, Func<Task> next)
        using (var session = await sessionProvider.Open())

                await next();

                await session.Commit();
            catch (Exception)
                await session.Rollback();


Note that the injected session factory is responsible for creating the session and that the session is registered in the pipeline context using context.Extensions.Set<IMySession>(session);. This will be used later to provide the session to the handlers.

Registering the behavior

The following code is needed to register the behavior in the receive pipeline.

var sessionProvider = new MySessionProvider();

var pipeline = endpointConfiguration.Pipeline;
pipeline.Register(new MyUowBehavior(sessionProvider), "Manages the session");

Providing the session to handlers

While it is possible to use the code contex.Extensions.Get<IMySession> in the handler, it is better to provide extension methods on IMessageHandlerContext to allow for a more terse syntax. In this sample the methods .Store<T> a .GetSession are provided:

static class MySessionContextExtensions
    public static IMySession GetSession(this IMessageHandlerContext context)
        return context.Extensions.Get<IMySession>();

    public static Task Store<T>(this IMessageHandlerContext context, T entity)
        return context.GetSession().Store(entity);

Message handlers

One of the benefits of a unit of work is that multiple handlers for the same message will share the same session and commit/rollback together. This is how the handlers look:

class MyMessageHandler1 :
    static ILog log = LogManager.GetLogger<MyMessageHandler1>();

    public async Task Handle(MyMessage message, IMessageHandlerContext context)
        await context.Store(new MyEntity());

        log.Info($"{context.MessageId} got UoW instance {context.GetSession().GetHashCode()}");

Running the sample

Run the sample. Once running, press any key to send messages. Note that for each given message the two message handlers will get the same session instance.

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