scala - Slick 3.0.0: How to query one-to-many / many-to-many relations -

basically same question has been asked year ago slick 2.x (scala slick one-to-many collections). i'm wondering if there has progression been made release of reactive slick.

let's example have 3 tables. library, book , library_to_book library has many books. want list of libraries books. in scala seq[(library, seq[book])]. query have follows:

val q = (for {   l   <- libraries   ltb <- librarytobooks if l.id === ltb.libraryid   b   <- books if ltb.bookid === b.id } yield (l, b) db.run(q.result).map( result => ??? ) 

results in case of type seq[(library, book)]. how have change query result of type seq[(library, seq[book])] instead? "slick way" of writing such queries?

imo code looks fine. depends on feels more readable you. alternatively, can use join well:

val findbooksquery = libraries   .join(librarytobooks).on(_.id === _.libraryid)   .join(books).on(_.id === _._2.bookid)   .result  val action = (for {   booksresult <- findbooksquery } yield {   booksresult.map { row =>     val (librarytablerow, librarytobookstablerow) = row._1     val bookstablerow = row._2     // todo: access data rows , construct desired ds   } }  db.run(action) 

you can groupby on particular key kind of data structure looking for. in case, more evolved join across 3 tables. example, add following query:

val findbooksquery = libraries   .join(librarytobooks).on(_.id === _.libraryid)   .join(books).on(_.id === _._2.bookid)   // group libraries.id   .groupby(_._1.id)   .result