case class -> json

[Hugo Gävert]

Hi!

Anybody here? Trying to look into bijection. I'm still trying to understand things. There is bijection from simple types to json. Can this therefore do bijection from case class to json?

Yes, I'm trying to find a way to serialize case classes to json for publishing in scala 2.10. Jerkson was great and simple, but....

-- 

Hugo.

[Sam Ritchie]

Welcome, Hugo! Not much activity yet on the list, but we're absolutely around.

If you can define a Bijection[YourCaseClass, Tuple] then you'll be able to compose it with JsonInjection.toString and be good to go. The required JsonNodeInjection is built up from the primitive ones, as you noticed.

Here's an example:

https://gist.github.com/sritchie/6625178

import com.twitter.bijection._
import com.twitter.bijection.json.JsonInjection
import com.twitter.bijection.json.JsonNodeInjection._ // implicits required for building up JsonInjections from primitives
 
// Here's some custom case class that we'd like to be able to serialize into Json.
case class Wrapper(x: Int, y: Long)
 
// Now, we define a Bijection from our case class to a tuple.
val wrapperToTuple = Bijection.build[Wrapper, (Int, Long)](Wrapper.unapply(_).get)(Wrapper.tupled(_))
 
// Next we'll compose this with the library-supplied injection from Product -> String provided by JsonInjection:
val wrapperToString: Injection[Wrapper,Stri
ng] = wrapperToTuple.andThen(JsonInjection.toString[(Int, Long)])
 
// Forward gets us to string, always:
val json: String = wrapperToString(Wrapper(10, 11L)) // String = [10,11]
 
// Invert returns a try:
wrapperToString.invert(Wrapper(10, 11L)) // scala.util.Try[Wrapper] = Success(Wrapper(10,11))

 

Hugo Gävert

September 19, 2013 1:02 AM

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Sam Ritchie, Twitter Inc
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@sritchie

[Hugo Gävert]

Thanks for the answer!

I was looking at the code and to be honest, I kind of got the feeling that this is what it would do. Except I was looking for the more traditional JSON serialization which would serialize the Wrapper(10, 11L) as {x: 10, y: 11}. Which obviously looses the type information in this case (and is not bijection), but it still is what I'm looking for. Yeah, I wasn't looking for bijection :-)

(I'm currently trying out play-json for writing and in future reading JSONs).

-- 

Hugo.

[Oscar Boykin]

You could do that too with an Injection from Wrapped -> Map[String, JsonNode] -> String

Just a different path than Sam took.

This will be automatic with scala 2.10 as the required base (we can use macros), but for now, you still need to wire it up.

https://gist.github.com/johnynek/6674286

scala> inj2(Wrapped(1, 3L))
res1: String = {"x":1,"y":3}


 
scala> inj2.invert(res1)
res2: scala.util.Try[Wrapped] = Success(Wrapped(1,3))

Oscar Boykin :: @posco :: http://twitter.com/posco