如何将具有非默认字段类型的案例类映射到SLICK中的表？ [英] How can I map a case class with non-default field types to a table in Slick?

问题描述

我可以将案例类映射到精巧的数据库表：-

case class SomeTimeStamp(id: Option[Long], timestamp: java.sql.Timestamp )

class TimeStampTable(tag: Tag) extends Table[SomeTimeStamp](tag, "TSTAMP_TABLE") {
  def id    = column[Long]("ID", O.AutoInc, O.PrimaryKey)
  def time  = column[java.sql.Timestamp]("TIME")

  def * = (id.?, time) <> (SomeTimeStamp.tupled, SomeTimeStamp.unapply)
}

Case类包含默认情况下由SLICK转换为数据库类型的字段，因此一切正常。

但是，如果我的Case类中的某个字段不是默认数据库类型，则此操作不起作用。SLICK允许我使用MappdColumnType提供与有效数据库类型之间的隐式转换，因此我尝试了这个方法，请注意，我现在使用的是Java LocalDatetime，而不是SQL时间戳。

case class SomeLocalDate(id: Option[Long], timestamp: java.time.LocalDateTime )

class LocalDateTable(tag: Tag) extends Table[SomeLocalDate](tag, "TLDATE_TABLE") {
import LocalDateTable._
  def id    = column[Long]("ID", O.AutoInc, O.PrimaryKey)
  def time  = column[java.time.LocalDateTime]("TIME")

  def * = (id.?, time) <> (SomeLocalDate.tupled, SomeLocalDate.unapply)
}

object LocalDateTable {
  implicit val localDateTimeToTimestamp = MappedColumnType.base[LocalDateTime, Timestamp](
    { Timestamp.valueOf(_) } ,
    { ts => ts.toLocalDateTime }
  )
}

我已经添加了隐式映射列，但在投影和隐式解析中仍会遇到编译错误 编译错误为：-

[info] Compiling 1 Scala source to ...target/scala-2.11/classes...
[error] db/Tables.scala:92: could not find implicit value for parameter tt: slick.ast.TypedType[java.time.LocalDateTime]
[error]   def time: Rep[LocalDateTime]  = column[java.time.LocalDateTime]("TIME")

如果我修改了def time并添加了类型归属，则会收到不同的错误，请参见下面的内容。

case class SomeLocalDate(id: Option[Long], timestamp: java.time.LocalDateTime )

class LocalDateTable(tag: Tag) extends Table[SomeLocalDate](tag, "TLDATE_TABLE") {
import LocalDateTable._
  def id    = column[Long]("ID", O.AutoInc, O.PrimaryKey)
  def time: Rep[LocalDateTime]  = column[java.time.LocalDateTime]("TIME")

  def * = (id.?, time) <> (SomeLocalDate.tupled, SomeLocalDate.unapply)
}

object LocalDateTable {
  implicit val localDateTimeToTimestamp = MappedColumnType.base[LocalDateTime, Timestamp](
    { Timestamp.valueOf(_) } ,
    { ts => ts.toLocalDateTime }
  )
}

显示此错误：-

[info] Compiling 1 Scala source to ...target/scala-2.11/classes...
[error] db/Tables.scala:92: could not find implicit value for parameter tt: slick.ast.TypedType[java.time.LocalDateTime]
[error]   def time: Rep[LocalDateTime]  = column[java.time.LocalDateTime]("TIME")
[error]                                                                  ^
[error]db/Tables.scala:94: No matching Shape found.
[error] Slick does not know how to map the given types.
[error] Possible causes: T in Table[T] does not match your * projection. Or you use an unsupported type in a Query (e.g. scala List).
[error]   Required level: slick.lifted.FlatShapeLevel
[error]      Source type: (slick.lifted.Rep[Option[Long]], slick.lifted.Rep[java.time.LocalDateTime])
[error]    Unpacked type: (Option[Long], java.time.LocalDateTime)
[error]      Packed type: Any
[error]   def * = (id.?, time) <> (SomeLocalDate.tupled, SomeLocalDate.unapply)
[error]                        ^
[error] two errors found

如果案例类不具有默认支持的数据库类型(例如LocalDateTime)，则必须执行什么操作才能将案例类映射到表？

干杯

推荐答案

经过几天的挣扎，我找到了答案：-/

问题是隐式MappdColumnType是在Table类之后声明的。由于某种原因，这打乱了隐式解析，即使我在表上导入了它。

当我删除Case类并简单地使用Tuples时，我找到了答案。当我这样做时，出现了以下错误

[info] Compiling 1 Scala source to target/scala-2.11/classes...
[error] /db/Tables.scala:100: could not find implicit value for parameter tt: slick.ast.TypedType[java.time.LocalDateTime]
[error]   def time: Rep[LocalDateTime]  = column[java.time.LocalDateTime]("TIME")
[error]                                                                  ^
[error] /db/Tables.scala:102: type mismatch;
[error]  found   : (slick.lifted.Rep[Option[Long]], slick.driver.H2Driver.api.Rep[java.time.LocalDateTime])
[error]     (which expands to)  (slick.lifted.Rep[Option[Long]], slick.lifted.Rep[java.time.LocalDateTime])
[error]  required: slick.lifted.ProvenShape[(Option[Long], java.time.LocalDateTime)]
[error]  Note: implicit value localDateTimeToTimestamp is not applicable here because it comes after the application point and it lacks an explicit result type
[error]   def * : ProvenShape[(Option[Long], LocalDateTime)] = (id.?, time)
[error]                                                        ^

因此，清楚地说，解决方案是将隐式转换放在表定义之上(如果在同一文件中)，或者将其放在另一个文件中并导入，请参阅下面的工作解决方案。谢谢。

case class SomeLocalDate(id: Option[Long], timestamp: java.time.LocalDateTime )

object LocalDateTableConversions {
  implicit val localDateTimeToTimestamp = MappedColumnType.base[LocalDateTime, Timestamp](
    { Timestamp.valueOf(_) } ,
    { ts => ts.toLocalDateTime }
  )
}
import LocalDateTableConversions._

class LocalDateTable(tag: Tag) extends Table[SomeLocalDate](tag, "TLDATE_TABLE") {
  def id    = column[Long]("ID", O.AutoInc, O.PrimaryKey)
  def time: Rep[LocalDateTime]  = column[java.time.LocalDateTime]("TIME")

  def * = (id.?, time) <> (SomeLocalDate.tupled, SomeLocalDate.unapply)
}

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