Immediate.Handlers 0.4.0

Immediate.Handlers

Immediate.Handlers is an implementation of the mediator pattern in .NET using source-generation. All pipeline behaviors are determined and the call-tree built at compile-time; meaning that all dependencies are enforced via compile-time safety checks. Behaviors and dependencies are obtained via DI at runtime based on compile-time determined dependencies.

Examples

• Minimal Api: Normal

Installing Immediate.Handlers

You can install Immediate.Handlers with NuGet:

Install-Package Immediate.Handlers

Or via the .NET Core command line interface:

dotnet add package Immediate.Handlers

Either commands, from Package Manager Console or .NET Core CLI, will download and install Immediate.Handlers.

Using Immediate.Handlers

Creating Handlers

Create a Handler by adding the following code:

[Handler]
public static class GetUsersQuery
{
    public record Query;

    private static ValueTask<IEnumerable<User>> HandleAsync(
        Query _,
        UsersService usersService,
        CancellationToken token)
    {
        return usersService.GetUsers();
    }
}

This will automatically create a new class, GetUsersQuery.Handler, which encapsulates the following:

• attaching any behaviors defined for all queries in the assembly
• using a class to receive any DI services, such as UsersService

Any consumer can now do the following:

public class Consumer(GetUsersQuery.Handler handler)
{
	public async Task Consumer(CancellationToken token)
	{
		var response = await handler.HandleAsync(new(), token);
		// do something with response
	}
}

In case your project layout does not allow direct for references between consumer and handler, the handler will also be registered as an IHandler<TRequest, Response>.

public class Consumer(IHandler<Query, IEnumerable<User>> handler)
{
	public async Task Consumer(CancellationToken token)
	{
		var response = await handler.HandleAsync(new(), token);
		// do something with response
	}
}

Creating Behaviors

Create a behavior by implementing the Immediate.Handlers.Shared.Behaviors<,> class, as so:

public sealed class LoggingBehavior<TRequest, TResponse>(ILogger<LoggingBehavior<TRequest, TResponse>> logger)
	: Behavior<TRequest, TResponse>
{
	public override async ValueTask<TResponse> HandleAsync(TRequest request, CancellationToken cancellationToken)
	{
		logger.LogInformation("LoggingBehavior.Enter");
		var response = await Next(request, cancellationToken);
		logger.LogInformation("LoggingBehavior.Exit");
		return response;
	}
}

This can be registered assembly-wide using:

[assembly: Behaviors(
	typeof(LoggingBehavior<,>)
)]

or on an individual handler using:

[Handler]
[Behavior(
	typeof(LoggingBehavior<,>)
)]
public static class GetUsersQuery
{
	// ..
}

Once added to the pipeline, the behavior will be called as part of the pipeline to handle a request.

Note: adding a [Behavior] attribute to a handler will disregard all assembly-wide behaviors for that handler, so any global behaviors necessary must be independently added to the handler override behaviors list.

Behavior Constraints

A constraint can be added to a behavior by using:

public sealed class LoggingBehavior<TRequest, TResponse>
	: Behavior<TRequest, TResponse>
	where TRequest : IRequestConstraint
	where TResponse : IResponseConstraint

When a pipeline is generated, all potential behaviors are evaluated against the request and response types, and if either type does not match a given constraint, the behavior is not added to the generated pipeline.

Registering with IServiceCollection

Immediate.Handlers supports Microsoft.Extensions.DependencyInjection.Abstractions directly.

Registering Handlers

services.AddHandlers();

This registers all classes in the assembly marked with [Handler].

Registering Behaviors

services.AddBehaviors();

This registers all behaviors referenced in any [Behaviors] attribute.

Performance Comparisons

All performance benchmarks reported use the following environment:

// * Summary *

BenchmarkDotNet v0.13.12, Windows 11 (10.0.22621.3007/22H2/2022Update/SunValley2)
12th Gen Intel Core i7-12700H, 1 CPU, 20 logical and 14 physical cores
.NET SDK 8.0.101
  [Host]     : .NET 8.0.1 (8.0.123.58001), X64 RyuJIT AVX2
  DefaultJob : .NET 8.0.1 (8.0.123.58001), X64 RyuJIT AVX2

Benchmarks.Simple

This benchmark tests the various mediator implementations with a single request/response handler.

Benchmarks.Large

This benchmark tests the various mediator implementations in the face of 999 request/response handlers.

Benchmarks.Behaviors

This benchmark tests a more realistic scenario of using 1 behavior and 1 service.