From: Brian Candler <b.candler@...>
Date: 2011-02-10T04:07:17+09:00
Subject: Re: Best practice to create a JSON string of one object containing an array of other objects using R

> But it results in IOError exception in class A, saying to_json "not
> opened for reading"...
>
> I am sure we can do better?

I think it would be much better to make the class an attribute of the 
JSON object, not build a new JSON object of {class => {attributes}}

If you look at the tests/ directory of the json or json_pure gem, you'll 
see that they use 'json_class' for this purpose. e.g.

  class A
    def initialize(a)
      @a = a
    end

    attr_reader :a

    def ==(other)
      a == other.a
    end

    def self.json_create(object)
      new(*object['args'])
    end

    def to_json(*args)
      {
        'json_class'  => self.class.name,
        'args'        => [ @a ],
      }.to_json(*args)
    end
  end

The use of the 'args' element (being the array of arguments to #new) is 
fairly ugly. I would rather expose the instance variables as members of 
the JSON object:

  class A
    def initialize(a)
      @a = a
    end

    attr_reader :a

    def self.json_create(object)
      new(object['a'])
    end

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

  a1 = A.new([123, 456])
  puts a1.inspect
  str = a1.to_json
  puts str
  a2 = JSON.parse(str)
  puts a2.inspect

HTH,

Brian.

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