Catching SQL error on future failure in Slick

Question

The code below uses Slick 3.1.x to read a row from a table, attempting to catch any SQL errors. UserDB is the Slick representation of the table, and User is the related object.

This code does not compile in the failure statement with the following error:

type mismatch; found : Unit required: scala.concurrent.Future[Option[user.manage.User]]

How to fix this to catch the SQL error?

   def read (sk: Int): Future[Option[User]] = {
      val users = TableQuery[UserDB]
      val action = users.filter(_.sk === sk).result
      val future = db.run(action)
      future.onSuccess {
        case result =>
              if (!result.isEmpty)
                  Some(result(0))
              else
                  None
      }
      future.onFailure {   // <-- compilation error
          case e => println (e.getMessage)
          None
      }
   }

`onFailure` reigsters a callback and returns `Unit`. Therefore your entire method returns `Unit`. — rethab, Dec 04 '16 at 11:52
Thanks. Assume that on failure I need to write an entry in a log and return `None` (as opposed to return `Some` if the record is read correctly), what should be the approach? — ps0604, Dec 04 '16 at 12:05
Don't use `onFailure` but on of the methods on `Future` that can handle an Exception and still return something. — rethab, Dec 04 '16 at 12:17
My objective is to catch (somehow) the SQL exception, taking into consideration that the function returns a Future with an option. Any ideas? — ps0604, Dec 04 '16 at 12:52

score 9 · Accepted Answer · answered Dec 04 '16 at 13:31

You can use asTry method to catch exception ex into a successful result Failure(ex) and the successful value in Success(v). In your case the following should work.

db.run(action.asTry).map{
  case Failure(ex) => { 
         Log.error(s"error : ${ex.getMessage}") 
         None
        }
  case Success(x) => x
}

As mentioned in the slick documentation, asTry is used to pipeline the exceptions for recovery handling logic.

score 4 · Answer 2 · answered Jan 21 '17 at 12:44

4

You can use the onComplete method of the future.

        future.onComplete{
            case Success(r) ⇒ ...
            case Failure(t) ⇒ log.error("failure in db query " + t.getMessage)
        }

answered Jan 21 '17 at 12:44

ZJ Lyu

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Catching SQL error on future failure in Slick

2 Answers2