如何检查List [Option [_]]中是否没有None并返回元素的名称？

Question

I have multiple Option 's. I want to check if they hold a value. If an Option is None , I want to reply to user about this. Else proceed.

This is what I have done:

val name:Option[String]
val email:Option[String]
val pass:Option[String]
val i = List(name,email,pass).find(x => x match{
  case None => true
  case _ => false
})
i match{
  case Some(x) => Ok("Bad Request")
  case None => {
    //move forward
  }
}

Above I can replace find with contains , but this is a very dirty way. How can I make it elegant and monadic?

Edit: I would also like to know what element was None .

Answer 1

Another way is as a for-comprehension:

val outcome = for {
  nm <- name
  em <- email
  pwd <- pass
  result = doSomething(nm, em, pwd) // where def doSomething(name: String, email: String, password: String): ResultType = ???
} yield (result)

This will generate outcome as a Some(result) , which you can interrogate in various ways (all the methods available to the collections classes: map, filter, foreach, etc.). Eg:

outcome.map(Ok(result)).orElse(Ok("Bad Request"))

Answer 2

  val ok = Seq(name, email, pass).forall(_.isDefined)

Answer 3

val response = for {
  n <- name
  e <- email
  p <- pass
} yield {
  /* do something with n, e, p */
}
response getOrElse { /* bad request /* }

Or, with Scalaz:

val response = (name |@| email |@| pass) { (n, e, p) =>
  /* do something with n, e, p */
}
response getOrElse { /* bad request /* }

Answer 4

If you want to reuse the code, you can do

def allFieldValueProvided(fields: Option[_]*): Boolean = fields.forall(_.isDefined)

If you want to know all the missing values then you can find all missing values and if there is none, then you are good to go.

def findMissingValues(v: (String, Option[_])*) = v.collect { 
  case (name, None) => name
}

val missingValues = findMissingValues(("name1", option1), ("name2", option2), ...)

if(missingValues.isEmpty) {
  Ok(...)
} else {
  BadRequest("Missing values for " + missingValues.mkString(", ")))
}

Answer 5

if ((name :: email :: pass :: Nil) forall(!_.isEmpty)) {
} else {
   // bad request
}

Answer 6

I think the most straightforward way would be this:

(name,email,pass) match {
  case ((Some(name), Some(email), Some(pass)) => // proceed
  case _ => // Bad request
}

Answer 7

A version with stone knives and bear skins:

import util._

object Test extends App {

  val zero: Either[List[Int], Tuple3[String,String,String]] = Right((null,null,null))
  def verify(fields: List[Option[String]]) = {
    (zero /: fields.zipWithIndex) { (acc, v) => v match {
        case (Some(s), i) => acc match {
          case Left(_)  => acc
          case Right(t) =>
            val u = i match {
              case 0 => t copy (_1 = s)
              case 1 => t copy (_2 = s)
              case 2 => t copy (_3 = s)
            }
            Right(u)
        }
        case (None, i) =>
          val fails = acc match {
            case Left(f)  => f
            case Right(_) => Nil
          }
          Left(i :: fails)
      }
    }
  }
  def consume(name: String, email: String, pass: String) = Console println s"$name/$email/$pass"
  def fail(is: List[Int]) = is map List("name","email","pass") foreach (Console println "Missing: " + _)

  val name:Option[String] = Some("Bob")
  val email:Option[String]= None
  val pass:Option[String] = Some("boB")

  val res = verify(List(name,email,pass))
  res.fold(fail, (consume _).tupled)
  val res2 = verify(List(name, Some("bob@bob.org"),pass))
  res2.fold(fail, (consume _).tupled)
}

The same thing, using reflection to generalize the tuple copy.

The downside is that you must tell it what tuple to expect back. In this form, reflection is like one of those Stone Age advances that were so magical they trended on twitter for ten thousand years.

  def verify[A <: Product](fields: List[Option[String]]) = {
    import scala.reflect.runtime._
    import universe._
    val MaxTupleArity = 22
    def tuple = {
      require (fields.length <= MaxTupleArity)
      val n = fields.length
      val tupleN = typeOf[Tuple2[_,_]].typeSymbol.owner.typeSignature member TypeName(s"Tuple$n")
      val init = tupleN.typeSignature member nme.CONSTRUCTOR
      val ctor = currentMirror reflectClass tupleN.asClass reflectConstructor init.asMethod
      val vs = Seq.fill(n)(null.asInstanceOf[String])
      ctor(vs: _*).asInstanceOf[Product]
    }
    def zero: Either[List[Int], Product] = Right(tuple)
    def nextProduct(p: Product, i: Int, s: String) = {
      val im = currentMirror reflect p
      val ts = im.symbol.typeSignature
      val copy = (ts member TermName("copy")).asMethod
      val args = copy.paramss.flatten map { x =>
        val name = TermName(s"_$i")
        if (x.name == name) s
        else (im reflectMethod (ts member x.name).asMethod)()
      }
      (im reflectMethod copy)(args: _*).asInstanceOf[Product]
    }
    (zero /: fields.zipWithIndex) { (acc, v) => v match {
        case (Some(s), i) => acc match {
          case Left(_)  => acc
          case Right(t) => Right(nextProduct(t, i + 1, s))
        }
        case (None, i) =>
          val fails = acc match {
            case Left(f)  => f
            case Right(_) => Nil
          }
          Left(i :: fails)
      }
    }.asInstanceOf[Either[List[Int], A]]
  }

  def consume(name: String, email: String, pass: String) = Console println s"$name/$email/$pass"
  def fail(is: List[Int]) = is map List("name","email","pass") foreach (Console println "Missing: " + _)

  val name:Option[String] = Some("Bob")
  val email:Option[String]= None
  val pass:Option[String] = Some("boB")

  type T3 = Tuple3[String,String,String]
  val res = verify[T3](List(name,email,pass))
  res.fold(fail, (consume _).tupled)
  val res2 = verify[T3](List(name, Some("bob@bob.org"),pass))
  res2.fold(fail, (consume _).tupled)

Answer 8

I know this doesn't scale well, but would this suffice?

(name, email, pass) match {
  case (None, _, _) => "name"
  case (_, None, _) => "email"
  case (_, _, None) => "pass"
  case _ => "Nothing to see here"
}