updating Json object - json

Question

I have a json object that I need to update. The original object is a list that looks like this:
[
{
"firstName":"Jane",
"lastName":"Smith"
},
{
"firstName":"Jack",
"lastName":"Brown"
}
]
For each element in the list, we have an extra field, "age", that needs to be added at run-time, so the result should look like the following:
[
{
"firstName":"Jane",
"lastName":"Smith",
"age": "21"
},
{
"firstName":"Jack",
"lastName":"Brown",
"age": "34"
}
]
Any suggestions how to do this so the result is still json?
Thanks.

Answer 1

request.body.asJson.map {
jm => (jm.as[JsObject] ++ Json.obj("age" -> 123))
}

Answer 2

I would recommended deserializing the JSON array you receive into a List of case classes, then having some function fill in the missing attributes based on the current attributes of the case class, and finally serializing them as JSON and serving the response.
Let's make a Person case class with the fields that will be missing as Option:
import play.api.libs.json.Json
case class Person(firstName: String, lastName: String, age: Option[Int])
object Person {
implicit val format: Format[Person] = Json.format[Person]
def addAge(person: Person): Person = {
val age = ... // however you determine the age
person.copy(age = Some(age))
}
}
Within the companion object for Person I've also defined a JSON serializer/deserializer using the format macro, and a stub for a function that will find a person's age then copy it back into the person and return it.
Deep within the web service call you might then have something like this:
val jsArray = ... // The JsValue from somewhere
jsArray.validate[List[Person]].fold(
// Handle the case for invalid incoming JSON
error => InternalServerError("Received invalid JSON response from remote service."),
// Handle a deserialized array of List[Person]
people => {
Ok(
// Serialize as JSON, requires the implicit `format` defined earlier.
Json.toJson(
// Map each Person to themselves, adding the age
people.map(person => Person.addAge(person))
)
)
}
)
This method is much safer, otherwise you'll have to extract values from the array one by one and concatenate objects, which is very awkward. This will also allow you to easily handle errors when the JSON you receive is missing fields you're expecting.