Cogito.MassTransit.DependencyInjection 3.1.0

Cogito.MassTransit.DependencyInjection

Registers MassTransit consumers, sagas and activities from attributes on the types themselves, onto any bus.

Why

AddMassTransit wants every consumer and saga listed inside its configuration lambda, so the place a bus is set up has to know every type that runs on it. With attributes, each type says which bus it runs on and how its endpoint is named, and a host only adds the assemblies it wants. The types are registered through MassTransit's own registration API, so they behave exactly as if they had been added in the lambda.

Install

dotnet add package Cogito.MassTransit.DependencyInjection

Use

Apply the attributes:

[AddConsumer(EndpointName = "orders")]
public class SubmitOrderConsumer : IConsumer<SubmitOrder> { ... }

[AddSagaStateMachine(EndpointName = "order-state")]
[InMemorySagaRepository]
public class OrderStateMachine : MassTransitStateMachine<OrderState> { ... }

Then add the bus, and the assemblies whose types to register, with AddFromAttributes from Cogito.DependencyInjection:

services.AddMassTransit(x => x.UsingRabbitMq((context, cfg) => cfg.ConfigureEndpoints(context)));
services.AddFromAttributes(typeof(Program).Assembly);

The types join the endpoints ConfigureEndpoints creates. It does not matter whether AddFromAttributes comes before or after AddMassTransit, except for sagas without a repository attribute (below).

The registrations are made on the IServiceCollection, so an Autofac host that populates from it gets them too.

Attributes

Each takes:

• Bus, the bus to register onto. It is IBus unless set to the interface given to AddMassTransit<TBus>. Apply the attribute more than once to register a type onto more than one bus.
• Definition, a MassTransit definition for the type, such as a ConsumerDefinition<T>.
• ExcludeFromConfigureEndpoints, which leaves the type off the endpoints ConfigureEndpoints creates.

All but [AddActivity] also take the endpoint's EndpointName, PrefetchCount, ConcurrentMessageLimit, IsTemporary, InstanceId and ConfigureConsumeTopology. [AddActivity] takes ExecuteEndpointName and CompensateEndpointName; configure anything more about its endpoints with a definition. Endpoint properties that are not set fall to the definition, or to the bus's endpoint name formatter.

public interface IBackOfficeBus : IBus { }

[AddConsumer(Bus = typeof(IBackOfficeBus), EndpointName = "reports", ConcurrentMessageLimit = 4)]
public class ReportConsumer : IConsumer<RunReport> { ... }

Saga repositories

A saga needs a repository. Apply a repository attribute to the saga, or to its state machine:

• [InMemorySagaRepository] keeps instances in memory.
• [EntityFrameworkSagaRepository], from Cogito.MassTransit.EntityFrameworkCore.DependencyInjection, keeps them in Entity Framework Core.

Without one, the saga takes the repository provider set on the bus, such as SetInMemorySagaRepositoryProvider(), but only if AddFromAttributes comes before AddMassTransit: MassTransit assigns the provider's repositories as AddMassTransit completes. A saga registered from attributes that has no repository fails the host's startup, rather than its first message.

License

MIT.