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https://github.com/ccocchi/rabl-rails

Rails 4.2+ templating system with JSON, XML and Plist support.
https://github.com/ccocchi/rabl-rails

json rabl-template rails ruby

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Rails 4.2+ templating system with JSON, XML and Plist support.

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# RABL for Rails [![Build Status](https://travis-ci.org/ccocchi/rabl-rails.svg?branch=master)](https://travis-ci.org/ccocchi/rabl-rails)



`rabl-rails` is a ruby templating system for rendering your objects in different format (JSON, XML, PLIST).



This gem aims for speed and little memory footprint while letting you build complex response with a very intuitive DSL.



`rabl-rails` targets **Rails 4.2/5/6 application** and have been testing with MRI and jRuby.



## Installation



Install as a gem :



```

gem install rabl-rails

```



or add directly to your `Gemfile`



```

gem 'rabl-rails', '~> 0.6.0'

```



## Overview



The gem enables you to build responses using views like you would using HTML/erb/haml.

As example, assuming you have a `Post` model filled with blog posts, and a `PostController` that look like this:



```ruby

class PostController < ApplicationController

  def index

	 @posts = Post.order('created_at DESC')

  end

end

```



You can create the following RABL-rails template to express the API output of `@posts`



```ruby

# app/views/post/index.rabl

collection :@posts



attributes :id, :title, :subject

child(:user) { attributes :full_name }

node(:read) { |post| post.read_by?(@user) }

```



This would output the following JSON when visiting `http://localhost:3000/posts.json`



```js

[{

  "id" : 5, title: "...", subject: "...",

  "user" : { full_name : "..." },

  "read" : true

}]

```



## How it works



This gem separates compiling, ie. transforming a RABL-rails template into a Ruby hash, and the actual rendering of the object or collection. This allows to only compile the template once (when template caching is enabled) which is the slow part, and only use hashes during rendering.



The drawback of compiling the template outside of any rendering context is that we can't access instance variables like usual. Instead, you'll mostly use symbols representing your variables and the gem will retrieve them when needed.



There are places where the gem allows for "dynamic code" -- code that is evaluated at each rendering, such as within `node` or `condition` blocks.



```ruby

# We reference the @posts varibles that will be used at rendering time

collection :@posts



# Here you can use directly the instance variable because it

# will be evaluated when rendering the object

node(:read) { |post| post.read_by?(@user) }

```



The same rule applies for view helpers such as `current_user`



After the template is compiled into a hash, `rabl-rails` will use a renderer to create the actual output. Currently, JSON, XML and PList formats are supported.



## Configuration



RablRails works out of the box, with default options and fastest engine available (oj, libxml). But depending on your needs, you might want to change that or how your output looks like. You can set global configuration in your application:



```ruby

# config/initializers/rabl_rails.rb



RablRails.configure do |config|

  # These are the default

  # config.cache_templates = true

  # config.include_json_root = true

  # config.json_engine = ::Oj

  # config.xml_options = { :dasherize => true, :skip_types => false }

  # config.enable_jsonp_callbacks = false

  # config.replace_nil_values_with_empty_strings = false

  # config.replace_empty_string_values_with_nil = false

  # config.exclude_nil_values = false

  # config.non_collection_classes = Set.new(['Struct'])

end

```



## Usage



### Data declaration



To declare data to use in the template, you can use either `object` or `collection` with the symbol name or your data.



```ruby

# app/views/users/show.json.rabl

object :@user



# app/views/users/index.json.rabl

collection :@users

```



You can specify root label for the collection using hash or `:root` option



```ruby

collection :@posts, root: :articles

#is equivalent to

collection :@posts => :articles



# => { "articles" : [{...}, {...}] }

```



There are rares cases when the template doesn't map directly to any object. In these cases, you can set data to false.



```ruby

object false

node(:some_count) { |_| @user.posts.count }

child(:@user) { attribute :name }

```



If you use gems like *decent_exposure* or *focused_controller*, you can use your variable directly without the leading `@`



```ruby

object :object_exposed

```



### Attributes / Methods



Adds a new field to the response object, calling the method on the object being rendered. Methods called this way should return natives types from the format you're using (such as `String`, `integer`, etc for JSON). For more complex objects, see `child` nodes.



```ruby

attributes :id, :title, :to_s

```



You can aliases these attributes in your response



```ruby

attributes :my_custom_method, as: :title

# => { "title" :  }

```



or show attributes based on a condition. The currently rendered object is given to the `proc` condition.



```ruby

attributes :published_at, :anchor, if: ->(post) { post.published? }

```



### Child nodes



Changes the object being rendered for the duration of the block. Depending on if you use `node` or `glue`, the result will be added as a new field or merged respectively.



Data passed can be a method or a reference to an instance variable.



