RABL (Ruby API Builder Language) is a Rails and Padrino ruby templating system for generating JSON and XML. When using the ActiveRecord 'to_json' method, I tend to quickly find myself wanting a more expressive and powerful system for generating APIs. This is especially frustrating when the json representation is complex or doesn't match the exact schema defined in the database itself.
I wanted a simple, and flexible system for generating APIs. In particular, I wanted to easily:
- Create arbitrary nodes named based on combining data in an object
- Pass arguments to methods and store the result as a child node
- Partial templates and inheritance to reduce code duplication
- Easily renaming attributes from their name in the model
- Simple way to append attributes from a child into the parent
- Include nodes only if a certain condition is met
Anyone who has tried the 'to_json' method used in ActiveRecord for generating a json response has felt the pain of this restrictive approach. RABL is a general templating system created to solve all of those problems.
Install RABL as a gem:
gem install rabl
or add to your Gemfile:
# Gemfile
gem 'rabl'
and run bundle install
to install the dependency.
If you are using Rails 2.X, Rails 3 or Padrino, RABL works without configuration.
With Sinatra, or any other tilt-based framework, simply register:
Rabl.register!
and RABL will be initialized and ready for use.
To declare the data object for use in the template:
# app/views/users/show.json.rabl
object @user
or a collection works:
object @users
and this will be used as the default data object for the rendering.
Basic usage of the templater to define a few simple attributes for the response:
# app/views/users/show.json.rabl
attributes :id, :foo, :bar
or use with aliased attributes:
# Take the value of model attribute `foo` and name the node `bar`
# { bar : 5 }
attribute :foo => :bar
or even multiple aliased attributes:
# { baz : <bar value>, animal : <dog value> }
attributes :bar => :baz, :dog => :animal
You can also add child nodes from an arbitrary source:
child @posts => :foobar do
attributes :id, :title
end
or simply use existing model associations:
# Renders all the 'posts' association
# from the model into a node called 'foobar'
child :posts => :foobar do
attributes :id, :title
end
You can also append child attributes back to the root node:
# Appends post_id and post_name to parent json object
glue @post do
attributes :id => :post_id, :name => :post_name
end
Use glue to add additional attributes to the parent object.
This will generate a json response based on the result of the code block:
# app/views/users/show.json.rabl
code :full_name do |u|
u.first_name + " " + u.last_name
end
or a custom node that exists only if a condition is true:
# m is the object being rendered, also supports :unless
code(:foo, :if => lambda { |m| m.has_foo? }) do |m|
m.foo
end
You can use custom "code" nodes to create flexible representations of a value utilizing all the data from the model.
Often you need to access sub-objects in order to construct your own custom nodes for more complex associations. You can get access to the rabl representation of another object with:
code :location do
{ :city => @city, :address => partial("web/users/address", :object => @address) }
end
or an object associated to the parent model:
code :location do |m|
{ :city => m.city, :address => partial("web/users/address", :object => m.address) }
end
You can use this method to construct arbitrarily complex nodes for your APIs.
Another common issue of many template builders is unnecessary code redundancy. Typically many representations of an object across multiple endpoints share common attributes or nodes. The nodes for a 'post' object are probably the same or similar in most references throughout the various endpoints.
RABL has the ability to extend other "base" rabl templates and additional attributes:
# app/views/users/advanced.json.rabl
extends "users/base" # another RABL template in "app/views/users/base.json.rabl"
code :can_drink do |m|
m.age > 21
end
You can also extend other rabl templates while constructing child nodes to reduce duplication:
# app/views/users/show.json.rabl
child @address do
extends "address/item"
end
Using partials and inheritance can significantly reduce code duplication in your templates.
Check out the Issues tab for a full list:
- I am sloppy and failed to unit test this as I cobbled it together. Don't use it in production until I do, for now this is a fun experiment.
- No configuration options yet for how to create the json (root nodes) :(
- Better Tilt template support (precompiling templates)
- Benchmarks and performance optimizations
Thanks to Miso for allowing me to create this for our applications and release this project!
- Nathan Esquenazi - Creator of the project
- Arthur Chiu - Core Maintainer, Riot Testing Guru
- Tim Lee - RABL is an awesome name and was chosen by the Miso CTO.
More to come hopefully! Please fork and contribute, any help is appreciated!
There are a few excellent libraries that helped inspire RABL and they are listed below:
Thanks again for all of these great projects.