Slick 中的 Scala 投影仅用于一列

本文介绍了Slick 中的 Scala 投影仅用于一列的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 我正在关注 自动递增字段的流畅文档示例 我在创建 映射投影 那......好吧，只有一列.case class UserRole(id: Option[Int], role: String)object UserRoles extends Table[UserRole]("userRole") {def id = column[Int]("ID", O.PrimaryKey, O.AutoInc)def role = column[String]("ROLE")//...def * = id.?~ 角色 <>(UserRole, UserRole.unapply _)//下一行错误输出def forInsert = 角色 <>({t => UserRole(None, t._1)}, {(r: UserRole) => Some((r.role))}) 返回 id}错误是值 不是 scala.slick.lifted.Column[String] 的成员"我也认为像这样设计我的模式会更有效:case class UserRole(role: String)object UserRoles extends Table[UserRole]("userRole") {def role = column[Int]("ROLE", O.PrimaryKey)//...def * = 角色 <>(UserRole, UserRole.unapply _)}但随后我也开始收到与上述相同的错误.值 不是 scala.slick.lifted.Column[String] 的成员"我到底在做什么?我是否因为只有一列而不再有 projection ?如果是这样，我应该做什么? 解决方案 这是 Slick 的一个已知问题；映射投影不适用于单列.参见 https://github.com/slick/slick/issues/40>幸运的是，您的代码不需要映射投影即可工作.只需省略 <> 之后的所有内容.参见 scala slick 方法我目前无法理解对预测的一个很好的解释.它包括您开始工作所需的信息.I'm following the Slick documentation example for autoincrementing fields and I'm having trouble creating a mapped projection that ... well, only has one column.case class UserRole(id: Option[Int], role: String)object UserRoles extends Table[UserRole]("userRole") { def id = column[Int]("ID", O.PrimaryKey, O.AutoInc) def role = column[String]("ROLE") // ... def * = id.? ~ role <> (UserRole, UserRole.unapply _) // NEXT LINE ERRORS OUT def forInsert = role <> ({t => UserRole(None, t._1)}, {(r: UserRole) => Some((r.role))}) returning id}The error is "value <> is not a member of scala.slick.lifted.Column[String]"I also thought it'd be more efficient to design my schema like so:case class UserRole(role: String)object UserRoles extends Table[UserRole]("userRole") { def role = column[Int]("ROLE", O.PrimaryKey) // ... def * = role <> (UserRole, UserRole.unapply _)}But then I start getting the same error as above, too. "value <> is not a member of scala.slick.lifted.Column[String]"What am I really doing? Do I just not have a projection anymore because I only have one column? If so, what should I be doing? 解决方案 This is a known issue with Slick; mapped projections do not work with a single column. See https://github.com/slick/slick/issues/40Luckily, you don't need a mapped projection for your code to work. Just omit everything after and including the <>. See scala slick method I can not understand so far for a great explanation of projections. It includes the information you need to get going. 这篇关于Slick 中的 Scala 投影仅用于一列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！