Call AddConsumer using generic type - asp.net-core

Question

I have a problem when I am using MassTransit v5.1.5 with the default ASP.NET Core DI. I have the following code:
var consumers = typeof(CompanyApplicationService).Assembly
.GetTypes()
.Where(t => typeof(IConsumer).IsAssignableFrom(t))
.ToList();
consumers.ForEach(
c => services.AddSingleton(typeof(IConsumer), c));
cqrsConfig.ServiceCollectionConfig = (x) =>
{
consumers.ForEach(consumer => x.AddConsumer<consumer>());
};
So I have a separate assembly where my implementations of IConsumer<T> are. I have those consumers loaded into a list, but when I try to add them using the MassTransit.ExtensionsDependencyInjectionIntegration.IServiceCollectionConfigurator.AddConsumer<T>() method I cannot pass the type that I have previously loaded. So any ideas on this?
I have tried to register the consumers like:
cqrsConfig.InMemoryBusConfig = (c) =>
{
var host = c.Host;
c.ReceiveEndpoint(busName, ep =>
{
ep.LoadFrom(services.BuildServiceProvider());
});
};
but that also doesn't work for me.

Answer 1

There's more than one thing that is wrong here.
In order to know, which message to handle, MassTransit needs to know the generic interface type of the consumer. You, however, register all consumers as IConsumer, which is apparently wrong.
Consumers are by definition isolated to the message scope. So, consumers are instantiated and disposed for each message, and, therefore, cannot be singletons.
You need to register your consumers like it is described in the documentation:
services.AddScoped<OrderConsumer>();
or
services.AddMassTransit(x =>
{
x.AddConsumer<OrderConsumer>();
});
When consumers are added to the service collection, you also need to register the bus as it is shown in the documentation, so you use the service provider delegate:
services.AddSingleton(provider => Bus.Factory.CreateUsingRabbitMq(cfg =>
{
var host = cfg.Host("localhost", "/", h => { });
cfg.ReceiveEndpoint(host, "submit-order", e =>
{
e.LoadFrom(provider);
});
}));
services.AddSingleton<IBus>(provider => provider.GetRequiredService<IBusControl>());