A Persistence Framework for Scala and NoSQL

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Here’s the code for UserServiceImpl.updateUser:

  def updateUser(username: String, info: UserInfo): Future[Option[UserInfo]] = {
      for {
        retrieved <- userRepo.retrieveOne(Username(username))
        modified = retrieved.map(info.mapUser)
        updated <- userRepo.update(modified)
      } yield {
    } recover {
      case e: DuplicateKeyValException[_] => handleDuplicateKeyVal(e, info)
      case e: NoSuchElementException => None

This method shows a variation on userRepo.retrieve: userRepo.retrieveOne. retrieveOne opens up the Option for you, throwing a NoSuchElementException if the Option is empty. We handle the NoSuchElementException in the recover clause, returning None if the User was not found. Akka HTTP will handle the None by returning a 404 Not Found, which is exactly what we want.

The retrieved in the for comprehension is a PState[User]. Calling retrieved.map produces another PState[User] that reflects the changes produced by the function passed to map. In this case, we call UserInfo.mapUser, which updates a User according to the information in the UserInfo. The resulting PState is stored in a local value named modified.

We then pass modified on to userRepo.update. This method persists the changes, but like userRepo.create, it might generate a DuplicateKeyValException if we try to update the user to have a conflicting username or email. Once again, we handle this problem in the recover clause, converting the longevity exception into a Simple Blogging service exception.

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