Message

Overview

Message is the base class every ServiceConnect message inherits from. It carries a single piece of state — the correlation id used to relate messages across a conversation: a request and its reply, a command and the events it produces, and every message emitted by one process-manager instance. You reach for it whenever you define a new message contract.

See Messages for the conceptual tour.

Reference

`Message(Guid correlationId)`

public class Message(Guid correlationId)

Primary constructor. Every derived message type passes a correlation id up to this base constructor; derived types typically expose their own primary constructor that forwards it.

Parameters

correlationId — the correlation id to attach to the message. Pass a fresh Guid.NewGuid() when starting a new conversation, or forward the id of an inbound message when continuing one.

Remarks. The constructor is the primary way to supply the correlation id. The property also has an init accessor so deserialisers and object-initializer expressions can populate it — see remarks under CorrelationId below.

`CorrelationId`

public Guid CorrelationId { get; init; }

Gets the correlation id used to relate this message to a broader conversation.

Remarks. The init accessor allows object-initializer syntax and deserialisers to populate the property, but prevents post-construction reassignment in ordinary code. Pass the id through the primary constructor in production code; the init accessor is there for deserialisers and test helpers that construct messages via object initializers rather than constructors.

Usage

Defining a message type

public sealed record OrderPlaced(Guid correlationId, Guid OrderId, decimal Total)
    : Message(correlationId);

A message type inherits Message and forwards a correlation id through its own primary constructor. Using sealed record gives value equality and a compact declaration; the correlation id flows into the base class verbatim.

Propagating correlation id from an inbound message

public sealed class PlaceOrderHandler : IMessageHandler<PlaceOrder>
{
    public async Task HandleAsync(PlaceOrder message, IConsumeContext context, CancellationToken cancellationToken = default)
    {
        // ... persist the order ...

        await context.Bus.PublishAsync(new OrderPlaced(
            correlationId: message.CorrelationId,
            OrderId: message.OrderId,
            Total: message.Total));
    }
}

When a handler emits a follow-up event, it forwards the inbound message’s correlation id into the new message so downstream subscribers and log aggregators can stitch the full conversation together. Generating a fresh id here would break the trace. context is passed directly to HandleAsync — reach for it when you need the bus, the reply helper, or other per-message metadata.