Question

我有一个像这样的伴侣对象：

object Addresses extends Table[Address]("address"){
  //some mapping columns
  .... 

  //a method I want to made generic 
  def findAll(limit: Option[Int], offset: Option[Int]): Seq[Address] = DBTest.db.withSession { implicit db: Session =>
    (limit, offset) match {
      case (Some(l), Some(o)) => Addresses.map { a => a }.drop(o).take(l).list
      case (None, None) => Addresses.map { a => a }.drop(ConfigurationsLoader.DefaultOffset).take(ConfigurationsLoader.DefaultLimit).list
      case (Some(l), None) => Addresses.map { a => a }.take(l).list
      case (None, Some(o)) => Addresses.map { a => a }.drop(o).list
    }
  }

案例类Address的

。

因为我有很多这样的对象（每个都定义一个表）我想在一个特性中移动findAll方法使它成为通用的，我试着这样做：

trait DbGenericOperations[T, U <: Table[T]]{
  val entities: U
  /**
   * Based on REST conventions, for listing it's good to use limit and offset, like: /entities?limit=25&offset=50.
   */
  def findAll(limit: Option[Int], offset: Option[Int]): Seq[T] = DBTest.db.withSession { implicit db: Session =>
    (limit, offset) match {
      case (Some(l), Some(o)) => entities.map { a => a }.drop(o).take(l).list
      case (None, None) => entities.map { a => a }.drop(ConfigurationsLoader.DefaultOffset).take(ConfigurationsLoader.DefaultLimit).list
      case (Some(l), None) => entities.map { a => a }.take(l).list
      case (None, Some(o)) => entities.map { a => a }.drop(o).list
    }
  }
}

正如您所注意到的，entities基本上是我的伴侣对象。

现在的问题是我不能像这样重写我的对象定义：

object Addresses extends Table[Address]("address") with DbGenericOperations[Address, Addresses]{

因为它说Addresses不是类型......

我对scala很新，我想知道：有什么方法可以解决这个问题吗？

更新：我这样做了：

trait DbGenericOperations[T]{
      /**
       * Based on REST conventions, for listing it's good to use limit and offset, like: /entities?limit=25&offset=50.
       */
      def findAll(limit: Option[Int], offset: Option[Int], entities: Table[T]): Seq[T] = DBTest.db.withSession { implicit db: Session =>
        (limit, offset) match {
          case (Some(l), Some(o)) => entities.map { a => a }.drop(o).take(l).list
          case (None, None) => entities.map { a => a }.drop(ConfigurationsLoader.DefaultOffset).take(ConfigurationsLoader.DefaultLimit).list
          case (Some(l), None) => entities.map { a => a }.take(l).list
          case (None, Some(o)) => entities.map { a => a }.drop(o).list
        }
      }
    }

并声明这样的伴侣对象： object Addresses extends Table[Address]("address") with DbGenericOperations[Address]

但我不喜欢使用这种方法：

val results = Addresses.findAll(limit, offset, Addresses)

如果有更好的解决方案，请告诉我......

Answer 1

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Scala泛型问题

1 个答案: