SLICK 3.0 - multiple queries depending on one another - db.run(action)

Question

I am new to Slick 3 and so far I have understood that db.run are asynchronous call. the .map or .flatMap is run once the Future is returned.

The problem in my code below

Answer 1

The problem in my code below is that all the sub queries do not work (nested db.run)

I suspect you're ending up with nested Future[R] results. I've not investigated that though. Because...

Conceptually speaking, what am I not getting?

The way I'd tackle this is to look at combining DBIO[R]. That might be the concept that helps.

What you're doing is trying to run each action (query, insert...) individually. Instead, combine the individual actions into a single action and run that.

I'd re-write the main logic as this:

  val action: DBIO[Int] = for {
    existingEnterprise <- enterpriseQS.headOption
    rowsAffected       <- existingEnterprise match {
      case Some(n) => salaries += new SalaryRow(0, n.id, salaryItem.worker)
      case None    => createNewEnterprise(salaryItem)
    }
  } yield rowsAffected

For the None case I'd create a helper method:

  def createNewEnterprise(salaryItem: SalaryItem): DBIO[Int] = for {
    eId          <- (enterprises returning enterprises.map(_.id)) += EnterpriseRow(0, salaryItem.enterpriseName)
    rowsAffected <- salaries += new SalaryRow(0, eId, salaryItem.worker)
  } yield rowsAffected

Finally, we can run that:

  val future: Future[Int] = db.run(action)
  // or db.run(action.transactionally)    

  val result = Await.result(future, 2 seconds)

  println(s"Result of action is: $result")

The second half of a blog post I've written talks more about this.

The code I've used is: https://github.com/d6y/so-31471590