Jbuilder
Jbuilder gives you a simple DSL for declaring JSON structures that beats manipulating giant hash structures. This is particularly helpful when the generation process is fraught with conditionals and loops. Here's a simple example:
# app/views/messages/show.json.jbuilder
json.content format_content(@message.content)
json.(@message, :created_at, :updated_at)
json.author do
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 |attachment|
json.filename attachment.filename
json.url url_for(attachment)
end
This will build the following structure:
{
"content": "<p>This is <i>serious</i> monkey business</p>",
"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" }
],
"attachments": [
{ "filename": "forecast.xls", "url": "http://example.com/downloads/forecast.xls" },
{ "filename": "presentation.pdf", "url": "http://example.com/downloads/presentation.pdf" }
]
}
To define attribute and structure names dynamically, use the set!
method:
json.set! :author do
json.set! :name, 'David'
end
# => {"author": { "name": "David" }}
To merge existing hash or array to current context:
hash = { author: { name: "David" } }
json.post do
json.title "Merge HOWTO"
json.merge! hash
end
# => "post": { "title": "Merge HOWTO", "author": { "name": "David" } }
Top level arrays can be handled directly. Useful for index and other collection actions.
# @comments = @post.comments
json.array! @comments do |comment|
next if comment.marked_as_spam_by?(current_user)
json.body comment.body
json.author do
json.first_name comment.author.first_name
json.last_name comment.author.last_name
end
end
# => [ { "body": "great post...", "author": { "first_name": "Joe", "last_name": "Bloe" }} ]
You can also extract attributes from array directly.
# @people = People.all
json.array! @people, :id, :name
# => [ { "id": 1, "name": "David" }, { "id": 2, "name": "Jamie" } ]
Jbuilder objects can be directly nested inside each other. Useful for composing objects.
class Person
# ... Class Definition ... #
def to_builder
Jbuilder.new do |person|
person.(self, :name, :age)
end
end
end
class Company
# ... Class Definition ... #
def to_builder
Jbuilder.new do |company|
company.name name
company.president president.to_builder
end
end
end
company = Company.new('Doodle Corp', Person.new('John Stobs', 58))
company.to_builder.target!
# => {"name":"Doodle Corp","president":{"name":"John Stobs","age":58}}
You can either use Jbuilder stand-alone or directly as an ActionView template language. When required in Rails, you can create views a la 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.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. The following will render the file
views/comments/_comments.json.jbuilder
, and set a local variable
comments
with all this message's comments, which you can use inside
the partial.
json.partial! 'comments/comments', comments: @message.comments
It's also possible to render collections of partials:
json.array! @posts, partial: 'posts/post', as: :post
# or
json.partial! 'posts/post', collection: @posts, as: :post
# or
json.partial! partial: 'posts/post', collection: @posts, as: :post
# or
json.comments @post.comments, partial: 'comments/comment', as: :comment
You can pass any objects into partial templates with or without :locals
option.
json.partial! 'sub_template', locals: { user: user }
# or
json.partial! 'sub_template', user: user
You can explicitly make Jbuilder object return null if you want:
json.extract! @post, :id, :title, :content, :published_at
json.author do
if @post.anonymous?
json.null! # or json.nil!
else
json.first_name @post.author_first_name
json.last_name @post.author_last_name
end
end
To prevent Jbuilder from including null values in the output, you can use the ignore_nil!
method:
json.ignore_nil!
json.foo nil
json.bar "bar"
# => { "bar": "bar" }
Fragment caching is supported, it uses Rails.cache
and works like caching in
HTML templates:
json.cache! ['v1', @person], expires_in: 10.minutes do
json.extract! @person, :name, :age
end
You can also conditionally cache a block by using cache_if!
like this:
json.cache_if! !admin?, ['v1', @person], expires_in: 10.minutes do
json.extract! @person, :name, :age
end
If you are rendering fragments for a collection of objects, have a look at
jbuilder_cache_multi
gem. It uses fetch_multi (>= Rails 4.1) to fetch
multiple keys at once.
Keys can be auto formatted using key_format!
, this can be used to convert
keynames from the standard ruby_format to camelCase:
json.key_format! camelize: :lower
json.first_name 'David'
# => { "firstName": "David" }
You can set this globally with the class method key_format
(from inside your
environment.rb for example):
Jbuilder.key_format camelize: :lower
Faster JSON backends
Jbuilder uses MultiJson, which by default will use the JSON gem. That gem is
currently tangled with ActiveSupport's all-Ruby #to_json
implementation,
which is slow (fixed in Rails >= 4.1). For faster Jbuilder rendering, you can
specify something like the Yajl JSON generator instead. You'll need to include
the yajl-ruby
gem in your Gemfile and then set the following configuration
for MultiJson:
require 'multi_json'
MultiJson.use :yajl
Contributing to Jbuilder
Jbuilder is the work of many contributors. You're encouraged to submit pull requests, propose features and discuss issues.
See CONTRIBUTING.
License
Jbuilder is released under the MIT License.