scala – 如何将派生变量添加到ResultSet

case class Campaign(id: Int,campaign_mode_id: Int,name: String)

class Application @Inject()(db: Database) extends Controller {

  val campaign = {
    get[Int]("campaign.id") ~
    get[Int]("campaign.campaign_mode_id") ~
    get[String]("campaign.name") map {
      case id ~ campaign_mode_id ~ name  => Campaign(id,campaign_mode_id,name)
    }
  }

  def index = Action {
    val data : List[Campaign] = db.withConnection { implicit connection =>
      SQL("SELECT id,name FROM campaign").as(campaign.*)
    }

    Ok(Json.toJson(data))
  }
}

它产生的结果可能如下所示：

[
    {
        id: 2324,campaign_mode_id: 13,name: "ABC"
    },{
        id: 1324,campaign_mode_id: 23,name: "ABCD"
    }   
]

现在,如果广告系列表格中有一个额外的日期字段,例如广告系列启动时引用的start_on,该怎么办？或者另一个名为num_followers的字段是一个整数,指的是关注者的数量？

并且假设我想在运行数据库查询之后和返回我的JSON之前进行一些计算.例如,我想要包含一个参考最新广告系列的started_on日期的latest_compaign_date.或者说我想要包含一个average_num_followers,它引用了所有广告系列的平均关注者数量.

我的最终结果如下：

{
    latest_compaign_date: 12 Dec 2018,average_num_followers: 123,campaigns: [
        {
            id: 2324,name: "ABC"
        },{
            id: 1324,name: "ABCD"
        }   
    ]
}

我知道,对于我给出的示例,我最好在我的数据库查询中进行这些计算,而不是在我的应用程序代码中.但是,如果我必须做一些非常复杂的事情并且想在我的应用程序代码中出于某种原因这样做呢？我应该如何修改我的ResutSetParser来实现这一点？

以下是我尝试过的几种方法：

不要使用ResultSetParser而是手动执行所有操作

case class CampaignData(newestCampaignDate: Long,newestCampaignId: Long,averageNumFollowers: Float,campaigns: Seq[Campaign])

  def aggregater(rows: Seq[Row]): CampaignData = {
    val newestCampaignDate: Long = getNewestDate(rows)
    val newestCampaignId: Long = getNewestCampaign(rows)
    val averageNumFollowers: Float = getAverageNumFollowers(rows)

    val campaigns: Seq[Campaign] = rows.map(row => {
      val rowMap: Map[String,Any] = row.asMap

      Campaign(
        rowMap("campaign.id").asInstanceOf[Int],rowMap("campaign.campaign_mode_id") match { case None => 0 case Some(value) => value.asInstanceOf[Int]},rowMap("campaign.name") match { case None => "" case Some(value) => value.asInstanceOf[String]}
      )
    })

    CampaignData(newestCampaignDate,newestCampaignId,averageNumFollowers,campaigns)
  }

  def index = Action {
    val data : Seq[Row] = db.withConnection { implicit connection =>
      SQL("SELECT id,name,started_on,num_followers FROM campaign")
    }

    Ok(Json.toJson(aggregater(data)))
  }

这种方法闻起来很糟糕,因为必须使用asInstanceOf来处理每个字段并且匹配非常繁琐且真实地感觉不安全.而且直觉上,我觉得Anorm应该有更好的东西,因为我可能不是第一个遇到这个问题的人.

将ResultSetParser与另一个函数结合使用

case class Campaign(id: Int,name: String)
case class CampaignData(newestCampaignDate: Long,campaigns: Seq[Campaign])

val campaign = {
  get[Int]("campaign.id") ~
  get[Int]("campaign.campaign_mode_id") ~
  get[Int]("campaign.num_followers") ~
  get[Long]("campaign.started_on") ~
  get[String]("campaign.name") map {
    case id ~ campaign_mode_id ~ num_followers ~ started_on ~ name  => Map(
      "id" -> id,"campaign_mode_id" -> campaign_mode_id,"num_followers" -> num_followers,"started_on" -> started_on,"name" -> name
    )
  }
}

def index = Action {
  val data : Map[String,Any] = db.withConnection { implicit connection =>
    SQL("SELECT id,num_followers FROM campaign").as(campaign.*)
  }

  Ok(Json.toJson(aggregator(data)))
}

def aggregator(data: Map[String,Any]): CampaignData = {
  val newestCampaignDate: Long = getNewestDate(data)
  val newestCampaignId: Long = getNewestCampaign(data)
  val averageNumFollowers: Float = getAverageNumFollowers(data)
  val campaigns: Seq[Campaign] = getCampaigns(data)

  CampaignData(newestCampaignDate,campaigns)
}

这种方法在我不必处理isInstanceOf的意义上更好,但是那时必须处理中间Map存在更大的问题.它使得所有的getter函数(例如getCampaigns)变得更加复杂.我觉得Anorm必须提供一些我不知道的开箱即用的东西.