CQRS

CQRS stands for Command Query Responsibility Segregation. Greg Young has coined this term and most of the literature on the internet regarding CQRS would be associated with him.

In the simplest sense, consider the following scenario:

    UserService.scala
    trait UserService{
      def createUser(user: User): Unit
      def editUser(details: UserDetails): Unit
      def deleteUser(user:User): Unit
      def getUser(userId: Int): User
      def getUserFromName(name: String): User
      def getUserPreferences(userId:Int): UserPreference
    }

We have a UserService that declares calls to create/get/update users. Applying CQRS would result in splitting UserService into two separate services:

    trait UserReadService {
     def getUser(userId: Int): User
     def getUserFromName(name: String): User
     def getUserPreferences(userId: Int): UserPreference
    }

   trait UserWriteService...