Best practice to create a JSON string of one object containing an array of other objects using Ruby?

Question

What is a good practice to create a JSON string of one object (object of class A) containing an array of objects (objects of class B)? I am particularly interessted in the implementation of class's A to_json method.

Assuming class A looks as follows:

class A
  attr_accessor :items
  def initialize()
    @items = Array.new
  end
  def to_json(*a)
    ?SECRET OF THE DAY?
  end
end

and class B:

class B
  def to_json(*a)
    {"class B" => "class B"}.to_json(*a)
  end
end

The best solution I got so far is:

def to_json(*a)
  json = Array.new
  @items.each do |item|
    json << item.to_json(*a)
  end
  {"class A" => json}.to_json(*a)
end

Assuming there is only one item in array of an object of class A, the resulting JSON string looks as follows:

{"class A":["{\"class B\":\"class B\"}"]}

I am sure we can do better?

hrnt · Accepted Answer · 2011-02-09 11:38:21Z

1

I would do this instead

 def to_json(*a)
      {"class A" => @items}.to_json(*a)
 end

The problem with your approach is that your @items array contains strings, not objects. In that case your to_json will create an array of strings, not an array of objects.

answered Feb 9, 2011 at 11:38

hrnt

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1 Comment

Scholle Over a year ago

I have tried this before, it results in IOError exception in class A, saying to_json "not opened for reading"...

Scholle · Accepted Answer · 2011-02-09 21:48:22Z

1

Reinstalling/upgrading json/json_pure to 1.5.1 finally solved the IOError exception issue.

Using: Rails 3.0.3 ruby 1.9.2p136 (2010-12-25 revision 30365) [i386-darwin9.8.0] json 1.5.1 json_pure 1.5.1

Refer to http://www.ruby-forum.com/topic/1052511#new for further guidance...

answered Feb 9, 2011 at 21:48

Scholle

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