How to return a Failure from a RestHelper block?

[Dan Gravell]

I've managed to follow the REST docs so far, but now I want to add a piece of validation that rejects unrecognised Req params. I couldn't see anything that did this in the docs, only the enforcement of manadatory params.

When I try to return a:

ParamFailure("Unrecognized parameters: " + illegalParams, 400)

I get:

[error] /home/gravelld/scala/lift/d6y-lift_24_sbt-0d46974/src/main/scala/com/onemusicapi/api/Api.scala:37: ambiguous implicit values:

[error]  both method conforms in object Predef of type [A]=> <:<[A,A]

[error]  and lazy value convertJsonXmlAble in trait RestHelper of type => PartialFunction[(net.liftweb.http.rest.JsonXmlSelect, net.liftweb.http.rest.JsonXmlAble, net.liftweb.http.Req),net.liftweb.http.LiftResponse]

[error]  match expected type Nothing => net.liftweb.http.LiftResponse

[error]            case _ =>  ParamFailure("Unrecognized parameters: " + illegalParams, 400)

[error]                                   ^

Wider context:

        val illegalParams = S.request.map(_.params.keySet).getOrElse(Set.empty).diff(PARAMS)

        illegalParams toSeq match {

          case Seq() => {

              /* serve request */ : JValue

          } 

          case _ =>  ParamFailure("Unrecognized parameters: " + illegalParams, 400)

        }

I've tried different incantations of Boxes, Seqs and the like but no good.

Dan

[David Pollak]

You can't mix JValue and Failure. If you're going to return a Failure, the return type must be Box[JValue].

In your Seq() block, return a Full(JValue) and the compiler will choose the correct implicit conversion.

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[Dan Gravell]

Thanks David. Strange though, I still get the same thing. I've simplified the code right down:

        val illegalParams = S.request.map(_.params.keySet).getOrElse(Set.empty).diff(PARAMS)

        illegalParams toSeq match {

          case Seq() => {

       Full(JString("hi"))

          } 

          case _ =>  ParamFailure("Unrecognized parameters: " + illegalParams, 400)

        }

[error] /home/gravelld/scala/lift/d6y-lift_24_sbt-0d46974/src/main/scala/com/onemusicapi/api/Api.scala:30: ambiguous implicit values:

[error]  both method conforms in object Predef of type [A]=> <:<[A,A]

[error]  and lazy value convertJsonXmlAble in trait RestHelper of type => PartialFunction[(net.liftweb.http.rest.JsonXmlSelect, net.liftweb.http.rest.JsonXmlAble, net.liftweb.http.Req),net.liftweb.http.LiftResponse]

[error]  match expected type Nothing => net.liftweb.http.LiftResponse

[error]           case _ =>  ParamFailure("Unrecognized parameters: " + illegalParams, 400)

[error]                                  ^

[error] one error found

Maybe I'm missing an import? Apologies if I'm doing something daft.

Dan

[David Pollak]

Sometimes the Scala type inferencer is so weak, it's unbelievable. This code works:

import net.liftweb.http.rest._

import net.liftweb.json._

import net.liftweb.common._

object MyRestThing extends RestHelper {

    serve {

        case "foo" :: x Get _ =>

          (x match {

              case Nil => Full(JString("Hi"))

              case _ => ParamFailure("Hmmm... "+x, 400)

          }) : Box[JValue]

    }

}

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Lift, the simply functional web framework: http://liftweb.net
Code: http://github.com/lift
Discussion: http://groups.google.com/group/liftweb
Stuck? Help us help you: https://www.assembla.com/wiki/show/liftweb/Posting_example_code
 
 
 

[Naftoli Gugenheim]

Can you file a bug?

[Dan Gravell]

It's a bug? I thought it was something I was doing wrong with how I declared the types so the wrong implicit was being picked up... or something.