Extract nested JSON element using scala

Question

I have the following code in Scala. My goal is to extract the value(s) of a key without knowing how many and how deep they are.

    import org.json4s.jackson.JsonMethods._

    import org.json4s.{DefaultFormats, JField, JObject, JString, JValue}



    object jsonLift {



        implicit val formats = DefaultFormats



        val js = parse(

            """

    {

      "url": "imap.yahoo.com",

        "credentials": {

        "username": "myusername",

        "password": "mypassword"

         },

        "some key":{

            "other key": {

                "username": "hello"

            }

        }

    }

            """)





            def getElem(elem: String, json:JValue) = for {

                    JObject(child) <- json

                    JField(elem, JString(value)) <- child       // this does not return the expected result

    //              JField("username", JString(value)) <- child // this returns the expected result

                } yield  value





        def main(args: Array[String]) {



            val result = getElem("username", js)

            println(result)



        }

    }

The result of the above code is

List(imap.yahoo.com, myusername, mypassword, hello)

which is not what I am expecting. My expected result is

List(myusername, hello)

.

However, if I change the variable

elem

, directly inside the method

getElem

, with the key (as string) that I am interested in (Eg: "username") I get the expected result:

List(myusername, hello)

which are all the values of the key "username".

How can I get the expected list of value(s) by calling the method

getElem

with the name of the JSON key as argument? Eg:

getElem("JSON key", json)

Thank you!

Answer 1

Change getElem to

def getElem(elem: String, json:JValue) = for {
  JObject(child) <- json
  JField(`elem`, JString(value)) <- child
} yield  value

Without the backticks around elem on the RHS, you are binding the first element of type JField = (String, JValue) to a new name elem and shadowing the method parameter elem

Extract nested JSON element using scala

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