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如何用EitherT映射一个选项以供理解

scala-cats scala

0

agusgambina · 技术社区 · 7 年前

嗨,我正在尝试执行一个类似于

(for {
  player <- playerRepository.findById(playerId) // findById returns EitherT[Future, String, Player]
  teamOpt <- teamRepository.findByPlayer(playerId) // findByPlayer returns EitherT[Future, String, Option[Team]]
  playedMatches <- teamOpt.map(team => playedMatchesRepository.findByTeamId(team.id)) // findByTeamId returns EitherT[Future, String, Seq[PlayedMatches]]
} yield (
  player,
  teamOpt,
  playedMatches
)).fold(
  error => {
    logger.error(s"all error: $error")
    Left(error)
  },
  tuple => {
    logger.debug(s"get success -> $tuple")
    Right(playerDetailResponse(tuple._1, tuple._2, tuple._3))
  }
)

playedMatches <- teamOpt.map(team => playedMatchesRepository.findByTeamId(team.id))

当我编译项目时,我得到了以下错误

[error] /Users/agusgambina/code/soccer/app/services/impl/PlayerServiceImpl.scala:28:17: type mismatch;
[error]  found   : Option[(models.Player, Option[models.Team], cats.data.EitherT[scala.concurrent.Future,String,Seq[models.PlayedMatches]])]
[error]  required: cats.data.EitherT[scala.concurrent.Future,?,?]
[error]       playedMatches <- teamOpt.map(team => playedMatchesRepository.findByTeamId(team.id))
[error]                 ^
[error] one error found

1 回复 | 直到 7 年前

1

FerranJr 7 年前

playedMatches <- teamOpt.map(team => playedMatchesRepository.findByTeamId(team.id)) // findByTeamId returns EitherT[Future, String, Seq[PlayedMatches]]

在这里,您将获得一个选项[EitherT[Future,String,Seq[PlayedMatches]]],该选项不与您用作单子的EitherT[Future,String,?组成,以便于理解。

您可以选择在teamOpt上实际使用折叠。

teamOpt.fold(EitherT(Future.successful(Left("Team not Found"): Either[String, Team]))){ team => playedMatchesRepository.findByTeamId(team.id) }

希望能有帮助

使现代化 如果是空的情况,请成功,并愉快地返回空序列:

teamOpt.fold(
  EitherT(Future.successful(Right(Seq()): Either[String, Seq[PlayedMatches]))
){ team =>
  playedMatchesRepository.findByTeamId(team.id) 
}