如何在 Spark2 Scala 中使用匹配大小写模式答案

【问题标题】：How to use match case pattern in Spark2 Scala如何在 Spark2 Scala 中使用匹配大小写模式
【发布时间】：2019-11-25 02:00:44
【问题描述】：

我想在 scala 中使用大小写匹配来定义字符串列表。这是我的代码：

Parametre_mod.targetTableBase match {
              case "DWG_LD_ANOMALIE" => 
                val champs = List("CD_ANOMALIE",
                    "CD_FAMILLE",
                    "LIB_ANOMALIE",
                    "DT_MAJ",
                    "CLASSIFICATION",
                    "NB_REJEUX",
                    "TOP_INDIC_CD_ERREUR", "TOP_COORDONNEE_INVALIDE", "TOP_SUPP", "DT_SUPP")

              case "DWG_LD_NOTIFICATION" =>
                val champs = List(
                    "ID_NOTIFICATION", "ID_ENTITE", "ID_ENTITE_GARANTE", "CD_SYS_APPELANT", "CD_TYPE_DESTINATAIRE", "ID_PERSONNE", "EMAIL_DESTINATAIRE", 
                    "NUM_TEL_DESTINATAIRE", "CD_TYPE_EVENEMENT", "CD_TYPE_NOTIFICATION", "CD_TYPE_DEST_SOURCE", "ID_PERSONNE_DEST_SOURCE", "REF_EXT_DEST_SOURCE", 
                    "EMAIL_DEST_SOURCE", "NUM_TEL_DEST_SOURCE", "ID_PERSONNE_DEST_SOURCE_2", "NB_REJEUX", "TOP_RECYCLAGE", "ID_DOC_STRATEGIE_EDIT", "TOP_SUPP", "DT_SUPP")
            }

            insertion(df, champs, cstProp)

但 Eclipse IDE 表明插入函数中的字段 champs 未定义。请问我怎样才能做到这一点？

【问题讨论】：

标签： scala apache-spark pattern-matching

【解决方案1】：

您在match 表达式中创建的champs 的范围。并且它不能在它之外访问。

您可以分配给champs，如下所示

val champs = Parametre_mod.targetTableBase match {
  case "DWG_LD_ANOMALIE" => List("CD_ANOMALIE",
      "CD_FAMILLE",
      "LIB_ANOMALIE",
      "DT_MAJ",
      "CLASSIFICATION",
      "NB_REJEUX",
      "TOP_INDIC_CD_ERREUR", "TOP_COORDONNEE_INVALIDE", "TOP_SUPP", "DT_SUPP")
  case "DWG_LD_NOTIFICATION" => List(
      "ID_NOTIFICATION", "ID_ENTITE", "ID_ENTITE_GARANTE", "CD_SYS_APPELANT", "CD_TYPE_DESTINATAIRE", "ID_PERSONNE", "EMAIL_DESTINATAIRE",
      "NUM_TEL_DESTINATAIRE", "CD_TYPE_EVENEMENT", "CD_TYPE_NOTIFICATION", "CD_TYPE_DEST_SOURCE", "ID_PERSONNE_DEST_SOURCE", "REF_EXT_DEST_SOURCE",
      "EMAIL_DEST_SOURCE", "NUM_TEL_DEST_SOURCE", "ID_PERSONNE_DEST_SOURCE_2", "NB_REJEUX", "TOP_RECYCLAGE", "ID_DOC_STRATEGIE_EDIT", "TOP_SUPP", "DT_SUPP")
}

希望这会有所帮助！

【讨论】：

【解决方案2】：

您需要在匹配块之外定义“冠军”，以便它在外部也可用 -

var champs:List[String] = List.empty[String]

    Parametre_mod.targetTableBase match {
      case "DWG_LD_ANOMALIE" =>
        champs = List("CD_ANOMALIE",
          "CD_FAMILLE",
          "LIB_ANOMALIE",
          "DT_MAJ",
          "CLASSIFICATION",
          "NB_REJEUX",
          "TOP_INDIC_CD_ERREUR", "TOP_COORDONNEE_INVALIDE", "TOP_SUPP", "DT_SUPP")

      case "DWG_LD_NOTIFICATION" =>
        champs = List(
          "ID_NOTIFICATION", "ID_ENTITE", "ID_ENTITE_GARANTE", "CD_SYS_APPELANT", "CD_TYPE_DESTINATAIRE", "ID_PERSONNE", "EMAIL_DESTINATAIRE",
          "NUM_TEL_DESTINATAIRE", "CD_TYPE_EVENEMENT", "CD_TYPE_NOTIFICATION", "CD_TYPE_DEST_SOURCE", "ID_PERSONNE_DEST_SOURCE", "REF_EXT_DEST_SOURCE",
          "EMAIL_DEST_SOURCE", "NUM_TEL_DEST_SOURCE", "ID_PERSONNE_DEST_SOURCE_2", "NB_REJEUX", "TOP_RECYCLAGE", "ID_DOC_STRATEGIE_EDIT", "TOP_SUPP", "DT_SUPP")
    }
    insertion(df, champs, cstProp)

【讨论】：

这将是 Scala 中的反模式，因为您使用的是 unnecessary var，因为 match 是 表达式 可以返回一个值。
感谢路易斯的建议。