spray-json - List of case class property

[Gregg Carrier]

I'm sure I'm missing something basic but I can't figure it out. I have
two case classes like this:

case class Foo(x: String, y: List[Bar])
case class Bar(z: Long)

then I have two formats like this:

object FooJsonProtocol extends DefaultJsonProtocol {
implicit val fooFormat = jsonFormat(Foo, "x", "y")
}

object BarJsonProtocol extends DefaultJsonProtocol {
implicit val barFormat = jsonFormat(Bar, "z")
}

I import them into scope like:

import FooJsonProtocol.fooFormat
import BarJsonProtocol.barFormat

But I get a compile error:

could not find implicit value for evidence parameter of type
FooJsonProtocol.JF[List[Bar]]

What am I missing? Thanks!

Gregg

[elbowich]

Did you bring List format implicit into scope?

[Saku]

Try using simply

import FooJsonProtocol._

it will import the List format from DefaultJsonProtocol as its what
your FooJsonProtocol extends

[Mathias]

Gregg,

as Saku already pointed out you need to bring the whole protocol into scope, not only the JsonFormat(s) for your class(es).
Also, you don't need to create separate protocol objects for each case class.
It's enough if you create one custom object and import all of its members:

object MyJsonProtocol extends DefaultJsonProtocol {

implicit val fooFormat = jsonFormat(Foo, "x", "y")

implicit val barFormat = jsonFormat(Bar, "z")
}

import MyJsonProtocol._

Cheers,
Mathias

---
mat...@spray.cc
http://www.spray.cc

[Gregg Carrier]

Thanks for the tips. I now have:

import MyJsonProtocol._

I am still getting the error I mentioned above, but I am also getting
an ambiguous implicit error - that's actually why I explicitly
imported my formatters in the first place.

ambiguous implicit values:
[error] both value StringMarshaller in trait DefaultMarshallers of
type => cc.spray.typeconversion.MarshallerBase[String]
[error] and method sprayJsonMarshaller in trait SprayJsonSupport of
type [A](implicit evidence$2:
cc.spray.json.JsonWriter[A])cc.spray.typeconversion.MarshallerBase[A]{lazy
val printer: cc.spray.json.JsonPrinter}
[error] match expected type cc.spray.http.ContentType =>
Option[cc.spray.http.ContentType] =>
cc.spray.typeconversion.Marshalling[String]
[error] ctx.fail(400, "user %s already
exists".format(u.get("_id")))

Is there a good way to deal with that one? Thanks for the help.

[Mathias]

Gregg,

ok, two more things you need to change:

1. To fix the "could not find implicit value" error you need to switch the declaration order in your MyJsonProtocol:

object MyJsonProtocol extends DefaultJsonProtocol {

implicit val barFormat = jsonFormat(Bar, "z")
implicit val fooFormat = jsonFormat(Foo, "x", "y")
}

2. To fix the "ambiguous implicit values" error you could switch to the latest snapshots of spray-server and spray-json or manually remove the ambiguity, e.g. by using an "import SprayJsonSupport._" (rather then mixing in the SprayJsonSupport trait) at a scope that doesn't include the `ctx.fail` line or by explicitly specifying the marshaller to be used:

ctx.fail(400, "user %s already exists".format(u.get("_id")))(StringMarshaller)

HTH and cheers,
Mathias

---
mat...@spray.cc
http://www.spray.cc

[Kane Kim]

Hello Mathias,

So, it's easy to unmarshal json object:

      case class Foo(name: List[Int])

      object MyJsonProtocol extends DefaultJsonProtocol {

        implicit val i = jsonFormat1(Foo)

      }

      import MyJsonProtocol._

What if i want to unmarshal a list? I've found it's even easier to do it explicitly: val args = request.asJson.convertTo[List[Int]], but what is the idiomatic way to do this?

Thanks!

[Mathias Doenitz]

Kane,

> What if i want to unmarshal a list? I've found it's even easier to do it
> explicitly: val args = request.asJson.convertTo[List[Int]], but what is the
> idiomatic way to do this?

if all you have on the JSON side really is only an array of numbers then your code should be good enough.

Cheers,
Mathias

---
mat...@spray.io
http://spray.io

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[Sudeep Reddy Gaddam]

Hi Mathias,

What if I have Set[String] instead of List? How to handle marshalling/Unmarshalling??

case class User (
    .....
    friendsLists : Set[String])

object UserJsonSupport extends DefaultJsonProtocol with SprayJsonSupport {

  implicit val UserFormat = jsonFormat12(UserService.User)
}

Error:(39, 43) could not find implicit value for evidence parameter of type UserJsonSupport.JF[scala.collection.mutable.Set[String]]
    implicit val UserFormat = jsonFormat12(UserService.User)
                                          ^

How to deal with such cases?

[Age Mooij]

FYI DefaultJsonProtocol only supports  immutable Sets, Seqs, Vectors, etc. It seems you are trying to marshal a mutable set and that is not supported. 

The implementations are in https://github.com/spray/spray-json/blob/master/src/main/scala/spray/json/CollectionFormats.scala

If you absolutely have to use mutable collections, you can most copy the immutable implementations and adjust them to fit your needs.

Hope this helps

Age

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