Lift JSON LINQ Like Dynamic Extraction Pattern

Question

I am attempting to perform an XPath based extraction using Lift JSON except that the xpath pattern of extraction is determined during runtime

To illustrate, I'd like to convert string "a.b.c.d" to Lift JSON extraction using (json \ "a" \ "b" \ "c").extract[List[Int]]

import net.liftweb.json._
import net.liftweb.json.JsonDSL._
import net.liftweb.json.JsonAST._
import net.liftweb.json.Extraction._
implicit val formats = net.liftweb.json.DefaultFormats

val x = """{ "a" : { "b" : [ {"c" : 10},{ "c" : 20 } ] } }""" 
val json = parse(x)

val dataString = "a.b.c"

val dataList = dataString.split("\\.").toList
// List(a,b,c)

// I'd want to convert the above string to - (json \ "a" \ "b" \ "c").extract[List[Int]]

Is it possible to use foldLeft to achieve this pattern?

score 1 · Accepted Answer · answered Mar 15 '13 at 11:37

If I understand your question, this is what you want:

List("a", "b", "c").foldLeft(json){ _ \ _ }.extract[List[Int]]

And to help understand why: foldLeft takes two arguments; an initial state, and a function that takes the "current" state and the next input, returning the "next" state. The "inputs" are the elements of the thing you're calling foldLeft on, i.e. the List("a", "b", "c").

So if you use json as your initial state, the first state change call will be json \ "a". The next will be the result of that calculation, backslash "b", and so on.

Lift JSON LINQ Like Dynamic Extraction Pattern

1 Answers1