TraxBroadcast Attribute

The [TraxBroadcast] attribute opts a train into real-time GraphQL subscription events. Only trains decorated with this attribute will have their lifecycle transitions (onTrainStarted, onTrainCompleted, onTrainFailed, onTrainCancelled) published to WebSocket subscribers.

Trains without this attribute run normally but are silently skipped by both the local GraphQLSubscriptionHook and the remote GraphQLTrainEventHandler (used with UseBroadcaster()).

The attribute governs the user-facing subscription surface. If the host exposes the operations (admin) surface via ExposeOperationQueries()/ExposeOperationMutations(), it is treated as an observability host and streams every train regardless of this attribute. [TraxBroadcast] only matters on hosts that do not expose operations, where it picks the subset of trains that end users are allowed to watch.

Definition

[AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
public class TraxBroadcastAttribute : Attribute { }

A simple marker attribute with no properties, just opt-in/opt-out.

Example

[TraxQuery(Description = "Looks up a player profile")]
[TraxBroadcast]
[TraxAuthorize]
public class LookupPlayerTrain : ServiceTrain<LookupPlayerInput, LookupPlayerOutput>, ILookupPlayerTrain
{
    protected override Task<Either<Exception, LookupPlayerOutput>> Junctions() =>
        Chain<FetchPlayerJunction>().Resolve();
}

When LookupPlayerTrain completes, subscribers to onTrainCompleted that its posture admits receive a TrainLifecycleEvent with the train name, state, and timestamp.

Posture

A broadcast train streams its runs to subscribers, so it states who may receive them, the same way a train exposed as a query or mutation does. On an open endpoint it must carry [TraxAuthorize] (optionally with policies or roles) or [TraxAllowAnonymous], or the host does not start. Each event then reaches only the subscribers that posture admits. See Subscriptions.

Combined with TraxQuery / TraxMutation

[TraxBroadcast] and [TraxQuery]/[TraxMutation] are independent. You can use any combination:

Discovery

The [TraxBroadcast] metadata is available through ITrainDiscoveryService. Each TrainRegistration includes IsBroadcastEnabled. The trains GraphQL query also exposes this field.

Package

dotnet add package Trax.Effect

The attribute is defined in Trax.Effect so train classes can use it without depending on Trax.Api.GraphQL.