For example if you have a `Post` model that belongs to a `User` and want to add the user's name to your response.



```ruby

object :@post



child(:user, as: :author) do

	attributes :name

end

# => { "post": { "author" : { "name" : "John D." } } }

```



If instead of having an `author` node in your response you wanted the name at the root level, you can use `glue`:



```ruby

object :@post



glue(:user) do

  attributes :name, as: :author_name

end

# => { "post": { "author_name" : "John D." } }

```



Arbitrary data source can also be passed:



```ruby

# in your controller

# @custom_data = [...]



# in the view

child(:@custom_data) do

	attributes :id, :name

end

# => { "custom_data": [...] }

```



You can use a Hash-like data source, as long as keys match a method or attribute of your main resource, using the `fetch` keyword:



```ruby

# assuming you have something similar in your controller

# @users_hash = { 1 => User.new(pseudo: 'Batman') }



# in the view

object :@post



fetch(:@users_hash, as: :user, field: :user_id) do

  attributes :pseudo

end

# => { user: { pseudo: 'Batman' } }

```



This comes very handy when adding attributes from external queries not really bound to a relation, like statistics.



### Constants



Adds a new field to the response using an immutable value.



```ruby

const(:api_version, API::VERSION)

const(:locale, 'fr_FR')

```



### Lookups



Adds a new field to the response, using rendered resource's id by default or any method to fetch a value from the given hash variable.



```ruby

collection :@posts



lookup(:comments_count, :@comments_count, field: :uuid, cast: false)

# => [{ "comments_count": 3 }, { "comments_count": 6 }]

```



In the example above, for each post it will fetch the value from `@comments_count` using the post's `uuid` as key. When the `cast` value is set to `true` (it is `false` by default), the value will be casted to a boolean using `!!`.



### Custom nodes



Adds a new field to the response with block's result as value.



```ruby

object :@user

node(:full_name) { |u| u.first_name + " " + u.last_name }

# => { "user" : { "full_name" : "John Doe" } }

```



You can add condition on your custom nodes. If the condition evaluates to a falsey value, the node will not added to the response at all.



```ruby

node(:email, if: ->(u) { u.valid_email? }) do |u|

	u.email

end

```



Nodes are evaluated at rendering time, so you can use any instance variables or view helpers within them



```ruby

node(:url) { |post| post_url(post) }

```



If the result of the block is a Hash, it can be directly merge into the response using `merge` instead of `node`



```ruby

object :@user

merge { |u| { name: u.first_name + " " + u.last_name } }

# => { "user" : { "name" : "John Doe" } }

```



### Extends & Partials



Often objects have a basic representation that is shared accross different views and enriched according to it. To avoid code redundancy you can extend your template from any other RABL template.



```ruby

# app/views/shared/_user.rabl

attributes :id, :name



# app/views/users/show.rabl

object :@user



extends('shared/_user')

attributes :super_secret_attribute



#=> { "id": 1, "name": "John", "super_secret_attribute": "Doe" }

```



When used with child node, if they are the only thing added you can instead use the `partial` option directly.



```ruby

child(:user, partial: 'shared/_user')



# is equivalent to



child(:user) do

  extends('shared/_user')

end

```



Extends can be used dynamically using rendered object and lambdas.



```ruby

extends ->(user) { "shared/_#{user.client_type}_infos" }

```



Partials can also be used inside custom nodes. When using partial this way, you MUST declare the `object` associated to the partial



```ruby

node(:location) do |user|

	{ city: user.city, address: partial('users/address', object: m.address) }

end

```



When used this way, partials can take locals variables that can be accessed in the included template.



```ruby

# _credit_card.rabl

node(:credit_card, if: ->(u) { locals[:display_credit_card] }) do |user|

  user.credit_card_info

end



# user.json.rabl

merge { |u| partial('_credit_card', object: u, locals: { display_credit_card: true }) }

```



### Putting it all together



`rabl-rails` allows you to format your responses easily, from simple objects to hierarchy of 2 or 3 levels.



```ruby

object :@thread



attribute :caption, as: :title



child(:@sorted_posts, as: :posts) do

  attributes :title, :slug



  child :comments do

		extends 'shared/_comment'

    lookup(:upvotes, :@upvotes_per_comment)

	end

end

```



### Other features



* [Caching](https://github.com/ccocchi/rabl-rails/wiki/Caching)



And more in the [WIKI](https://github.com/ccocchi/rabl-rails/wiki)



## Performance



Benchmarks have been made using this [application](http://github.com/ccocchi/rabl-benchmark), with rabl 0.13.1 and rabl-rails 0.5.0



Overall, rabl-rails is **10% faster and use 10% less memory**, but these numbers skyrockets to **50%** when using `extends` with collection of objects.



You can see full tests on test application repository.



## Authors and contributors



* [Christopher Cocchi-Perrier](http://github.com/ccocchi) - Creator of the project



Want to add another format to Rabl-rails ? Checkout [JSON renderer](http://github.com/ccocchi/rabl-rails/blob/master/lib/rabl-rails/renderers/json.rb) for reference

Want to make another change ? Just fork and contribute, any help is very much appreciated. If you found a bug, you can report it via the Github issues.



## Original idea



* [RABL](http://github.com/nesquena/rabl) Standart RABL gem. I used it a lot but I needed to improve my API response time, and since most of the time was spent in view rendering, I decided to implement a faster rabl gem.



## Copyright



Copyright © 2012-2020 Christopher Cocchi-Perrier. See [MIT-LICENSE](http://github.com/ccocchi/rabl-rails/blob/master/MIT-LICENSE) for details.