在Slick中使用自定义列类型时进行过滤

Question

使用自定义列类型时,我在Slick 2.1.0中查询/过滤时遇到一些困难.我的问题的简化版本:

import scala.slick.driver.MySQLDriver.simple._

sealed class Status(val intValue: Int)
case object Active extends Status(1)
case object Disabled extends Status(2)
case object Deleted extends Status(3)

case class TableMapping(id: Long, status: Status)

class MyTableDefinition(tag: Tag) extends Table[TableMapping](tag, "sometable") {
  implicit val statusColumnType = MappedColumnType.base[Status, Int](statusToInt, intToStatus)

  def id = column[Long]("ID", O.PrimaryKey, O.AutoInc)
  def status = column[Status]("STATUS", O.NotNull, O.Default(Active))
  def * = (id, status) <> (TableMapping.tupled, TableMapping.unapply)

  private def statusToInt(s: Status): Int = s.intValue
  private def intToStatus(i: Int): Status = i match {
    case 1 => Active
    case 2 => Disabled
    case _ => Deleted
  }
}

class MyTableDao {
    val Items = TableQuery[MyTableDefinition]
    def byId(id: Long)(implicit session: Session): Option[TableMapping] = {
      Items.filter(_.status =!= Deleted).firstOption
    }
}

我得到一个编译错误:

Items.filter(_.status =!= Deleted).firstOption

错误说明:

value =!= is not a member of scala.slick.lifted.Column[Status]
[error] def byId(id: Long)(implicit session: Session): Option[TableMapping] =
  Items.filter(_.status =!= Deleted).firstOption

我做错了什么想法？也许有一种更好的方法可以做到这一点,我不知道？

Answer 1

问题是Scala编译器将寻找隐式转换Deleted.type而不是Status.

正如Deleted声明object它不是一个类,它的实际类是Deleted.type,所以你只需要帮助编译器理解它实际上是一个Status.怎么样？你可以试试

class MyTableDao {
val Items = TableQuery[MyTableDefinition]

def byId(id: Long)(implicit session: Session): Option[TableMapping] =
    Items.filter(_.status =!= Deleted.asInstanceOf[Status]).firstOption
}

那就行了.

让我知道如果它确实有效,我面临着类似的问题,我能够摆脱它做到这一点.

Answer 2

您的自定义类型映射器需要在 DAO 范围内；我会做类似的事情：

trait MyTypeMapper {
  protected implicit val statusColumnType = 
    MappedColumnType.base[Status, Int](_.intValue, intToStatus)

  private def intToStatus(i: Int): Status = i match {
    case 1 => Active
    case 2 => Disabled
    case _ => Deleted
  }
}

然后将特征混合到你的表映射器和 dao 中：

class MyTableDefinition(tag: Tag) 
  extends Table[TableMapping](tag, "sometable")
  with MyTypeMapper {...}

class MyTableDao extends MyTypeMapper{...}