Lua

JSON Paths

See more JSON Examples

Demonstrates using "Chilkat JSON Paths" to access parts of a JSON document, or to iterate over parts.

This example uses the following JSON document:

{
    "nestedArray" : [
			[
				[1,2,3],
				[4,5,6],
				[7,8,9,10]
			],
			[
				[11,12,13],
				[14,15,16],
				[17,18,19,20]
			],
			[
				[21,22,23],
				[24,25,26],
				[27,28,29,30],
				[31,32,33,34,35,36]
			]
		],

	"nestedObject" : {
		"aaa" : {
			"bb1" : {
				"cc1" : "c1Value",
				"cc2" : "c2Value",
				"cc3" : "c3Value"
			},
			"bb2" : {
				"dd1" : "d1Value",
				"dd2" : "d2Value",
				"dd3" : "d3Value"
			}
		}
	},

	"mixture" : {
		"arrayA" : [  
			{ "fruit": "apple", "animal": "horse", "job": "fireman", "colors": ["red","blue","green"] },
			{ "fruit": "pear", "animal": "plankton", "job": "waiter", "colors": ["yellow","orange","purple"] },
			{ "fruit": "kiwi", "animal": "echidna", "job": "astronaut", "colors": ["magenta","tan","pink"] }
			]
	},


        "name.with.dots" : { "grain" : "oats" }

	
}

Lua

local chilkat = require("chilkat")

local json = chilkat.JsonObject.new()
json.emit_compact = false

-- Assume the file contains the data as shown above..
local success = json:load_file("qa_data/json/pathSample.json")
if not success then
    print(json.last_error_text)
    return
end

-- First, let's get the value of "cc1"
-- The path to this value is: nestedObject.aaa.bb1.cc1
print(json:string_of("nestedObject.aaa.bb1.cc1"))

-- Now let's get number 18 from the nestedArray.
-- It is located at nestedArray[1][2][1]
-- (remember: Indexing is 0-based)
print("This should be 18: " .. json:int_of("nestedArray[1][2][1]"))

-- We can do the same thing in a more roundabout way using the
-- I, J, and K properties.  (The I,J,K properties will be convenient
-- for iterating over arrays, as we'll see later.)
json.i = 1
json.j = 2
json.k = 1
print("This should be 18: " .. json:int_of("nestedArray[i][j][k]"))

-- Let's iterate over the array containing the numbers 17, 18, 19, 20.
-- First, use the SizeOfArray method to get the array size:
local sz = json:size_of_array("nestedArray[1][2]")
-- The size should be 4.
print("size of array = " .. sz .. " (should equal 4)")

-- Now iterate...
for i = 0, sz - 1 do
    json.i = i
    print(json:int_of("nestedArray[1][2][i]"))
end

-- Let's use a triple-nested loop to iterate over the nestedArray:

-- szI should equal 1.
local szI = json:size_of_array("nestedArray")
for i = 0, szI - 1 do
    json.i = i

    local szJ = json:size_of_array("nestedArray[i]")
    for j = 0, szJ - 1 do
        json.j = j

        local szK = json:size_of_array("nestedArray[i][j]")
        for k = 0, szK - 1 do
            json.k = k

            print(json:int_of("nestedArray[i][j][k]"))
        end
    end
end

-- Now let's examine how to navigate to JSON objects contained within JSON arrays.
-- This line of code gets the value "kiwi" contained within "mixture"
print(json:string_of("mixture.arrayA[2].fruit"))

-- This line of code gets the color "yellow"
print(json:string_of("mixture.arrayA[1].colors[0]"))

-- Getting an object at a path:
-- This gets the 2nd object in "arrayA"

local obj2 = chilkat.JsonObject.new()
json:object_of2("mixture.arrayA[1]", obj2)

-- This object's "animal" should be "plankton"
print(obj2:string_of("animal"))

-- Note that paths are relative to the object, not the absolute root of the JSON document.
-- Starting from obj2, "purple" is at "colors[2]"
print(obj2:string_of("colors[2]"))

-- Getting an array at a path:
-- This gets the array containing the colors red, green, blue:

local arr1 = chilkat.JsonArray.new()
json:array_of2("mixture.arrayA[0].colors", arr1)

local szArr1 = arr1.size
for i = 0, szArr1 - 1 do
    print(i .. ": " .. arr1:string_at(i))
end

-- The Chilkat JSON path uses ".", "[", and "]" chars for separators.  When a name
-- contains one of these chars, use double-quotes in the path:
print(json:string_of("\"name.with.dots\".grain"))