Question

在Scala Lift框架中，如何创建一个可以混合到映射字段中的特性，而不必为数据库中的许多字段覆盖相同的属性？

我想在下面的代码中消除一些冗余。具体来说，我不想重复添加：

override def writePermission_? = false
override def readPermission_? = false
override def shouldDisplay_? = false
override def show_? = false
override def dbDisplay_? = false

表示几个db字段。我认为，解决这个问题的方法是写一个看起来像这样的特征：

trait PrivateField extends ...??? {
    override def writePermission_? = false
    override def readPermission_? = false
    override def shouldDisplay_? = false
    override def show_? = false
    override def dbDisplay_? = false
}

然后将其混合到对象覆盖中，如下所示：

object owner extends MappedLongForeignKey(this, User) with PrivateField
object status extends MappedInt(this) with PrivateField

等。这是解决问题的好方法吗？如果是的话，有关如何编写特征的任何建议吗？下面是我想减少冗余的代码。

class Mytable extends LongKeyedMapper[Mytable] with IdPK {

  def getSingleton = Myclass

  object owner extends MappedLongForeignKey(this, User) {
    override def writePermission_? = false
    override def readPermission_? = false
    override def shouldDisplay_? = false
    override def show_? = false
    override def dbDisplay_? = false
  }
  object description extends MappedString(this, 140)
  object name extends MappedString(this, 140)
  object status extends MappedInt(this) {
    override def writePermission_? = false
    override def readPermission_? = false
    override def shouldDisplay_? = false
    override def show_? = false
    override def dbDisplay_? = false
  }
  object entry_number extends MappedInt(this) {
    override def writePermission_? = false
    override def readPermission_? = false
    override def shouldDisplay_? = false
    override def show_? = false
  }
  object quanitity extends MappedDecimal(this, MathContext.DECIMAL64, 2) {
    override def writePermission_? = false
    override def readPermission_? = false
    override def shouldDisplay_? = false
    override def show_? = false
    override def dbDisplay_? = false
  }
}

object Mytable extends Mytable with LongKeyedMetaMapper[Mytable] with CRUDify[Long, Mytable] {

  override def editMenuLoc:Box[Menu] = Empty
  override def deleteMenuLoc:Box[Menu] = Empty
  override def viewMenuLoc:Box[Menu] = Empty
  override def createMenuLocParams: List[Loc.AnyLocParam] = List(If(User.loggedIn_? _, "Not logged in"))
  override def showAllMenuLocParams: List[Loc.AnyLocParam] = List(If(User.loggedIn_? _, "Not logged in"))

  override def findForList(start: Long, cnt: Int): List[Mytable] =
    findAll(StartAt(start), MaxRows(cnt), By(owner, User.currentUser))

  override def findForParam(in: String): Box[Mytable] =
    for {
      user <- User.currentUser
      id <- Helpers.asLong(in)
      mytable <- find(By(this.id, id), By(owner, user))
    } yield mytable
}

谢谢，

Answer 1

最简单的方法可能是使用self type annotation：

trait PrivateField[FieldType <: Any, OwnerType <: Mapper[OwnerType]] {
  self: MappedField[FieldType, OwnerType] =>
  override def writePermission_? = false
  override def readPermission_? = false
  override def shouldDisplay_? = false
  override def show_? = false
}

然后你可以这样使用它：

MappedInt(this) with PrivateField[Int, Mytable]

如何制作一个可以混合到映射字段中的特性，以便我不必为数据库中的许多字段覆盖相同的属性？

1 个答案: