Question

我收到以下错误，但我不明白错误。

could not find implicit value for parameter tm: scala.slick.ast.TypedType[I] 
[error]   def id = column[I]("id",O.PrimaryKey) 
[error]                     ^

此错误指的是FkTable。我列出了代码，以及显示我意图的评论。我的计划是为表格打造一个很好的基础，然后我可以将我的CRUD服务关闭。

//ROWS
trait Row[I<:AnyVal,M[_]]{
  val id:M[I]
}
//TABLES
/**
 * @tparam I This is the type of the ID column in the table
 * @tparam M The row may contain a wrapper (such as Option) which communicates extra information to Slick for the row
 *           data.  M can be Id, which means that M[I] == Id[I] == I which means the Row item can contain a simple type.
 * @tparam R The class that represents a row of data.  As explained above, it is described by its __id__ which is of
 *           type M[I].
 */
abstract class BasicTable[I <:AnyVal,M[_], R <:Row[I,M]](tag: Tag, name: String) extends Table[R](tag, name) {
  def id: Column[I]
}

/**
 * @note The BasicTable takes Long,Option because longs can be incremented, and in slick this is communicated by an
 *       Option value of None. The None is read and tells Slick to generate the next id value.  This implies that the
 *       Row (R) must have a value __id__ that is an Option[Long], while the id column must remain Long.
 */
abstract class IncrTable[R <: Row[Long,Option]](tag: Tag, name: String) extends BasicTable[Long,Option,R](tag, name){
  def id = column[Long]("id", O.PrimaryKey, O.AutoInc)
}

/**
 *
 * @param refTable
 * @tparam I This is the type of the ID column in the table
 * @tparam R The class that represents a row of data.  As explained above, it is described by its __id__ which is of
 *           type M[I].
 * @tparam M2 The Wrapper for the referenced table's id value
 * @tparam R2 The class that represents the referenced table's row of data
 */
abstract class FkTable[I<: AnyVal,R<:Row[I,Id],M2[_], R2 <:Row[I,M2]](tag: Tag, name: String,refTable:TableQuery[BasicTable[I,M2,R2]]) extends BasicTable[I,Id,R](tag, name){
  def id = column[I]("id", O.PrimaryKey)

  //Foreign Key
  def fkPkconstraint = foreignKey("PK_FK", id, refTable)(_.id)
}

Answer 1

Slick的def column[T]在其签名中请求隐式TypedType[T]。光滑的TypedType用于Int，Double，Date等，但它找不到任何一种类型I。您可以在构造函数中向FkTable请求一个。只需将第二个参数列表添加到FkTable (implicit tt: TypedType[I])：

abstract class FkTable[...](...)(implicit tt: TypedType[I]) extends ...

这会将隐式查找移动到使用FkTable的位置，I可能设置为更具体的类型。然后，TypedType值会隐式传播到column[I]的调用。

光滑的通用创建错误

1 个答案: