Converting a custom object into JSON using JSON gem

Question

I am learning how to parse and generate JSON with the JSON gem. I am easily able to create a hash of data and generate that into JSON; however, I am having a brain fart when it comes to taking a instance of a class (such as a Person instance) and putting all of its instance variables inside a hash to be converted into JSON.

This is the example I am having trouble with:

require "json"

class Person

  def initialize(name, age, address)
    @name = name
    @age = age
    @address = address
  end

  def to_json

  end


end

p = Person.new('John Doe', 46, "123 Elm Street")
p.to_json

I want to create a .to_json method so that I can take a person object and have all of its instance variables converted into JSON. What I think I need to do is take all of the Person's instance variables, put them in a hash then call JSON.generate(hash). I am having a brain fart on how to do that right now. So can someone help me complete the to_json method, or perhaps suggest a better way of implementing it? Thanks!

Answer 1

First you need to make sure you use the right basic structure:

def to_json(*a)
  {
    'json_class'   => self.class.name,
    'data'         => Your data
  }.to_json(*a)
end

The json_class key is used by the JSON gem to determine what class to pass the data to. The *a parameter includes all the arguments that the JSON gem is passing in, generally unimportant for your classes so you just pass it straight on to the hash's to_json call. Next the simplest ways to store your data are a hash or an array:

    'data'         => [@name, @age, @address]

or

    'data'         => { 'name' => @name, 'age' => @age, 'address' => @address

The first might be faster and makes the self.json_create method slightly easier to write, while the second is a lot easier to make backward compatible if you ever change the data structure and wish to load old JSON objects.