我正在嘗試驗證方法的參數是否為空，但找不到解決方案...有人可以告訴我該怎么做嗎？我正在嘗試這樣的事情： def buildNormalCategory(user: User, parent: Category, name: String, description: String): Either[Error,Category] = { val errors: Option[String] = for { _ <- Option(user).toRight("User is mandatory for a normal category").right _ <- Option(parent).toRight("Parent category is mandatory for a normal category").right _ <- Option(name).toRight("Name is mandatory for a normal category").right errors : Option[String] <- Option(description).toRight("Description is mandatory for a normal category").left.toOption } yield errors errors match { case Some(errorString) => Left( Error(Error.FORBIDDEN,errorString) ) case None => Right( buildTrashCategory(user) ) } }
3 回答
largeQ
TA貢獻2039條經驗 獲得超8個贊
我完全支持Ben James的建議，為產生null的api做包裝。但是編寫該包裝器時仍然會遇到相同的問題。所以這是我的建議。
為什么單子為什么要理解？IMO過于復雜。這是您可以執行的操作：
def buildNormalCategory
( user: User, parent: Category, name: String, description: String )
: Either[ Error, Category ]
= Either.cond(
!Seq(user, parent, name, description).contains(null),
buildTrashCategory(user),
Error(Error.FORBIDDEN, "null detected")
)
或者，如果您堅持讓錯誤消息存儲參數名稱，則可以執行以下操作，這將需要更多樣板：
def buildNormalCategory
( user: User, parent: Category, name: String, description: String )
: Either[ Error, Category ]
= {
val nullParams
= Seq("user" -> user, "parent" -> parent,
"name" -> name, "description" -> description)
.collect{ case (n, null) => n }
Either.cond(
nullParams.isEmpty,
buildTrashCategory(user),
Error(
Error.FORBIDDEN,
"Null provided for the following parameters: " +
nullParams.mkString(", ")
)
)
}
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