关于 scala：如何制作一个特征以与扩展 MappedLongForeignKey 的对象混合，该对象将覆盖 def asHtml 和 def validSelectValues？

How do I make a trait to mix in with an object that extends MappedLongForeignKey, that will override def asHtml and def validSelectValues?

我已将我的模型定义如下：

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

}
class Curr extends LongKeyedMapper[Curr] with IdPK with CreatedUpdated {
def getSingleton = Curr
object code extends MappedString(this, 100)
object name extends MappedString(this, 100)
}

object Country extends Country with LongKeyedMetaMapper[Country] with CRUDify[Long, Country] {
}
class Country extends LongKeyedMapper[Country] with IdPK with CreatedUpdated {
def getSingleton = Country
object name extends MappedString(this, 100)
object currid extends MappedLongForeignKey(this, Curr) {
override def asHtml = {
{Curr.find(By(Curr.id, this)).map(c => (c.name +"" + c.code)).openOr(Text(""))}
}
override def validSelectValues: Box[List[(Long, String)]] =
Full(Curr.findAll(OrderBy(Curr.name, Ascending)).map(c => (c.id.is, c.code.is)))
}
}

我将有许多这样的模型，我想删除为许多具有外键的模型定义 asHtml 和 validSelectValues 的冗余。我想我可以用一个特征 MyField 来做到这一点，它会混合到我的模型中，如下所示：

1	object currid extends {val MyModel = Curr } MappedLongForeignKey(this, Curr) with MyField[Curr] {

特征被定义为：

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trait MyField[T <: LongKeyedMetaMapper[T] with IdPK] {
val MyModel: T
override def asHtml = {
{MyModel.find(By(MyModel.id, this)).map(c => (c.name +"" + c.name)).openOr(Text(""))}
}
override def validSelectValues: Box[List[(Long, String)]] =
Full(MyModel.findAll(OrderBy(MyModel.name, Ascending)).map(c => (c.id.is, c.name.is)))
}

我的特质，如上所述，不起作用。这是编译器生成的错误：

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No implicit view available from net.liftweb.mapper.MyField[T] => Long.
[error] {MyModel.find(By(MyModel.id, this)).map(c => (c.name +"" + c.name)).openOr(Text(""))}
[error] ^
value name is not a member of type parameter T
[error] Full(MyModel.findAll(OrderBy(MyModel.name, Ascending)).map(c => (c.id.is, c.name.is)))
[error] ^

我将确保每个 MyModel 都有一个 name 成员。任何人都可以就如何实现这个特性提出建议吗？

谢谢！

相关讨论

我找到了解决办法。我创建了自己的 KeyedMapper、MetaMapper 和 MappedForeignKey。在示例中 MyData 和 MyForeignData 是两个数据库表，MyData 包含 MyForeignData 的外键。包含 CRUDify，您可以在浏览器中查看和编辑与表列一起显示的外键
覆盖 def primaryKeyDisplayField = table_column_field

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import scala.xml._
import net.liftweb.common._
import net.liftweb.mapper._
import net.liftweb.util._

trait MyMapper[OwnerType <: MyMapper[OwnerType]]
extends LongKeyedMapper[OwnerType] with IdPK {
self: OwnerType =>
}

trait MyMetaMapper[A <: MyMapper[A]]
extends LongKeyedMetaMapper[A]
with LongCRUDify[A] {
self: A =>
def primaryKeyDisplayField: BaseOwnedMappedField[A] = null
}

abstract class MyMappedForeignKey[T<:MyMapper[T], O<:MyMapper[O]](theOwner: T, _foreignMeta: => MyMetaMapper[O])
extends MappedLongForeignKey[T, O](theOwner, _foreignMeta) {
override def foreignMeta = _foreignMeta
override def dbIndexed_? = true
override def asHtml = {
{foreignMeta.findByKey(this.get)
.map(_.fieldByName(foreignMeta.primaryKeyDisplayField.name).openOr(Text("Error"))).openOr(Text("ERROR MyMappedForeignKey"))}
}
override def validSelectValues/*: Box[List[(Long, String)]]*/ = {
Full(foreignMeta.findAll(/*OrderBy(foreignMeta.primaryKeyField, Ascending)*/)
.map(i => (i.id.get,
i.fieldByName(foreignMeta.primaryKeyDisplayField.name).openOr(Text("ERROR")).toString())))
}
}

class MyData extends MyMapper[MyData] {
def getSingleton = MyData
object myForeignData extends MyMappedForeignKey(this, MyForeignData)
object name extends MappedString(this, 30)
}

object MyData extends MyData with MyMetaMapper[MyData] { }

class MyForeignData extends MyMapper[MyForeignData] {
def getSingleton = MyForeignData
object name extends MappedString(this, 30)
}

object MyForeignData extends MyForeignData with MyMetaMapper[MyForeignData] {
override def primaryKeyDisplayField = name
}