/ Ruby on Rails
/
method

to_json

to_json(options = {})
public

Returns a JSON string representing the model. Some configuration is available through options.

Without any options, the returned JSON string will include all the model’s attributes. For example: 

  konata = User.find(1)
  konata.to_json
  # => {"id": 1, "name": "Konata Izumi", "age": 16,
        "created_at": "2006/08/01", "awesome": true}

The :only and :except options can be used to limit the attributes included, and work similar to the attributes method. For example: 

  konata.to_json(:only => [ :id, :name ])
  # => {"id": 1, "name": "Konata Izumi"}

  konata.to_json(:except => [ :id, :created_at, :age ])
  # => {"name": "Konata Izumi", "awesome": true}

To include any methods on the model, use :methods. 

  konata.to_json(:methods => :permalink)
  # => {"id": 1, "name": "Konata Izumi", "age": 16,
        "created_at": "2006/08/01", "awesome": true,
        "permalink": "1-konata-izumi"}

To include associations, use :include. 

  konata.to_json(:include => :posts)
  # => {"id": 1, "name": "Konata Izumi", "age": 16,
        "created_at": "2006/08/01", "awesome": true,
        "posts": [{"id": 1, "author_id": 1, "title": "Welcome to the weblog"},
                  {"id": 2, author_id: 1, "title": "So I was thinking"}]}

2nd level and higher order associations work as well: 

  konata.to_json(:include => { :posts => {
                                 :include => { :comments => {
                                               :only => :body } },
                                 :only => :title } })
  # => {"id": 1, "name": "Konata Izumi", "age": 16,
        "created_at": "2006/08/01", "awesome": true,
        "posts": [{"comments": [{"body": "1st post!"}, {"body": "Second!"}],
                   "title": "Welcome to the weblog"},
                  {"comments": [{"body": "Don't think too hard"}],
                   "title": "So I was thinking"}]}

3Notes

ActiveRecord::Base.include_root_in_json

felixmcallister · Sep 1, 20085 thanks

From Rails 2.1 onwards, the variable

ActiveRecord::Base.include_root_in_json

affects how the JSON is generated. If this is true (default), then the JSON isn't like the one above. Instead you'll get:

konata = User.find(1)
konata.to_json
# => { "user": { "id": 1, "name": "Konata Izumi", "age": 16,
    "created_at": "2006/08/01", "awesome": true}}

(Note the model name is included as a root of the JSON object)

For Rails 2.1 generated projects, you'll see this in the config/initializers/new_rails_defaults.rb file. You'll need to set the value to false if you want the old behaviour.

ActiveRecord::Base.include_root_in_json = false

Multiple associations on the same level

batasrki · Mar 2, 20091 thank

You can also specify multiple associations that are on the same level, like this:

konata = User.find(1)
konata.to_json(:include => [:posts, :roles])

{"id": 1, "name": "Konata Izumi", "age": 16,

"created_at": "2006/08/01", "awesome": true, "posts": [{"id": 1, "author_id": 1, "title": "Welcome to the weblog"}, {"id": 2, author_id: 1, "title": "So I was thinking"}], "roles": [{"id":1, "user_id":1, "name": "Admin"}, {"id":2, "user_id":1, "name": "Moderator"}]}

Including instance methods to JSON output

pekkaj · Apr 29, 20091 thank

Use :methods parameter to include ActiveRecord instance methods to JSON output. :only and :except uses DB columns only.

@events.to_json(:include => { 
                :images => { 
                  :only => [], :methods => [:public_url] }})

In the previous example events have multiple images and only public_url instance method is included in the JSON output.