Introducing models

A model is a domain object, which maps to database entities. For example, a social networking application has users. The users can register, update their profile, add friends, post links, and so on. Here, the user is a domain object and each user will have corresponding entries in the database. Therefore, we could define a user model in the following way:

case class User(id: Long,
                loginId: String,
                name: Option[String],
                dob: Option[Long])
object User { def register (loginId: String,...) = {…}
...
}

Earlier, we defined a model without using a database:

case class Task(id: Int, name: String)

object Task {

  private var taskList: List[Task] = List()

  def all: List[Task] = {
    taskList
  }

  def add(taskName: String) = {
    val lastId: Int = if (!taskList.isEmpty) taskList.last.id else 0
    taskList = taskList ++ List(Task(lastId + 1, taskName))
  }

  def delete(taskId: Int) = {
    taskList = taskList.filterNot(task =...