[2.1 master] Please help with Json.reads Json.writes macros

[Daniel Dietrich]

Hi,

according to Json.scala there are two macros: Json.reads and Json.writes.

Has anyone an idea / could give me a hint, please, why the following code does not work? (See comments for compiler errors.)

Thanks in advance

Daniel

import play.api.libs.json.Json

case class User(name: String, age: Int, active: Boolean)

object JsonTest extends App {

  implicit val userReads = Json.reads[User] // not found: value JsPath

  implicit val userWrites = Json.writes[User] // not found: value JsPath

  val daniel = User("daniel", 37, true)

  /*

   * Multiple markers at this line

   * - not enough arguments for method toJson: (implicit tjs: play.api.libs.json.Writes[User])play.api.libs.json.JsValue.

   *   Unspecified value parameter tjs.

   * - No Json deserializer found for type User. Try to implement an implicit Writes or Format for this type.

   */

  val userJson = Json.toJson(daniel)

  val user = Json.fromJson(userJson)

  assert(user == daniel)

}

[Pascal Voitot Dev]

Please import a few more stuff in your scope. You need the default implicits...

import play.api.libs.json._
import play.api.libs.json.util._
import play.api.libs.json.Reads._
import play.api.libs.json.Writes._

regards
Pascal

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[Daniel Dietrich]

thx - I will try it

[Daniel Dietrich]

Merci bien! It works.

But I must not import the Reads._ stuff, otherwise I got the following error at Json.fromJson(userJson):

Multiple markers at this line

- diverging implicit expansion for type play.api.libs.json.Reads[T] starting with method ArrayReads in trait DefaultReads

- ambiguous implicit values:  both value userReads in object json of type => play.api.libs.json.Reads[json.User]  and object IntReads in trait DefaultReads of type play.api.libs.json.Reads.IntReads.type  match expected type play.api.libs.json.Reads[T]

- diverging implicit expansion for type play.api.libs.json.Reads[T] starting with method ArrayReads in trait DefaultReads

- not enough arguments for method fromJson: (implicit fjs: play.api.libs.json.Reads[T])play.api.libs.json.JsResult[T]. Unspecified value parameter fjs.

Anyway, as of this discussion the json stuff is currently subject of refactoring...

import play.api.libs.json._

import play.api.libs.json.util._

// import play.api.libs.json.Reads._

import play.api.libs.json.Writes._

object json {

  case class User(name: String, age: Int, active: Boolean)

  implicit val userReads = Json.reads[User]       //> userReads  : play.api.libs.json.Reads[json.User] = play.api.libs.json.Reads$

                                                  //| $anon$8@518f5824

  implicit val userWrites = Json.writes[User]     //> userWrites  : play.api.libs.json.OWrites[json.User] = play.api.libs.json.OWr

                                                  //| ites$$anon$2@388ee016

  val daniel = User("daniel", 37, true)           //> daniel  : json.User = User(daniel,37,true)

  val userJson = Json.toJson(daniel)              //> userJson  : play.api.libs.json.JsValue = {"name":"daniel","age":37,"active":

                                                  //| true}

  val user = Json.fromJson(userJson)              //> user  : play.api.libs.json.JsResult[json.User] = JsSuccess(User(daniel,37,tr

                                                  //| ue),)

  user.get == daniel                              //> res0: Boolean = true

[Pascal Voitot Dev]

Do you mean that if you import both Reads._ and Writes._ you get errors?

Pascal

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[Daniel Dietrich]

yes.

I compiled Play20 master with scala 2.10.0-RC1

and run eclipse juno sr1 with scala ide (which uses scala 2.10.0-RC2).

My eclipse project files are created with the 'play eclipse' command.

- Daniel

[Pascal Voitot Dev]

Strange!
I'm going to test that!

thanks
Pascal

- Daniel

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[Pascal Voitot Dev]

Hello all,

After some macro headaches, I finally succeeded in adding fully qualified classes everywhere and also embedding functional.syntax._ import in generated code.

Everything is in this pull req:
https://github.com/playframework/Play20/pull/546

Now you can just write:

import play.api.libs.json.Json

implicit val userReads = Json.reads[User]

Nothing more is required from the user except the implicits he created himself.

regards
Pascal

[Daniel Dietrich]

Wow - thank you very much!

