compilation error involving effect type in DBIOAction

[Ambrose Laing]

Hi all,
I adapted some code from: http://blog.scalac.io/2015/07/09/slick-3-overview.html
and obtained the following:

---------------
  private val usersQuery: TableQuery[Users] = TableQuery[Users]

  private val createAction: DBIO[Unit] =
    usersQuery.schema.create

  private val tablesExistAction: DBIO[Boolean] = MTable.getTables.map { tables =>
    val names = Vector(usersQuery.baseTableRow.tableName)
    names.intersect(tables.map(_.name.name)) == names
  }

  def createIfNotExist(): Future[Unit] =
    db.run(
      tablesExistAction.flatMap(
        exist => if (!exist)
          createAction
        else
          SuccessAction{}
      ))
-----------

And now I have a compilation error as follows:

-----------
[error] /home/mylogin/my/project/app/model/Models.scala:173: type mismatch;
[error]  found   : Boolean => slick.dbio.DBIOAction[Unit,slick.dbio.NoStream,Nothing]
[error]  required: Boolean => slick.dbio.DBIOAction[Unit,slick.dbio.NoStream,E2]
[error]         exist => if (!exist)
[error]               ^
[error] one error found
-------------

The types match except for the third type parameter in the DBIOAction.
I would appreciate any pointers on how to fix this error.

Thanks,

Ambrose

[Ambrose Laing]

Update: I'm using Play 2.4.2, Slick 3.0.2 and play-slick 1.0.1.

[Richard Dallaway]

I think you should be able to help the compiler out by giving the types on flatMap. Something like...

tablesExistAction.flatMap[Boolean, dbio.NoSream, dbio.Effect.All] { exists => ... etc }

Apologies I've not had a chance to create an example project an try that out, though.  I'd like to know if it, or something like it, works for you.

Richard

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[Ambrose Laing]

Hi Richard,
Your suggestion solved the problem, with the very minor tweak of replacing Boolean with Unit (as the first type param). 
Thanks for the help!,
Ambrose

[Richard Dallaway]

Great - thanks for letting me know.

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