使用 Slick 3 进行动态排序答案

【问题标题】：Dynamic sortBy with Slick 3使用 Slick 3 进行动态排序
【发布时间】：2016-09-13 19:17:14
【问题描述】：

我正在尝试将 sortBy 动态包含到我的查询中，该查询根据查询参数中的字符串名称进行排序。在 Slick 3 中，这已被证明是相当棘手的。目前我的设置是：

trait Model {
    type ATable <: AbstractTable[_]

    def tableQuery: TableQuery[ATable]

    def sortMap: Map[String, Rep[_]]

    private def sortKey[T](e: ATable, sort: (String, SortOrder)): ColumnOrdered[_] = sort match {
       case (field, SortOrder.Asc) => ColumnOrdered(sortMap.getOrElse(field, throw new ClientException(s"Can't sort by $field")), Ordering(Ordering.Asc))
       case (field, SortOrder.Desc) => ColumnOrdered(sortMap.getOrElse(field, throw new ClientException(s"Can't sort by $field")), Ordering(Ordering.Desc))
    }
    def all(sort: (String, SortOrder)) = tableQuery.sortBy(sortKey(_, sort)).result
}

object User extends Model {
    type ATable = Tables.User
    val tableQuery = Tables.User

    val sortMap = Map( "id" -> tableQuery.id )
}

但是运行db.run(User.all(("id", SortOrder.Asc))会抛出以下错误：

slick.SlickException: No type for symbol name found in Vector[t2<@t3<UnassignedType>>]

有谁知道更好的解决方案或我哪里出错了？

【问题讨论】：

标签： scala orm slick-3.0

【解决方案1】：

我解决这个问题的方法是将我的sortMap 更改为包含具有隐式列类型的表类型（从Map[String, Rep[_]] 到Map[String, ATable => Rep[_]]）：

trait Model {
    type ATable <: AbstractTable[_]

    def tableQuery: TableQuery[ATable]

    def sortMap: Map[String, ATable => Rep[_]]

    private def sortKey(baseQ: Query[ATable, ATable#TableElementType, Seq], sort: (String, SortOrder)) = {
       val rep = sortMap.getOrElse(sort._1, throw new ClientException(s"Can't sort by ${sort._1}"))
       val orderedRep = sort._2 match {
          case SortOrder.Asc => (t: ATable) => ColumnOrdered(rep(t), slick.ast.Ordering(slick.ast.Ordering.Asc))
          case SortOrder.Desc => (t: ATable) => ColumnOrdered(rep(t), slick.ast.Ordering(slick.ast.Ordering.Desc))
       }
       q.sortBy(orderedRep)
   }

   def all(sort: (String, SortOrder)) = sortKey(tableQuery, sort).result
}

object User extends Model {
    type ATable = Tables.User
    val tableQuery = Tables.User

    val sortMap = Map( "id" -> { (t: ATable) => t.id } )
}

此解决方案的唯一次优方面是，如果将新列添加到数据库中，则必须手动将其添加到 sortKey。我正在考虑将这些地图包含在表格代码生成脚本中。

【讨论】：

【解决方案2】：

你只需要在生成中包含类似

的东西

val columns =  Map( "id" -> { (t: User) => t.id } )

并像这样使用它：

class UserDAO{ 
//...
baseQuery = filterContext.sort.foldLeft[Query[User, UserRow, Seq]](User) ((_, s) => UserColumnFilter.getSort(s,User.baseTableRow.columns));
//...
}

case class Sort(columnName:String,value: String) {}

case class FilterContext(filters:List[Filter],page:Int,pageSize:Int,sort:List[Sort])
    object UserColumnSort extends ColumnSort[User,UserRow](User)
    class ColumnSort[T<:Table[C],C](query:TableQuery[T]) 
    {      

      def getSort(s:Sort,columns:Map[String, T => Rep[_]]):Query[T, C, Seq] =  {
        val aux = columns.getOrElse(s.columnName, throw new Exception(s"Can't sort by ${s.columnName}"));
          val orderedRep = s.value match {
              case "asc" => (t: T) => ColumnOrdered(aux(t), slick.ast.Ordering(slick.ast.Ordering.Asc))
              case _ => (t: T) => ColumnOrdered(aux(t), slick.ast.Ordering(slick.ast.Ordering.Desc))
           }
           return query.sortBy(orderedRep);

      }
    }

【讨论】：