Select rows based on MAX values of a column in ScalaQuery/SLICK - scala

Question

Say that i have table such as:
UserActions
UserId INT
ActionDate TIMESTAMP
Description TEXT
that holds dates where users perfomed certainActions. If i wanted to get the last action that every user perfomed, i would have to do something like this in SQL:
SELECT *
FROM UserActions,
(
SELECT ua.UserId,
max(ua.ActionDate) AS lastActionDate
FROM UserActions ua
GROUP BY ua.UserId
) AS lastActionDateWithUserId
WHERE UserActions.UserId = lastActionDateWithUserId.UserId
AND UserActions.ActionDate = lastActionDateWithUserId.lastActionDate
Now, assume that i already have a table structure set up in scalaquery 0.9.5 for the UserActions such as:
case class UserAction(userId:Int,actionDate:Timestamp,description:String)
object UserActions extends BasicTable[UserAction]("UserActions"){
def userId = column[Int]("UserId")
def actionDate = column[Timestamp]("ActionDate")
def description = column[String]("Description")
def * = userId ~ actionDate ~ description <> (UserAction, UserAction.unapply _)
}
My question is: in ScalaQuery/SLICK how can i perform such a query?.

Answer 1

I have used Slick 1.0.0 with Scala 2.10.
I defined the objects like this:
case class UserAction(userId: Int, actionDate: Timestamp, description: String)
object UserActions extends Table[UserAction]("UserActions") {
def userId = column[Int]("UserId")
def actionDate = column[Timestamp]("ActionDate")
def description = column[String]("Description")
def * = userId ~ actionDate ~ description <> (UserAction, UserAction.unapply _)
}
Within session block
Database.forURL("jdbc:h2:mem:test1", driver = "org.h2.Driver") withSession {
//...
}
I inserted some sample data
UserActions.insert(UserAction(10, timeStamp, "Action 1"))
UserActions.insert(UserAction(10, timeStamp, "Action 2"))
UserActions.insert(UserAction(10, timeStamp, "Action 3"))
UserActions.insert(UserAction(20, timeStamp, "Action 1"))
UserActions.insert(UserAction(20, timeStamp, "Action 2"))
UserActions.insert(UserAction(30, timeStamp, "Action 1"))
Query(UserActions).list foreach println
First thing to do is create the max query
// group by userId and select the userId and the max of the actionDate
val maxQuery =
UserActions
.groupBy { _.userId }
.map {
case (userId, ua) =>
userId -> ua.map(_.actionDate).max
}
The resulting query looks like this
val result =
for {
ua <- UserActions
m <- maxQuery
if (ua.userId === m._1 && ua.actionDate === m._2)
} yield ua
result.list foreach println