Sidio.Mediator

A simple implementation of the mediator pattern in .NET.

Core package (request abstractions)

Request validation package

Source generation for the Mediator service

Usage

Requests and requests handlers

// Define a request and request handler
public class MyRequest : IRequest<string>
{
    public string Name { get; init; }
}

public class MyRequestHandler : IRequestHandler<MyRequest, string>
{
    public Task<Result<string>> HandleAsync(MyRequest request, CancellationToken cancellationToken = default)
    {
        var result = Result<string>.Success($"Hello {request.Name}");
        // Or: Result<string>.Failure("error code", "error message");
        return Task.FromResult(result);
    }
}

// Provide an arbitrary type to register all request handlers in the assembly of the type:
services.AddMediatorRequestHandlers(typeof(MyRequest));

// Get the request handler from the service provider
var requestHander = serviceProvider.GetRequiredService<IRequestHandler<MyRequest, string>>();
var result = await requestHander.HandleAsync(new MyRequest { Name = "World" });

// or use dependency injection
public class MyClass
{
    public MyClass(IRequestHandler<MyRequest, string> requestHandler)
    {
    }
}

Http requests

// Define a request and request handler
public class MyHttpRequest : IHttpRequest<string>
{
    public string Name { get; init; }
}

public class MyHttpRequestHandler : IHttpRequestHandler<MyRequest, string>
{
    public Task<HttpResult<string>> HandleAsync(MyRequest request, CancellationToken cancellationToken = default)
    {
        var result = HttpResult<string>.Ok($"Hello {request.Name}");
        // Or for example: HttpResult<string>.Unauthorized();
        return Task.FromResult(result);
    }
}

Request validation

Request validation uses FluentValidation.

// Define a validator
public class MyRequestValidator : AbstractValidator<MyRequest>
{
    public MyRequestValidator()
    {
        RuleFor(x => x.Name).NotEmpty();
    }
}

// Provide an arbitrary type to register all validators in the assembly of the type:
services
    .AddMediatorRequestHandlers(typeof(MyRequest))
    .AddMediatorValidation(typeof(MyRequest));

Source generators (v2.0+)

In version 2.0 and later, Sidio.Mediator.SourceGenerator includes source generators that create an IMediator service implementation at compile time. This service works both with requests and request validation. The IMediator implementation contains a method for each request. For example, a request named MyRequest:

public class MyRequest : IRequest<string>;

The generated IMediator will have a method:

Task<Result<string>> MyRequestAsync(MyRequest request, CancellationToken cancellationToken = default);

Setup

• Add package reference to Sidio.Mediator.SourceGenerator in the project that contain the IRequest or IHttpRequest implementations.
• Register the IMediator service in your Startup.cs or Program.cs:

services
    .AddMediatorRequestHandlers(typeof(MyRequest)) // register the request handlers
    .AddMediatorValidation(typeof(MyRequest)) // register the request validators
    .AddMediatorService(); // register the IMediator service

Limitations

• Requests should have a unique name across the project which implements the source generator.
• Requests should not be nested in other classes.
• Requests should always implement IRequest, IRequest<T> or IHttpRequest<T>. Inheritance of base/abstract requests is not supported. Inheritance of request handlers should work.
• Types used in requests that are part of the parent namespace of that request should be included in global usings, e.g. in the csproj file:

<ItemGroup>
  <Using Include="MyNamespace" />
</ItemGroup>

• The IMediator service will be located in namespace Sidio.Mediator.