Extracting certain fields from scala object <-> Json - json

Question

I'm trying to extract certain fields from Scala object before converting to Json. Is there an easy way to do this.
It would also work if i could make a new Json with certain fields from a Json.

Answer 1

You can simply extract out the value of a Json and scala gives you the corresponding map. Example:
var myJson = Json.obj(
"customerId" -> "xyz",
"addressId" -> "xyz",
"firstName" -> "xyz",
"lastName" -> "xyz",
"address" -> "xyz"
)
Suppose you have the Json of above type. To convert it into map simply do:
var mapFromJson = myJson.value
This gives you a map of type : scala.collection.immutable.HashMap$HashTrieMap

Answer 2

Hard to say without more details. Suppose that you have the following Scala case class...
case class SomeObject(customerId: Long, addressId: Long, firstName: String, lastName: String, address: String)
...and that you wanted to extract the 'firstName', 'lastName', and address fields and then convert the object to Json. Using play-json you could define an implicit conversion on the companion object for the SomeObject class...
object SomeObject {
implicit val someObjectWrites = new Writes[SomeObject] {
def writes(object: SomeObject) = Json.obj(
"firstName" -> object.firstName,
"lastName" -> object.lastName,
"address" -> object.address
)
}
}
Then you could just use the code as follows:
val obj = SomeObject(12345, 678910, "John", "Doe", "My Address")
val json = Json.toJson(obj)
Note that there are probably other JSON libraries, besides play-json, that support similar functionality.