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method

to_json

Importance_5
Ruby on Rails latest stable (v4.1.8) - 3 notes - Class: ActiveRecord::Serialization

Method deprecated or moved

This method is deprecated or moved on the latest stable version. The last existing version (v2.3.8) is shown here.

These similar methods exist in v4.1.8:

to_json(options = {}) public

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

The option ActiveRecord::Base.include_root_in_json controls the top-level behavior of to_json. In a new Rails application, it is set to true in initializers/new_rails_defaults.rb. When it is true, to_json will emit a single root node named after the object’s type. For example:

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

  ActiveRecord::Base.include_root_in_json = false
  konata.to_json
  # => {"id": 1, "name": "Konata Izumi", "age": 16,
        "created_at": "2006/08/01", "awesome": true}

The remainder of the examples in this section assume include_root_in_json is set to false.

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"}]}
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September 1, 2008 - (>= v2.1.0)
5 thanks

ActiveRecord::Base.include_root_in_json

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
April 29, 2009 - (<= v2.3.2)
1 thank

Including instance methods to JSON output

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.

March 3, 2009 - (<= v2.2.1)
1 thank

Multiple associations on the same level

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"}]}