Slick. Select and then update selected rows - scala

Question

I want to select some rows, update them and return updated values, but I don't understand how can I do it with Slick. Here is an example. I want to select all tasks which are awaiting execution, lock them, change statuses to in progress and return updated tasks:
object Test {
case class Task(id: Int, status: String)
class TaskTable(tag: Tag) extends Table[Task](tag, "tasks") {
def id = column[Int]("id")
def status = column[String]("status")
def * = (id, status) <>(Task.tupled, Task.unapply)
}
val tasks = TableQuery[TaskTable]
def selectWaitingTasksAndChangeStatus(): Seq[Task] = {
tasks.filter(_.status === "awaitingExecution").forUpdate
// Here I want to change status to "inProgress" and
// return tasks to client code with "inProgress" status
}
}

Answer 1

Is this the thing you're looking for?
import scala.concurrent.Await
import scala.concurrent.duration.Duration
def selectWaitingTasksAndChangeStatus(): Seq[Task] = {
val selectAction = tasks.filter(_.status === "inProgress").result
val updateAction = tasks.filter(_.status === "awaitingExecution").map(_.status).update("inProgress")
val combinedAction = for {
tasksBeforeUpdate <- selectAction
_ <- updateAction
tasksAfterUpdate <- selectAction
} yield tasksAfterUpdate.diff(tasksBeforeUpdate)
Await.result(db.run(combinedAction.transactionally), Duration.Inf)
}
Since you'd like to get Seq[Task] from that method, you have to synchronously wait for the result from the database. Asynchronous solution would require Future[Seq[Task]] as the returned type.