Jbuilder

Jbuilder gives you a simple DSL for declaring JSON structures that beats massaging giant hash structures. This is particularly helpful when the generation process is fraught with conditionals and loops. Here's a simple example:

Jbuilder.encode do |json|
  json.content format_content(@message.content)
  json.(@message, :created_at, :updated_at)

  json.author do |json|
    json.name @message.creator.name.familiar
    json.email_address @message.creator.email_address_with_name
    json.url url_for(@message.creator, format: :json)
  end

  if current_user.admin?
    json.visitors calculate_visitors(@message)
  end

  json.comments @message.comments, :content, :created_at
  
  json.attachments @message.attachments do |json, attachment|
    json.filename attachment.filename
    json.url url_for(attachment)
  end
end

This will build the following structure:

{ 
  "content": "<p>This is <i>serious</i> monkey business",
  "created_at": "2011-10-29T20:45:28-05:00",
  "updated_at": "2011-10-29T20:45:28-05:00",

  "author": {
    "name": "David H.",
    "email_address": "'David Heinemeier Hansson' <david@heinemeierhansson.com>",
    "url": "http://example.com/users/1-david.json"
  },

  "visitors": 15,

  "comments": [
    { "content": "Hello everyone!", "created_at": "2011-10-29T20:45:28-05:00" },
    { "content": "To you my good sir!", "created_at": "2011-10-29T20:47:28-05:00" }
  ],
  
  "attachment": [
    { "filename": "forecast.xls", "url": "http://example.com/downloads/forecast.xls" },
    { "filename": "presentation.pdf", "url": "http://example.com/downloads/presentation.pdf" }
  ]
}

You can either use Jbuilder stand-alone or directly as an ActionView template language. When required in Rails, you can create views ala show.json.jbuilder (the json is already yielded):

# Any helpers available to views are available to the builder
json.content format_content(@message.content)
json.(@message, :created_at, :updated_at)

json.author do |json|
  json.name @message.creator.name.familiar
  json.email_address @message.creator.email_address_with_name
  json.url url_for(@message.creator, format: :json)
end

if current_user.admin?
  json.visitors calculate_visitors(@message)
end

# You can use partials as well, just remember to pass in the json instance
json.partial! "api/comments/comments", @message.comments

Libraries similar to this in some form or another includes:

• RABL: https://github.com/nesquena/rabl
• JsonBuilder: https://github.com/nov/jsonbuilder
• JSON Builder: https://github.com/dewski/json_builder
• Jsonify: https://github.com/bsiggelkow/jsonify
• RepresentationView: https://github.com/mdub/representative_view

Compatibility Notes

Jbuilder works best with Ruby 1.9. It does not work so well with Ruby 1.8.

Jbuilder leverages "block local variables" found in Ruby 1.9. So when you write code like:

json.author do |json|
  # notice json variable in here
  json.name @message.creator.name.familiar
end

The issue is that the "inner" json in the block overwrites the parent and causes strange looking issues to appear.