The MediatR Library
Clean Architecture is an Interface design. Everything is connected via Interfaces and their hidden Implementations. A request comes from the Framework layer to the Business handler via a Business interface. A request from the Business circle to the database or other services is also activated using an Adapter interface.
Mediator pattern and MediatR library are just another way to write Interfaces and
Implementations
(via the TRequest/TResponse type). In fact, you can simply define your own interface and
attach the corresponding implementation through your IOC container. However, the main reason I use
MediatR is because of its excellent dynamic pipeline behavior, which helps me separate most of the
cross-cutting concerns out of the main handler, makes everything cleaner and produces a concise,
testable handler class.
A very simple handler in MediatR looks like this
public class InsertUser
{
/// <summary>
/// Insert a new User and return that User
/// </summary>
public class Request : IRequest<Response>
{
public int ClientId { get; set; }
public string Username { get; set; }
public string Password { get; set; }
}
public class Response
{
public User User { get; set; }
}
public class Handler : IRequestHandler<Request, Response>
{
public async Task<Response> Handle(Request request, CancellationToken cancellationToken)
{
// implement your logic here
await CheckExistence(request.UserName);
// implement your logic here
var user = await SomeFunction(cancellationToken);
return new Response
{
User = user
}
}
}
}
In this simplest form, it doesn’t look so different from the way we usually do with a normal Interface. However, let’s imagine what will happen when you want to add these requirements
- Log the related information to debug later.
- Track the process metrics to monitor and analyze performance.
- Lock the process to avoid race-condition.
- Transform the request/response format in a pre-defined way.
- Handle errors.
- Other cross-cutting concerns?…
- A more important question: How to group related requests and re-use these cross-cutting concern handlers?
