如何將TableQuery作爲泛型傳遞，然後使用它？

Question

我想模板出一個TableQuery成員，但路徑依賴類型搞砸了我。我有一個典型的代碼生成的表像這樣：

trait TablesContainer { 
    case class MembersRow(firstName:String, lastName:String) 

    class Members(_tableTag: Tag) extends Table[MembersRow](_tableTag, Some("dbo"), "MEMBERS") { 
     def * = (firstName, lastName) <> (MembersRow.tupled, MembersRow.unapply) 

     val firstName: Rep[String] = column[String]("FIRM_NAME") 
     val lastName: Rep[String] = column[String]("LAST_NAME") 
    } 
} 

然後我試圖創建一個類，將採取TableQuery（在典型的多DB模式），像這樣：

class TemplateHolder(profile: RelationalProfile) { 
    import profile.api._ 

    class InsertionTemplate[T <: Table[E], E](tableQuery: TableQuery[T]) { 
     def apply(insertRow:E) = { 
      tableQuery += insertRow 
     } 
    } 
} 

然後我想使用它，像這樣：

def template = new InsertionTemplate(TableQuery[TablesContainer.Members]) 

template.apply(MembersRow("Joe", "Bloggs")) 

只有我得到的錯誤：

Error:(134, 28) inferred type arguments [com.test.TablesContainer.Members,Nothing] do not conform to class InsertionTemplate's type parameter bounds [T <: RelationalProfileConstants.this.profile.api.Table[E],E] 
    def template = new InsertionTemplate(TableQuery[TablesContainer.Members]) 

然後這一個：

Error:(134, 60) type mismatch; 
found : slick.lifted.TableQuery[com.test.TablesContainer.Members] 
required: RelationalProfileConstants.this.profile.api.TableQuery[T] 
    (which expands to) slick.lifted.TableQuery[T] 
    def template = new InsertionTemplate(TableQuery[TablesContainer.Members]) 

我在做什麼錯？

Answer 1

下面的代碼編譯沒有問題。 InsertionTemplate方法無法推斷E的類型，所以明確提供類型參數解決了問題。您的導入範圍也可能存在潛在問題。請確保您有如下所示的進口說明import driver.api._。

trait Container1 { 

    self: HasDatabaseConfigProvider[JdbcProfile] => 

    import driver.api._ 

    trait TablesContainer { 
     case class MembersRow(firstName:String, lastName:String) 
     class Members(_tableTag: Tag) extends Table[MembersRow](_tableTag, Some("dbo"), "MEMBERS") { 
     def * = (firstName, lastName) <> (MembersRow.tupled, MembersRow.unapply) 
     val firstName: Rep[String] = column[String]("FIRM_NAME") 
     val lastName: Rep[String] = column[String]("LAST_NAME") 
     } 
    } 
    } 


    trait Container2 { 

    self: HasDatabaseConfigProvider[JdbcProfile] with Container1 => 

    import driver.api._ 

    class InsertionTemplate[T <: Table[E], E](tableQuery: TableQuery[T]) { 
     def apply(insertRow:E) = { 
     tableQuery += insertRow 
     } 
    } 

    class Run extends TablesContainer { 
     // specify explicit type parameters. 
     def template = new InsertionTemplate[Members,MembersRow](TableQuery[Members]) 
     template.apply(MembersRow("Joe", "Bloggs")) 
    } 
    }