Relationships

Info

Normal Relationship handling is the use of embedded documents. However, sometimes there is a need for relationsips beetween collections. There is a Relations Trait to be used in case classes for easy relationship handling.

Relations trait

The Relations trait extends DAO case classes with relationship functions.

• relatedRecordForOneToOne (OneToOneRelationship and reference value needed)
• relatedRecordsForOneToMany (OneToManyRelationship and reference value needed)

Demo

Simple Setup.

• User Collection(should have one login and multiple friends)
• Login Collection
• Friend Collection

  case class User(id: Long, name: String, loginId: String)
  case class Login(id: String, email: String, password: String)
  case class Friend(id: Long, name: String, userId: Long)
  
  object UserDAO extends MongoDAO[User](database, "user")
  object LoginDAO extends MongoDAO[Login](database, "login")
  object FriendDAO extends MongoDAO[Friend](database, "friend")

For relationship setup we create two Relationships in the UserDAO.

• OneToOne loginRelation (LoginDAO, key is id in user collection)
• OneToMany friendsRelation (FriendDAO, key is userId in friend collection)

object UserDAO extends MongoDAO[User](provider, "user") {
  lazy val loginRelation   = OneToOneRelationship(LoginDAO, "id")
  lazy val friendsRelation = OneToManyRelationship(SimplePersonDAO, "userId")
}

We extend the User case class with the Relations trait and add relation specific functions.

• login (create an Option of Login)
• friends (create a List of Friend)

case class User(id: Long, name: String, loginId: String) extends Relations {

  def login: Option[Login] = relatedRecordForOneToOne(UserDAO.loginRelation, loginId)

  def friends: List[SimplePerson] = relatedRecordForOneToMany(UserDAO.friendsRelation, id)

}