[2.0] Scala Json Generics & creating a document with Reactive Mongo

[Alex Jarvis]

Surely there has to be an easier way?

I've just read through the documentation here: http://www.playframework.org/documentation/2.0.3/ScalaJsonGenerics

and although useful, what I really want to do is just define my 'case class' and have Play automagically map the Json to this object, throwing a validation error if it does not match the attributes etc.

Has anyone else thought about this?

What I am trying to achieve is a nice way to insert a mongodb document with Reactive Mongo. I've had a look at the examples and they seem to just pass in a JSValue straight from the request body using parse.json. This is not really desirable as I want to validate the Json sent from the client before blindly inserting a document with it.

I see that I can define an implicit BSONWriter for my case class and also define a reads method as mentioned in the Scala Json Generics documentation, but this means that I'll then be providing custom boilerplate code to map from my Json -> Scala objects -> BSON

Maybe I just need a neat way of validating the Json that has already been serialised for me using the parse.json body parser?

Any help on this would be greatly appreciated. I am just looking for a neat design pattern, or maybe I've missed something in the helper classes provided with Reactive Mongo or the respective helper classes.

Cheers,

Alex

[Pascal Voitot Dev]

Oh yes we've thought about that :)
It's one of the new features in Play2.1 : Json validators / combinators !
The new JSON API is already present in Play2 master but we are still working on it.

If you want to have a glance at this new API, have a look at my recent article:
http://mandubian.com/2012/09/08/unveiling-play-2-dot-1-json-api-part1-jspath-reads-combinators/
I should write Part2 soon (still working a bit on the API)

You can have a look at this very simple sample: https://github.com/zenexity/Play-ReactiveMongo/tree/master/samples/Play-ReactiveMongo-Sample

We are working on enhancing all of this for future Play2.1 so API is still draft.

Thanks
Pascal

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[Alex Jarvis]

Sweet Jesus

[Alex Jarvis]

Thanks a lot for this. It's amazing work what you're doing with the API, it was exactly what I was searching for :)

I have a slight problem getting the validate.fold example working however as I have it wrapped by Async as required by Reactive Mongo.

e.g.

def create = Action(parse.json) { request =>

    Async { 

      val json = request.body

      json.validate[User].fold(

        valid = (res => 

          collection.insert[JsValue](res).map(lastError => 

            Ok("Mongo LastError:%s".format(lastError)))

        ),

        invalid = ( e => BadRequest(e.toString) )

      )

    }

  }

Provides the error on the last line (invalid = ..):

"type mismatch; found : play.api.mvc.SimpleResult[String] required: 

scala.concurrent.Future[play.api.mvc.Result]"

Is there a way to provide a Future of a BadRequest?

Also, for my userReads implicit val, I had to specify "(User.apply _)" e.g.

implicit val userReads = (

    (__ \ "email").read[String] and

    (__ \ "firstName").read[String] and

    (__ \ "lastName").read[String]

  )(User.apply _)

And if I change it to just have (User) at the end, as suggested it spurts out the following:

"- overloaded method value apply with alternatives: [B](f: B => (java.lang.String, java.lang.String, String))(implicit fu: 

play.api.libs.json.util.ContravariantFunctor[play.api.libs.json.Reads])play.api.libs.json.Reads[B] <and> [B](f: (java.lang.String, java.lang.String, String) => B)(implicit fu: 

play.api.libs.json.util.Functor[play.api.libs.json.Reads])play.api.libs.json.Reads[B] cannot be applied to (models.User.type)"

 (I have declared the implicit val inside the User object, as there was not a complete example and I figured it didn't belong in the Controller).

On Tuesday, 25 September 2012 12:34:38 UTC+1, Pascal wrote:

[Pascal Voitot Dev]

below

On Tue, Sep 25, 2012 at 3:17 PM, Alex Jarvis <alex.j...@gmail.com> wrote:

Thanks a lot for this. It's amazing work what you're doing with the API, it was exactly what I was searching for :)

Thanks ;)
 

I have a slight problem getting the validate.fold example working however as I have it wrapped by Async as required by Reactive Mongo.

e.g.

def create = Action(parse.json) { request =>

    Async { 

      val json = request.body

      json.validate[User].fold(

        valid = (res => 

          collection.insert[JsValue](res).map(lastError => 

            Ok("Mongo LastError:%s".format(lastError)))

        ),

        invalid = ( e => BadRequest(e.toString) )

      )

    }

  }

You should send a Pure Future[Result] such as :

        invalid = ( e => Future(BadRequest(e.toString)) )

This is Scala2.10 Future ;)
 

Provides the error on the last line (invalid = ..):

"type mismatch; found : play.api.mvc.SimpleResult[String] required: 

scala.concurrent.Future[play.api.mvc.Result]"

Is there a way to provide a Future of a BadRequest?

Also, for my userReads implicit val, I had to specify "(User.apply _)" e.g.

implicit val userReads = (

    (__ \ "email").read[String] and

    (__ \ "firstName").read[String] and

    (__ \ "lastName").read[String]

  )(User.apply _)

And if I change it to just have (User) at the end, as suggested it spurts out the following:

"- overloaded method value apply with alternatives: [B](f: B => (java.lang.String, java.lang.String, String))(implicit fu: 

play.api.libs.json.util.ContravariantFunctor[play.api.libs.json.Reads])play.api.libs.json.Reads[B] <and> [B](f: (java.lang.String, java.lang.String, String) => B)(implicit fu: 

play.api.libs.json.util.Functor[play.api.libs.json.Reads])play.api.libs.json.Reads[B] cannot be applied to (models.User.type)"

 (I have declared the implicit val inside the User object, as there was not a complete example and I figured it didn't belong in the Controller).

If you define outside the User object?

How is defined your User class? the syntax with "(User)" is only for case classes...

Pascal
 

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[Alex Jarvis]

I think I need to download Scala 2.10 for that Future to work.. is that correct? I built 2.1-SNAPSHOT using 2.9.2 I think, so maybe this will cause issues (or does it not use scala on my path?)

This is my User case class and object:

case class User(

  email: String,

  firstName: String,

  lastName: String

)

  

object User { 

  implicit val userReads = (

    (__ \ "email").read[String] and

    (__ \ "firstName").read[String] and

    (__ \ "lastName").read[String]

  )(User.apply _)

}

[Pascal Voitot Dev]

No you don't need scala 2.10...
Play 2.1-SNAPSHOT build is autonomous normally using "./build.sh"
And once built, you can use it directly without any local install of Scala...
Don't put Scala libs on your path, Play brings everything!

Pascal

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