how to represent nested JSON object in a case class using Json4s?

Question

Given an example JSON object with a nested object who's properties are unkown:

      { "Key":"01234",
          "eventProperties":{
             "unknownProperty1":"value",
             "unknownProperty2":"value",
             "unknownProperty3":"value"
          },
       }

I have tried to use json4s' extract function with the following case class (In Scala):

case class nestedClass(Key:String, eventProperties:Map[(String,Any)])

Which results in the following error:

org.json4s.package$MappingException: Can't find constructor for nestedClass

Is it possible to do this without defining every possible property of eventProperties?

Update: there was a bug in json4s 3.2.10 causing this issue - updating to 3.2.11 and extracting to Map[String,Any] works fine.

Tim · Accepted Answer · 2015-09-01 18:48:53Z

2

I'm not sure what you are doing to get the exception you have posted, but the following works (note a Map instead of List):

import org.json4s._
import org.json4s.jackson.JsonMethods._
import org.json4s.DefaultFormats

val json = parse("""
{ "key":"01234",
  "eventProperties":{
    "unknownProperty1":"value",
    "unknownProperty2":"value",
    "unknownProperty3":"value"
  }
}
""")

case class NestedClass(key:String, eventProperties:Map[String,Any])

implicit val formats = DefaultFormats

json.extract[NestedClass]

answered Sep 1, 2015 at 18:48

Tim

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3 Comments

Gillespie Over a year ago

Thanks, but using this I get: scala> org.json4s.package$MappingException: No usable value for eventProperties No information known about type

Gillespie Over a year ago

Turns out there's a bug in 3.2.10 that's the problem - 3.2.11 fixed it

Tim Over a year ago

if you plan to serialize more complicated stuff, I suggest using Jackson + Scala plugin for serialization/deserialization. Last time I checked it was supporting a larger subset of Scala constructs than json4s. json4s using Jackson internally anyways.

S.Karthik · Accepted Answer · 2015-09-02 07:59:23Z

0

In Order to get eventProperties as List[(String, Any)], your json should be,

         """ {
               "key": "01234",
               "eventProperties": [
                   {"unknownProperty1": "value"},
                   {"unknownProperty2": "value"},
                   {"unknownProperty3": "value"}
               ]
           }"""

Otherwise, you can use Map instead of List as case class nestedClass1(key:String, eventProperties:Map[String,Any]) and then convert to nestedClass as nestedClass( n1.key, n1.eventProperties.toList)

edited Sep 2, 2015 at 7:59

answered Sep 2, 2015 at 7:41

S.Karthik

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