/MediatorSamples

Primary LanguageC#

Clean architecture with ASP.NET Core

This sample shows a more complete example on how Mediator can be used, following an onion/clean architecture style.

Run

Run the application in Visual Studio or through the dotnet CLI. The Swagger UI should be visible at http://localhost:5000/swagger/index.html.

REST client

Use the post-todo.http file and the "REST Client" VSCode extension to test it out:

POST http://localhost:5000/api/todos HTTP/1.1
content-type: application/json

{
  "title": "",
  "text": "This is a todo without a title, we should get an error..."
}

HTTP/1.1 400 Bad Request
Connection: close
Date: Mon, 17 May 2021 10:51:45 GMT
Content-Type: application/json; charset=utf-8
Server: Kestrel
Transfer-Encoding: chunked

{
  "errors": [
    "'Title' must be between 1 and 40 characters. You entered 0 characters."
  ]
}

Code smells

Exceptions for control flow

Exceptions are not good for control flow, but in this sample a ValidationException is used to "return early" from a generic pipeline behaviour. The MessageValidatorBehaviour will process any message sent through mediator which implements IValidate.

Ideally, the return value for the AddTodoItem was some sort of Result<TResponse, ValidationError> or OneOf<TResponse, ValidationError> type, in which case we could just return an instance of ValidationError in the pipeline behaviour before invoking the handler. Then the caller would have to handle both success and failure cases, TResponse or ValidationError and return statuscode accordingly.