Cannot use more than one gateway transformation

[alex91352]

The method GatewayRegistrations.AddGateway<TSubscription, TSubscriptionOptions, TProducer, TProduceOptions, TTransform> registers a GatewayHandler in the SubscriptionBuilder.

Since AddGateway passes the GatewayHandler to AddEventHandler as an IEventHandler, and AddEventHandler tries to register the handler in the service collection as a singleton, this means that only the first GatewayHandler is registered in the service collection. As a result, the first GatewayHandler (and its transformation) is used for all gateway subscriptions.

eventuous/src/Gateway/src/Eventuous.Gateway/Registrations/GatewayRegistrations.cs

Lines 127 to 157 in ed2c62e

	public static IServiceCollection AddGateway<TSubscription, TSubscriptionOptions, TProducer, TProduceOptions, TTransform>(
	this IServiceCollection services,
	string subscriptionId,
	Action<TSubscriptionOptions>? configureSubscription = null,
	Action<SubscriptionBuilder<TSubscription, TSubscriptionOptions>>? configureBuilder = null,
	bool awaitProduce = true
	)
	where TSubscription : EventSubscription<TSubscriptionOptions>
	where TProducer : class, IEventProducer<TProduceOptions>
	where TProduceOptions : class
	where TTransform : class, IGatewayTransform<TProduceOptions>
	where TSubscriptionOptions : SubscriptionOptions {
	services.TryAddSingleton<TTransform>();
	services.AddSubscription<TSubscription, TSubscriptionOptions>(
	subscriptionId,
	builder => {
	builder.Configure(configureSubscription);
	configureBuilder?.Invoke(builder);
	builder.AddEventHandler(GetHandler);
	}
	);
	return services;
	IEventHandler GetHandler(IServiceProvider sp) {
	var transform = sp.GetRequiredService<TTransform>();
	var producer = sp.GetRequiredService<TProducer>();
	return new GatewayHandler<TProduceOptions>(new GatewayProducer<TProduceOptions>(producer), transform.RouteAndTransform, awaitProduce);
	}
	}

eventuous/src/Core/src/Eventuous.Subscriptions/Registrations/SubscriptionBuilder.cs

Lines 47 to 53 in ed2c62e

	public SubscriptionBuilder AddEventHandler<THandler>(Func<IServiceProvider, THandler> getHandler)
	where THandler : class, IEventHandler {
	Services.TryAddSingleton(getHandler);
	AddHandlerResolve(sp => sp.GetRequiredService<THandler>());
	return this;
	}

For example, if I register two gateway subscriptions:

services.AddGateway<StreamSubscription, StreamSubscriptionOptions, EventStoreProducer, EventStoreProduceOptions, SellOrderTransformation>("SellOrders", ...);
services.AddGateway<StreamSubscription, StreamSubscriptionOptions, EventStoreProducer, EventStoreProduceOptions, BuyOrderTransformation>("BuyOrders", ...);

then both subscriptions will use SellOrderTransformation.

[alexeyzimarev]

Yeah, that can actually be fixed the same way as event handlers and checkpoint stores are attached to subscriptions. The problem is that gateways DI integration is way less comprehensive than DI stuff for subs as it took me weeks to figure things out there. It definitely worth spending time and figure better DI support for gateways as well.

[gius]

Hi, any update on this? How do you use multiple gateways? Or do you use just a single gateway for all cases?

A quick workaround we use is to create a custom sub class of TProduceOptions per subscription.