the user service

Before getting into the implementation of these service methods, let’s take a look at the user service API, found in UserService.scala. We find eight service methods here that mirror the eight user routes. Here is a shortened version with the three service methods we will look at in this tutorial:

package simbl.service

import scala.concurrent.Future
import simbl.api.UserInfo

/** service methods to back the [[UserRoute user routes]] */
trait UserService {

  /** creates and persists a new [[User]] from the [[UserInfo]], returning a
   * `UserInfo` reflecting the persisted `User`.
   *
   * @throws DuplicateUsernameException if a user with the supplied username
   * already exists
   * 
   * @throws DuplicateEmailException if a user with the supplied email already
   * exists
   */
  def createUser(info: UserInfo): Future[UserInfo]

  /** retrieves a [[User]] by username, returning a [[UserInfo]] reflecting the
   * persisted `User`. returns `None` if no such user by that username.
   */
  def retrieveUser(username: String): Future[Option[UserInfo]]

  /** updates a [[User]] by username, returning a [[UserInfo]] reflecting the
   * persisted `User`. returns `None` if no such user by that username.
   *
   * @throws DuplicateUsernameException if a user with the supplied username
   * already exists
   * 
   * @throws DuplicateEmailException if a user with the supplied email already
   * exists
   */
  def updateUser(username: String, info: UserInfo): Future[Option[UserInfo]]

}

The most important thing to note here is that each of the service methods is defined in terms of API classes UserInfo, and not in terms of the domain entities themselves. This is probably not necessary for such a simple application as this, but it’s a good practice, because the UI typically speaks in a slightly different language than the domain model. As a simple example, some user information, such as email or street address, should largely be considered private, and should be left out of most UI views.

As you can see, UserInfo is a simple case class that should convert in and out of JSON cleanly. It also contains a couple of methods for conversions between the API objects and the domain objects:

package simbl.api

import simbl.domain.Email
import simbl.domain.User
import simbl.domain.Username

case class UserInfo(
  username: String,
  email: String,
  fullname: String) {

  def toUser = User(Username(username), Email(email), fullname, None)

  /** updates a [[User]] according to the information in this [[UserInfo]] */
  def mapUser(user: User) = user.copy(
    username = Username(username),
    email = Email(email),
    fullname = fullname)

}

object UserInfo {

  def apply(user: User): UserInfo =
    UserInfo(user.username.username, user.email.email, user.fullname)

}

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A Persistence Framework for Scala and NoSQL

the user service