DIContainer.md

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RockLib.Messaging with a DI/IOC container

RockLib.Messaging includes extension methods for registering with the Microsoft.Extensions.DependencyInjection container. There are three extension methods - AddSender, AddTransactionalSender, and AddReceiver - each with two variants. One variant registers the sender/receiver returned by a delegate and the other registers the sender/receiver from MessagingScenarioFactory by name.

It may not be necessary to call these methods directly - each implementation has its own set of extension methods. For example, SQS has AddSQSSender and AddSQSReceiver extension methods that end up calling AddSender and AddReceiver.

---

This example registers by delegate:

public void RegisterServices(IServiceCollection services)
{
    serivces.AddSender((IServiceProvider serviceProvider) =>
    {
        // TODO: retrieve any dependencies from serviceProvider
        ISender sender = // TODO: create ISender
        return sender;
    });

    serivces.AddTransactionalSender((IServiceProvider serviceProvider) =>
    {
        // TODO: retrieve any dependencies from serviceProvider
        ITransactionalSender sender = // TODO: create ITransactionalSender
        return sender;
    });

    serivces.AddReceiver((IServiceProvider serviceProvider) =>
    {
        // TODO: retrieve any dependencies from serviceProvider
        IReceiver receiver = // TODO: create IReceiver
        return receiver;
    });
}

---

This example registers with MessagingScenarioFactory:

public void RegisterServices(IServiceCollection services)
{
    // Registers ISender from MessagingScenarioFactory.CreateSender("MySender")
    serivces.AddSender("MySender");

    // Registers ITransactionalSender from MessagingScenarioFactory.CreateSender("MyTransactionalSender")
    // If the named sender is not an ITransactionalSender, a runtime error will occur.
    serivces.AddTransactionalSender("MyTransactionalSender");

    // Registers IReceiver from MessagingScenarioFactory.CreateReceiver("MyReceiver")
    serivces.AddReceiver("MyReceiver");
}

Dealing with multiple senders or receivers

In addition to registering the ISender, ITransactionalSender, or IReceiver interfaces, the extension methods also register a custom delegate - SenderLookup, TransactionalSenderLookup, or ReceiverLookup respectively. These custom delegates all have a single string parameter that takes the name of the sender/receiver to retrieve.

This example service is dependant on two instances of IReceiver and has a ReceiverLookup injected to retrieve them:

public class ExampleService
{
    private readonly IReceiver _dataReceiver;
    private readonly IReceiver _commandReceiver;

    public ExampleService(ReceiverLookup receiverLookup)
    {
        _dataReceiver = receiverLookup("DataReceiver");
        _commandReceiver = receiverLookup("CommandReceiver");
    }
}

Builder objects

The AddSender, AddTransactionalSender, and AddReceiver methods all return a builder interface - ISenderBuilder, ITransactionalSenderBuilder, and IReceiverBuilder - that have a Decorate method. These builders allow decorator implementations of ISender, ITransactionalSender, and IReceiver to be registered just as easily as the main implementations.

ForwardingReceiver is an example of a decorator implementation of IReceiver. And just like SQS, which has AddSQSSender and AddSQSReceiver extension methods, ForwardingReceiver has an AddForwardingReceiver extension method. Other decorator implementations should follow this example.