Memoria

Publish notifications and messages on command success

Memoria can automatically publish in-process notifications and bus messages when a command handler succeeds. This is how you keep side effects (emails, search indexing, downstream services) decoupled from the command’s primary work.

This guide focuses on Azure Service Bus. The pattern is identical for RabbitMQ.

This guide assumes you have a messaging provider registered — see Configuration: Service Bus.

The shape

A command that opts in returns a CommandResponse carrying:

  1. Notifications — published in-process to every INotificationHandler<>.
  2. Messages — published to the configured bus (Service Bus, RabbitMQ, or any custom provider).
  3. Result value — the data returned to the caller.

Define the contracts

public record DoSomething(string Name) : ICommand<CommandResponse>;
public record SomethingHappened(string Name) : INotification;
public record SomethingToSendToServiceBus(string Name);

Implement the handlers

public class DoSomethingHandler : ICommandHandler<DoSomething, CommandResponse>
{
    public Task<Result<CommandResponse>> Handle(
        DoSomething command,
        CancellationToken cancellationToken = default)
    {
        var notification = new SomethingHappened(command.Name);
        var message = new SomethingToSendToServiceBus(command.Name);

        var response = new CommandResponse(
            notification,
            message,
            new { Message = $"Successfully processed command for: {command.Name}" });

        return Task.FromResult(Result.Ok(response));
    }
}

public class SomethingHappenedHandlerOne : INotificationHandler<SomethingHappened>
{
    public Task<Result> Handle(SomethingHappened notification, CancellationToken _ = default)
    {
        Console.WriteLine($"Handler One: {notification.Name}");
        return Task.FromResult(Result.Ok());
    }
}

public class SomethingHappenedHandlerTwo : INotificationHandler<SomethingHappened>
{
    public Task<Result> Handle(SomethingHappened notification, CancellationToken _ = default)
    {
        Console.WriteLine($"Handler Two: {notification.Name}");
        return Task.FromResult(Result.Ok());
    }
}

Dispatch

Use SendAndPublish instead of Send:

var result = await dispatcher.SendAndPublish(new DoSomething("MyName"));

The returned object contains the command’s result plus the result of every notification and message handler:

{
    "CommandResult": {
        "IsSuccess": true,
        "Value": { "Message": "Successfully processed command for: MyName" }
    },
    "NotificationResults": [
        { "IsSuccess": true },
        { "IsSuccess": true }
    ],
    "MessageResults": [
        { "IsSuccess": true }
    ]
}

What “on success” means

Notifications and messages are only published if the command handler returns a success result. A failure short-circuits — the original command failure is returned, no notifications fire, no messages reach the bus. This guarantees that downstream consumers never see a side effect for work that didn’t happen.

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