 

Daniel

[Pascal Voitot Dev]

Daniel,
Please test again with your case and let see if you still have a pb!

Pascal

Le 16 nov. 2012 17:42, "Daniel Dietrich" <cafe...@googlemail.com> a écrit :

Wow - thank you very much!

 

Daniel

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[Daniel Dietrich]

Pascal,

could you give me a hint how I get the changes of your pull request to my local git repository?

[Daniel Dietrich]

ok, of cause I clone the forked repo git://github.com/mandubian/Play20.git

[Pascal Voitot Dev]

Git clone master
Go in framework Dir
Run ./build
Then "publish-local" in console
Then point your play alias to bin/play
Run your project with this play

Pascal

Le 16 nov. 2012 18:58, "Daniel Dietrich" <cafe...@googlemail.com> a écrit :

Pascal,

could you give me a hint how I get the changes of your pull request to my local git repository?

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[Daniel Dietrich]

It works great! Tested it as Scala App and as Worksheet.

Adding import play.api.libs.json.Writes._ does not affect the code.

Adding import play.api.libs.json.Reads._ does introduce the following compile time error (which should be ok!):

Multiple markers at this line

- ambiguous implicit values: both value userReads in object JsonTest of type => play.api.libs.json.Reads[User] and object IntReads in trait DefaultReads of 

type play.api.libs.json.Reads.IntReads.type match expected type play.api.libs.json.Reads[T]

- ambiguous implicit values: both value userReads in object JsonTest of type => play.api.libs.json.Reads[User] and object IntReads in trait DefaultReads of 

type play.api.libs.json.Reads.IntReads.type match expected type play.api.libs.json.Reads[T]

- diverging implicit expansion for type play.api.libs.json.Reads[T] starting with method ArrayReads in trait DefaultReads

- not enough arguments for method fromJson: (implicit fjs: play.api.libs.json.Reads[T])play.api.libs.json.JsResult[T]. Unspecified value parameter fjs.

- diverging implicit expansion for type play.api.libs.json.Reads[T] starting with method ArrayReads in trait DefaultReads

- not enough arguments for method fromJson: (implicit fjs: play.api.libs.json.Reads[T])play.api.libs.json.JsResult[T]. Unspecified value parameter fjs.

Here is the Worksheet using only the import of Json:

import play.api.libs.json.Json

object json {

  case class User(name: String, age: Int, active: Boolean)

  implicit val userReads = Json.reads[User]       //> userReads  : play.api.libs.json.Reads[json.User] = play.api.libs.json.Reads$

                                                  //| $anon$8@144aa0ce

  implicit val userWrites = Json.writes[User]     //> userWrites  : play.api.libs.json.OWrites[json.User] = play.api.libs.json.OWr

                                                  //| ites$$anon$2@5cac6a45

[Daniel Dietrich]

Pascal,

do you think your pull request will make it into Play 2.1-final since it is already tagged as RC1?

[Pascal Voitot Dev]

Actually, you don't need to import Reads._ and Writes._ as those implicits are automatically resolved by Scala compiler as soon as you work with a Reads[A] or a Writes[A].

I'm going to correct this in the samples and tests because this is something I've discovered recently :D

and yes naturally, my pull req will be integrated before final (if other devs find it good :D)
I think a few more optimization in the macro code might still be done...

regards
Pascal

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[Daniel Dietrich]

This all sounds great. I definitely also have to dive into this macro stuff - even if it could result in macro headaches sometimes ;-)

regards

Daniel

[Pascal Voitot Dev]

good luck ;)

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[Daniel Dietrich]

Btw - with the current 2.1-RC1 tag (Utils.scala where added to play.api.libs.functional) my Json example (see above) does not work any more (tried all possible combinations of imports)...

[Pascal Voitot Dev]

if you need to use functional syntax implicits to use combinators to write your own Reads[T] (not generated by macros) using operator "and" for ex, you must import play.api.libs.functional.syntax._ since yesterday!

Pascal

On Sat, Nov 17, 2012 at 1:31 AM, Daniel Dietrich <cafe...@googlemail.com> wrote:

Btw - with the current 2.1-RC1 tag (Utils.scala where added to play.api.libs.functional) my Json example (see above) does not work any more (tried all possible combinations of imports)...

