Greyhound

Greyhound is our own implementation of a generic Mediator pattern. Essentially, it allows us to decouple the business logic by defining Requests, Responses, Handlers, and Notifications.

The Basics

With Greyhound, you issue requests and commands to get a response from a handler. You don’t care where the handler is, just that it processes your Request or Command and gives you a Response.

Requests and Commands

Requests and Commands are messages that ask for something to be done or tell the system to do something. They are the input to the system.

A Request is a message that asks for something to be returned. A Command is a message that tells the system to do something. A request is analogous to the “GET” method in HTTP/REST, and a command is analogous to “POST”, “PUT”, or “DELETE” in HTTP/REST.

The real technical difference is the type of response that is returned. A Request will return a Response<T> where T is the expected result type. A Command will return a non-generic Response.

Responses

A Response is the result of a request or command. You should always check the IsSuccess property when you get back a Response. If this property is false, then the Error property will have details of the error.

Request and Command Handlers

Handlers are the classes that do the actual work of processing a request or command and returning a Response<T> or Response, respectively.

Notifications

Notifications are hooks raised by the system indicating that something has happened.