Event Forwarding

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As of Wolverine 2.2, you can use IEvent<T> as the message type in a handler as part of the event forwarding when you need to utilize Polecat metadata

WARNING

The Wolverine team recommends against combining this functionality with also using events as either a handler response or cascaded messages as the behavior can easily become confusing. Instead, prefer using custom types for handler responses or HTTP response bodies instead of the raw event types when using the event forwarding.

The "Event Forwarding" feature immediately pushes any event captured by Polecat through Wolverine's persistent outbox where there is a known subscriber (either a local message handler or a known subscriber rule to that event type). The "Event Forwarding" publishes the new events as soon as the containing transaction is successfully committed. This is different from the Event Subscriptions in that there is no ordering guarantee, and does require you to use the Wolverine transactional middleware for Polecat.

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The strong recommendation is to use either subscriptions or event forwarding, but not both in the same application.

To be clear, this will work for:

• Any event type where the Wolverine application has a message handler for either the event type itself, or IEvent<T> where T is the event type
• Any event type where there is a known message subscription for that event type or its wrapping IEvent<T> to an external transport

Timing wise, the "event forwarding" happens at the time of committing the transaction for the original message that spawned the new events, and the resulting event messages go out as cascading messages only after the original transaction succeeds -- just like any other outbox usage. There is no guarantee about ordering in this case.

To opt into this feature, chain the AddPolecat().EventForwardingToWolverine() call as shown below:

builder.Services.AddPolecat(opts =>
    {
        opts.Connection(connectionString);
    })
    .IntegrateWithWolverine()
    .EventForwardingToWolverine();

This does need to be paired with Wolverine configuration to add subscriptions to event types like so:

builder.Host.UseWolverine(opts =>
{
    opts.PublishMessage<ChartingFinished>()
        .ToLocalQueue("charting")
        .UseDurableInbox();

    opts.Policies.AutoApplyTransactions();
});