Scala Slick 3：计数行并获取行

【问题标题】：Scala Slick 3: Count Rows and get rowScala Slick 3：计数行并获取行
【发布时间】：2015-08-06 10:52:07
【问题描述】：

我不知道如何用 Slick (3) 计数。

val posts = for {
  p <- Posts.query if p.receiver === userId
  comments <- Comments.query if comments.postId === p.id
  author <- Users.query if p.author === author.id
  receiver <- Users.query if p.receiver === receiver.id
} yield (p, comments, author, receiver)

具有以下关系

Posts : Author : Receiver : Comments
1 : 1 : 1 : N

结果应该是：

Future[Seq[(Post, User, User, Int)]]

int 是 cmets grouped by Posts 的计数

有什么建议吗？

【问题讨论】：

标签： sql scala slick slick-3.0

【解决方案1】：

您需要按帖子、作者和收件人以及地图对结果进行分组，以通过计数来聚合 cmets。

val posts = (for {
  p <- Posts.query if p.receiver === userId
  comment <- Comments.query if comments.postId === p.id
  author <- Users.query if p.author === author.id
  receiver <- Users.query if p.receiver === receiver.id
} yield (p, comment, author, receiver)) //So far thats your current query
  .groupBy({ //Group by post, author and receiver
      case (post, comment, author, receiver) =>
          (post, author, receiver)
  })
  .map({ //Aggregate your comments (second argument in tuple) and count them
      case ((post, author, receiver), list) => { 
          (post, author, receiver, list.map(_._2).count))
      }
  })

目前在移动设备上，所以这可能无法编译，但你应该明白了。

【讨论】：