How to return Future of Either[Throwable,Int] from a Scala Slick Query output

Question

I am a beginner in scala , I am using slick and postgres for one of my model API Below is my function that takes Id: String as input and forms a left inner join query which returns matching Ids(String) from DB table.

def getCountByID(
    Id: String
  ): Future[Either[Throwable, Int]] = {
    val innerJoin = for {
      (rel,a) <- executors joinLeft executors on ( (e1, e2) => {
    e1.column1 === e2.column1 && e1.column2 === e2.column2
    } ) if rel.id === Id
  } yield a.map(_.id)

  db.run(innerJoin.result) # Seq of options => FixedSqlStreamingAction[Seq[Option[String]],Option[String],dbio.Effect.Read]

  }

The db.run gives me a Seq of options . I want to return a Future with Either length of Ids or some throwable exception . How can I achieve the same here.

Answer 1

The type Either[Throwable, Int] is basically a poorer version of Try[Int] so I strongly suggest using Try here. You can call asTry on result and you will get Future[Try[Seq[_]]:

db.run(innerJoin.result.asTry)

If you want a count then you should do that in the database rather than outside:

db.run(innerJoin.length.result.asTry)

This should give Future[Try[Int]].

If you really need Future[Either[Throwable, Int]] then you can call toEither on the Try.