Add nested fields in JSON output in Rails controller

Question

At the end of a standard Rails controller there is:

respond_to do |format| format.html format.json { render json: @cars } end 

Works as expected. Except the JSON doesn't have the associations of @cars:

class Car < ActiveRecord::Base attr_accessible :model, :color belongs_to :manufacturer end 

The JSON doesn't have the fields of the manufacturer. How do I get the JSON to have those? Is there something I add to the belongs_to call? Is there a way I can add it to the object created from format.json?

Answer 1

By default, as_json, the method, that converts an object to JSON, includes all attributes. But manufacturer is is a method.

You can instruct as_json to include the manufacturer with the option :methods, see api doc.

So your Car model could loo like

class Car < ActiveRecord::Base belongs_to :manufacturer def as_json(options={}) super(options.merge methods: :manufacturer_json) end def manufacturer_json manufacturer.as_json end end 

to include the manufacturer.

Answer 2

My favorite way to do this is with the Active Model Serializer gem. With the use of custom serializers, you can achieve almost any JSON structure you'd like, with the exception of using Active Model Serializer for Has Many Through associations, which is currently being overhauled.

You might want to take a look at some tutorials like http://robots.thoughtbot.com/fast-json-apis-in-rails-with-key-based-caches-and