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[Daniel Dietrich]

yes, but I don't use the internal dsl / combinators. It's just reading / writing a case class without additional magic.

For completeness here is the code with corresponding exceptions - but please don't investigate further - the pull request is already in the pipeline...

regards

Daniel

import play.api.libs.json._

import play.api.libs.json.util._

import play.api.libs.json.Reads._

import play.api.libs.json.Writes._

case class User(name: String, age: Int, active: Boolean)

object JsonTest extends App {

  /* value and is not a member of play.api.libs.json.Reads[String]

   * Note: implicit value userReads is not applicable here because it comes

   *       after the application point and it lacks an explicit result type

   */

  implicit val userReads = Json.reads[User]

  

  /*

   * value and is not a member of play.api.libs.json.OWrites[String]

   * Note: implicit value userWrites is not applicable here because it comes

   *       after the application point and it lacks an explicit result type

   */

  implicit val userWrites = Json.writes[User]

  val daniel = User("daniel", 37, true)

  

  /*

   * Multiple markers at this line

   * - No Json deserializer found for type User. Try to implement an implicit Writes or Format for this type.

   * - not enough arguments for method toJson: (implicit tjs: play.api.libs.json.Writes[User])play.api.libs.json.JsValue.

   *   Unspecified value parameter tjs.

   * - No Json deserializer found for type User. Try to implement an implicit Writes or Format for this type.

   * - not enough arguments for method toJson: (implicit tjs: play.api.libs.json.Writes[User])play.api.libs.json.JsValue.

   *   Unspecified value parameter tjs.

   */

  val userJson = Json.toJson(daniel)

  val user = Json.fromJson(userJson)

  println(user.get == daniel)

}

[Pascal Voitot Dev]

you shouldn't import those 4:

import play.api.libs.json._

import play.api.libs.json.util._

import play.api.libs.json.Reads._

import play.api.libs.json.Writes._

but just: (only because you use macros)

import play.api.libs.json.Json

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[Daniel Dietrich]

argh - ok got it. it works with these imports (as expected) -  thx

import play.api.libs.functional.syntax._

import play.api.libs.json._

[Pascal Voitot Dev]

but why do you need Writes._ and even functional.syntax._?
Seeing the code sample, this shouldn't be mandatory.
Don't worry if no answer, it's time to sleep it's very late here ;)

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[Daniel Dietrich]

yes, I got some sleep, too - we live in the same timezone :)

I'm now on the Play20-master branch again (my 'golden source'). Here are the additional imports are needed...

[Daniel Dietrich]

[a little bit off topic]

Pascal,

I'm working on a generic DAO abstraction layer for Slick w/ Play and took the chance to create my first Scala macro :)

Unfortunately I'm stuck at 99,9% of the macro, where a method with a named parameter has to be called via macro.

If you are interested:

http://stackoverflow.com/questions/13446528/howto-model-named-parameters-in-method-invocations-with-scala-macros

Regards

- Daniel

On Saturday, November 17, 2012 1:09:45 AM UTC+1, Pascal wrote:

good luck ;)

 

[Pascal Voitot Dev]

I'll think about it... instead of using copy, you could also try to use constructor directly in the macro...

But just one point: be really careful when you choose macro instead of a classic language pattern. I really consider macro as a tool but not as a patch to solve problems that shouldn't be solved in this way... (I don't say your choice is bad, just to consider macros very precisely ;) )

regards
Pascal

 

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[Daniel Dietrich]

Thank you. It was very interesting to investigate the new Scala macros & reflection features. I see also the pros/cons of changing the default behavior of the compiler - and with that the semantics of the Scala language. One important thing of Scala is its conciseness. With macros things can be done even more concise. That was also my driver in this case. I'm curious if folks will create a Scala_A, Scala_B, ... in the near future - à la 'pimp my language'...

