How can I access the nested values in JsValue? - scala

Question

I have the following Json string
{
"results" : [
{
"address_components" : [
{
"long_name" : "1600",
"short_name" : "1600",
"types" : [ "street_number" ]
},
{
"long_name" : "Amphitheatre Parkway",
"short_name" : "Amphitheatre Pkwy",
"types" : [ "route" ]
},
{
"long_name" : "Mountain View",
"short_name" : "Mountain View",
"types" : [ "locality", "political" ]
}
]}]}
I parse it using the following statement
val payload = Json.parse(results)
I then get the following results
payload: play.api.libs.json.JsValue = {"results":[{"address_components":[{"long_name":"1600","short_name":"1600","types":["street_number"]},{"long_name":"Amphitheatre Parkway","short_name":"Amphitheatre Pkwy","types":["route"]},{"long_name":"Mountain View","short_name":"Mountain View","types":["locality","political"]}]}
When I try and run this command
val extract = (payload \ "results.address_components")
I get the following output
play.api.libs.json.JsLookupResult = JsUndefined('results.address_components' is undefined on object
How do I access the element "address_components" ?

Answer 1

I'd recommend using case classes kind of like GamingFelix's suggestion (an alternative to that is below the line in my answer), but if you're wondering why your example didn't work here's why:
You didn't traverse the array properly. Given the following JSON:
{
"foo": [
{
"bar": 123,
"baz": "abc"
},
{
"bar": 456,
"baz": "def"
}
]
}
you'd get all of the bar values like this: Json.parse(result) \ "foo" \\ "bar" - ie, use double backslashes. You can chain this together too, like (Json.parse(result) \\ "field1").map(_ \\ "field2") etc.
So in your example, if you want all of the long_name fields you'd do it like this:
import play.api.libs.json.Json
val json = Json.parse(
"""{"results" : [{"address_components" : [{"long_name" : "1600","short_name" : "1600","types" : [ "street_number" ]},{"long_name" : "Amphitheatre Parkway","short_name" : "Amphitheatre Pkwy","types" : [ "route" ]},{"long_name" : "Mountain View","short_name" : "Mountain View","types" : [ "locality", "political" ]}]},{"address_components" : [{"long_name" : "16400","short_name" : "1600","types" : [ "street_number" ]},{"long_name" : "Amphitheatre 5Parkway","short_name" : "Amphitheatre Pkwy","types" : [ "route" ]},{"long_name" : "Mounta6in View","short_name" : "Mountain View","types" : [ "locality", "political" ]}]}]}"""
)
(json \ "results" \\ "address_components").map(_ \\ "long_name")
This returns an array of arrays, since you're going through multiple arrays to get your value. If you put a .foreach(_.foreach(println)) on the end, you'll get this:
"1600"
"Amphitheatre Parkway"
"Mountain View"
"16400"
"Amphitheatre 5Parkway"
"Mounta6in View"
See it working on Scastie.
If you're curious, GamingFelix's suggestion to almost combine the two approaches isn't really the best - it's easier to follow what's going on if you just convert the entire thing into case classes instead. Also, if you create a companion object to each case class to put the formatters in, instead of keeping everything in the same formatter object, you won't need to explicitly import formatters every time you need them (Scala will find them automatically).
This is how I'd do it:
import play.api.libs.json.{Json, OFormat}
val json = Json.parse(
"""{"results" : [{"address_components" : [{"long_name" : "1600","short_name" : "1600","types" : [ "street_number" ]},{"long_name" : "Amphitheatre Parkway","short_name" : "Amphitheatre Pkwy","types" : [ "route" ]},{"long_name" : "Mountain View","short_name" : "Mountain View","types" : [ "locality", "political" ]}]},{"address_components" : [{"long_name" : "16400","short_name" : "1600","types" : [ "street_number" ]},{"long_name" : "Amphitheatre 5Parkway","short_name" : "Amphitheatre Pkwy","types" : [ "route" ]},{"long_name" : "Mounta6in View","short_name" : "Mountain View","types" : [ "locality", "political" ]}]}]}"""
)
case class MyClass(results: Seq[Result])
object MyClass {
implicit val format: OFormat[MyClass] = Json.format[MyClass]
}
case class Result(address_components: Seq[AddressComponent])
object Result {
implicit val format: OFormat[Result] = Json.format[Result]
}
case class AddressComponent(long_name: String, short_name: String, types: Seq[String])
object AddressComponent {
implicit val format: OFormat[AddressComponent] = Json.format[AddressComponent]
}
val model = json.as[MyClass] // `.as` is unsafe, use `.asOpt` or `.validate` or something like that in a real scenario
model.results.flatMap(_.address_components.map(_.long_name)) // get values out like you normally would in a class
Here's that working on Scastie.

Answer 2

So since you're using play api, you can use implicits and case classes.
I usually use this website: https://json2caseclass.cleverapps.io/
to turn the json into scala case classes. And then I create implicits for the case classes.
Here's how I do it:
import play.api.libs.json._
case class Address_components(
long_name: String,
short_name: String,
types: List[String]
)
case class Results(
address_components: List[Address_components]
)
case class RootJsonObject(
results: List[Results]
)
implicit val a: Format[Address_components] = Json.format[Address_components]
implicit val b: Format[Results] = Json.format[Results]
implicit val c: Format[RootJsonObject] = Json.format[RootJsonObject]
Then you can easily parse the json and access them.
val test = Json.parse("""{
"results" : [
{
"address_components" : [
{
"long_name" : "1600",
"short_name" : "1600",
"types" : [ "street_number" ]
},
{
"long_name" : "Amphitheatre Parkway",
"short_name" : "Amphitheatre Pkwy",
"types" : [ "route" ]
},
{
"long_name" : "Mountain View",
"short_name" : "Mountain View",
"types" : [ "locality", "political" ]
}
]}]}""")
println(test.validate[RootJsonObject])
val mylist = (test \ "results").get.as[List[Results]]
mylist.map(a => println(a))
I also created a Scalafiddle for you if you wanna test it out in the browser:
https://scalafiddle.io/sf/J5dDfFo/6