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Accepted
Andrew_STOP_RU_AGRESSION_IN_UA
Asked:2020-04-03 19:07:13 +0800 CST2020-04-03 19:07:13 +0800 CST

帮助在 Scala 中重写 LINQ 查询

  • 772

原始查询：

var rez = planes
    .Where(b => (b.FlDate >= dateFrom) && (b.FlDate <= dateTo))
    .GroupBy(i => i.Destination)
    .Select(g => new { Destination = g.Key, Count = g.Count() })
    .ToList();

斯卡拉代码：

var rez = planes
  .filter( _.FlDate.getMillis >= dateFrom.getMillis)
  .filter(_.FlDate.getMillis <= dateTo.getMillis)
  .groupBy(_.Destination)
  .flatMap( new { Destination:String = _.Key, Count = _.Count() })

问题出在线上

.flatMap( new { Destination:String = _.Key, Count = _.Count() })

我根本斗不过她。

也就是说，我应该以任何带有两个参数的匿名对象列表结束：Count和Destination。

scala

1 个回答

  1. Best Answer

    答案：正确的查询是：

    如果不需要命名对象的属性：

    val rez: Map[String, Int] = planes
      .filter(logRow => logRow.FlDate.isAfter(dateFrom) && logRow.FlDate.isBefore(dateTo))
      .groupBy(_.Destination)
      .map { case (location, logRows) => (location, logRows.length) }

    或者如果您需要命名对象的属性：

    val rez = planes
      .filter(logRow => logRow.FlDate.isAfter(dateFrom) && logRow.FlDate.isBefore(dateTo))
      .groupBy(_.Destination)
      .map {
        case (location, logRows) => new {
          val destination = location;
          val count = logRows.length
        }
      }
    • 1

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