 

greets

Daniel

 

[Jay]

I'm having issues with using the new json libs.  I wrote the following spec

import play.api.test._
import play.api.test.Helpers._
import play.api.libs.json.Json

import models._
import json.JsonFormats._

class JsonFormatsSpec extends Specification {
 
  "JsonFormats" should {
   
    "equals the user jay" in {
      val profile = Profile("Jay Cain")
     
      val settings = Settings()
     
      val jay = User("cain...@gmail.com", profile, settings, "hash", None, false)
     
      val userJson = Json.toJson(jay)  
     
      val user = Json.fromJson(userJson)
      ...
    }
   
  }
}

when I run the test I get the following error:

[error] /Users/cainj/sandbox/pong/test/json/ApplicationSpec.scala:30: diverging implicit expansion for type play.api.libs.json.Reads[T]
[error] starting with method ArrayReads in trait DefaultReads
[error]       val user = Json.fromJson(userJson)
[error]                               ^


Any insight would be helpful.  I'm tried the play master and play-2.1-RC-1

Thx,

Jay

[Jay]

I just looked at the quote above more closely, I need to clone  git://github.com/mandubian/Play20.git

[Daniel Dietrich]

Hi Jay,

it should work with the 2.1 master / rc1 too. Just add these imports and to implicit val's:

Anyway, as of this discussion the json stuff is currently subject of refactoring...

import play.api.libs.json._
import play.api.libs.json.util._

// import play.api.libs.json.Reads._
import play.api.libs.json.Writes._

implicit val userReads = Json.reads[User]

implicit val userWrites = Json.writes[User]

There's a pending pull request which reduces the imports to the minimum...

- Daniel

[Pascal Voitot Dev]

Please try this

import play.api.libs.functional.syntax._

instead of

import play.api.libs.json.util._

(the package has been moved just before releasing RC1)
(FYI in master this import is no more required as well as Writes._)

regards
Pascal

On Mon, Nov 26, 2012 at 5:27 PM, Cristi Boariu <cristi...@gmail.com> wrote:

Hi Daniel,

I used your latest imports (whithout Read) but I receive the same warnings similar to you, my code is:

import play.api.libs.json._

import play.api.libs.json.util._

import play.api.libs.json.Writes._

object AddressBean extends Controller with RestTrait {

  implicit val addressWrites = Json.writes[Address]

  implicit val addressReads = Json.reads[Address]
}

warning: value and is not a member of play.api.libs.json.Reads[Option[Int]] Note: implicit value addressReads is not 

 applicable here because it comes after the application point and it lacks an explicit result type

I'm wondering if you have added anything else to fix these...

Basically I have to make this JSON stuff to work with 2.1-RC1 because my project uses scala 2.10 so can't go back to 2.09... Is there any chance to solve this issue?

Thanks!

--
 
 

[Cristi Boariu]

Wow, it works, thanks.......

[Thibault]

I'm getting a compiler error when the case class has a companion object. I use scala 2.10.0-RC3 and the very latest Play20, built from master branch.

Here is a quick gist to reproduce the problem: https://gist.github.com/4177343

Excellent job with Play 2.1, thanks a bunch! I'm now rewritting http://lichess.org with all that new goodness, it's a lot of fun.

[Thibault]

Interrestingly enouth, I get the same error when I do the mapping manually, without using the macro magic! See that gist https://gist.github.com/4177529

I'm sure there is a better solution than renaming all my companion objects ;) But what could it be?

[Pascal Voitot Dev]

Hi
Did you have same for problem with Scala 2.10RC2 ?

Pascal

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[Pascal Voitot Dev]

If you use Foo.apply, it should work.

As soon as you create object for case class, case class hidden features are overriden by compiler...
Concerning the macro, I think we could improve it a bit and go around this problem.

Pascal

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[Thibault]

Indeed manual mapping with (Foo.apply _) is working.

I tried the macro style with scala 2.10.0-RC2, and no difference, I get the same compiler error.

[Thibault]

No it's the same thing with several attributes. Sorry for the delay, I'm travelling at the moment.

On Sunday, December 2, 2012 12:35:59 AM UTC+1, Grégory Bougeard wrote:

As @mandubian told me, there is a limitation on case class containing one and only one attribute.

Maybe this is your case...

[deVIAntCoDE]

Yes I have the same problem as well. I have had to rename my companion objects as well. What is the progress on the issue though?

I found this ticket relating to it but no comment on it so far.

https://play.lighthouseapp.com/projects/82401/tickets/887-adding-a-companion-object-prevents-json-inception-from-working

[Pascal Voitot Dev]

I haven't tested with latest scala 2.10.0 but it might be a problem in Scala directly...

pascal

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