Scala slick groupBy中有字符串连接方法吗?
我试图在一个巧妙的查询中应用Scala slick groupBy中有字符串连接方法吗?,scala,playframework,slick,Scala,Playframework,Slick,我试图在一个巧妙的查询中应用.groupBy var q = (for { user <- Users userSettings <- UserSettings if user.id === userSettings.userId } yield (user, userSettings)).groupBy { case (users, userSettings) => (user.id, userSettings.co
.groupBy
var q = (for {
user <- Users
userSettings <- UserSettings if user.id === userSettings.userId
} yield (user, userSettings)).groupBy {
case (users, userSettings) =>
(user.id, userSettings.controls)
}.map {
case (x, y) => (x._1, y.map(_._2.controls).???)
}
如果不应用groupBy
记录,则如下所示
-----------------------------------------
|User ID |User Controls |
-----------------------------------------
|1 |left |
|1 |right |
|1 |up |
|1 |down |
|2 |left |
|2 |right |
-----------------------------------------
Slick获取您的Scala代码并将其转换为SQL,因此您在Slick中所做的任何事情都必须得到底层SQL的支持。如果您在SQL中搜索与串接字符串相关的类似问题,则您可以。不幸的是,在SQL中执行此类操作是非常重要的。(注意:在某些SQL方言中是可能的。)可能有一些精巧的驱动程序公开特定于SQL方言的函数,或者在SQL查询之后执行某些操作,但您可以简单地执行查询,并在对DB执行后运行groupBy/map,例如:
val q = for {
user <- Users
userSettings <- UserSettings if user.id === userSettings.userId
} yield (user.id, userSettings.controls)
val db = Database.forConfig("h2mem1")
try {
for {
res <- db.run(q.result)
} yield res
.groupBy(_._1)
.map({ case (id, t) => id -> t.map(_._2).mkString(", ") })
} finally db.close
val q=for{
用户不幸的是,没有注意到对此的支持。在这种情况下,我们可以使用带有适当验证和清理的原始查询
假设我有一个名为logs
(id,message,date)的表。我想按日期分组并联系每个分组消息。因此我的查询将是:
def histogram(data: ReqData): Future[Vector[DbHistogramMapper]] = {
var messageWild = s"%${data.phrase}%"
/**Need to write raw query because there is no support for GROUP_CONCAT in slick*/
val query = sql"""SELECT "date" AS date, GROUP_CONCAT("message") AS message FROM "logs" WHERE "date" >= ${data.datetimeFrom} AND "date" <= ${data.datetimeUntil} AND "message" LIKE ${messageWild} GROUP BY "date" """.as[DbHistogramMapper]
db.run(query)
}
我想在运行db.run
IIRC之前应用搜索排序-如果行从db.run
返回时已排序,Scala的groupBy()应保持分组内的顺序。讨论对后端特定聚合函数的支持时存在一个问题:如果您碰巧使用postgres,则slick有一个扩展,它增加了对这些函数的支持:
def histogram(data: ReqData): Future[Vector[DbHistogramMapper]] = {
var messageWild = s"%${data.phrase}%"
/**Need to write raw query because there is no support for GROUP_CONCAT in slick*/
val query = sql"""SELECT "date" AS date, GROUP_CONCAT("message") AS message FROM "logs" WHERE "date" >= ${data.datetimeFrom} AND "date" <= ${data.datetimeUntil} AND "message" LIKE ${messageWild} GROUP BY "date" """.as[DbHistogramMapper]
db.run(query)
}
case class DbHistogramMapper(
date: Timestamp,
message: String
)