如何访问返回Option对象的方法？

Question

我必须调用返回Option[List[Obj]]的方法。

打电话后，我需要遍历List并打印Obj属性。

object Tester{
  def main(args:Array[String]) {
    val ymlFilename ="some.yml";
  val entities: Option[QueryEntities] =  InputYamlProcessor.process(ymlFilename)

        for( e: QueryEntities  <- entities ){
          /// this is not working
           //How to access the columnFamily, fromData and toDate ?
        }
  }

完整样本

https://gist.github.com/shatestest/fdeaba767d78e171bb6c08b359fbd1bf

Answer 1

最具标志性的方法是使用scala来解包值，即使用模式匹配来解包值。

entities match {
    case Some(queryEntities: QueryEntities) => 
      queryEntities.entities.foreach { case e =>
        println(e.columnFamily)
        println(e.fromDate.getOrElse("defaultFromDateHere")
        println(e.toDate.getOrElse("defaultToDateHere"))
      }
    case None => println("No value")
}