How to handle exceptions in a playframework 2 Async block (scala) -

my controller action code looks this:

  def addingredient() = action { implicit request =>     val boundform = ingredientform.bindfromrequest     boundform.fold(       formwitherrors => badrequest(views.html.admin.index(formwitherrors)),       value => {         async {           val created = service.addingredient(value.name, value.description)           created map { ingredient =>             redirect(routes.admin.index()).flashing("success" -> "ingredient '%s' added".format(ingredient.name))           }            // todo on exception following           // badrequest(views.html.admin.index(boundform.copy(errors = seq(formerror("", ex.getmessage())))))         }       })   } 

my service.addingredient(...) returns promise[ingredient] can throw custom validationexception. when exception thrown return commented code.

currently page renders 500 , in logs have:

play - waiting promise, got error: ingredient name 'test' exists. services.validationexception: ingredient name 'test' exists.

two questions:

• is bad idea return exception service, there better/more scala way handle case?
• how catch exception?

i'd pure functional way have been use type can hold valid , error states.

for that, can use validation form scalaz

but if don't need more scalaz (you ^^), use simple stuff using promise[either[string, ingredient]] result , fold method in async block. is, map convert value when promise redeemed , fold on redeemed.

the point => no exception => every thing typed check :-)

edit

it might need bit of information more, here 2 options: try catch, @kheraud) , either. didn't put validation, ask me if needed. object application extends controller {

  def index = action {     ok(views.html.index("your new application ready."))   }    //using try catch   //  missing wrapping of badrequest promise since async   //    requiring such result. that's done using promise.pure   def test1 = async {     try {       val created = promise.pure(new {val name:string = "myname"})       created map { stuff =>         redirect(routes.application.index()).flashing("success" -> "stuff '%s' show".format(stuff.name))       }     } catch {       case _ => {         promise.pure(redirect(routes.application.index()).flashing("error" -> "an error occurred man"))       }     }   }     //using either (kind of validation)   //  on left side => success value name   val success = left(new {val name:string = "myname"})   //  on right side exception message (could exception instance => keep stack)   val fail = right("bang bang!")    // how use   //   simulate service using promise.pure wraps either result   //    return type of service should promise[either[{val name:string}, string]] in exemple   //   while mapping (that create promise around convert content), folds create right result (redirect in case).   // point => compiled time checked ! , no wrapping pure error case.   def test2(trysuccess:boolean) = async {       val created = promise.pure(if (trysuccess) success else fail)       created map { stuff /* either */ =>         stuff.fold(           /*success case*/s => redirect(routes.application.index()).flashing("success" -> "stuff '%s' show".format(s.name)),           /*the error case*/f => redirect(routes.application.index()).flashing("error" -> f)         )        }    }  }