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"}]}

Builds an XML document to represent the model. Some configuration is available through options. However more complicated cases should override ActiveRecord::Base#to_xml.

By default the generated XML document will include the processing instruction and all the object‘s attributes. For example:

  <?xml version="1.0" encoding="UTF-8"?>
  <topic>
    <title>The First Topic</title>
    <author-name>David</author-name>
    <id type="integer">1</id>
    <approved type="boolean">false</approved>
    <replies-count type="integer">0</replies-count>
    <bonus-time type="datetime">2000-01-01T08:28:00+12:00</bonus-time>
    <written-on type="datetime">2003-07-16T09:28:00+1200</written-on>
    <content>Have a nice day</content>
    <author-email-address>david@loudthinking.com</author-email-address>
    <parent-id></parent-id>
    <last-read type="date">2004-04-15</last-read>
  </topic>

This behavior can be controlled with :only, :except, :skip_instruct, :skip_types, :dasherize and :camelize . The :only and :except options are the same as for the attributes method. The default is to dasherize all column names, but you can disable this setting :dasherize to false. Setting :camelize to true will camelize all column names - this also overrides :dasherize. To not have the column type included in the XML output set :skip_types to true.

For instance:

  topic.to_xml(:skip_instruct => true, :except => [ :id, :bonus_time, :written_on, :replies_count ])

  <topic>
    <title>The First Topic</title>
    <author-name>David</author-name>
    <approved type="boolean">false</approved>
    <content>Have a nice day</content>
    <author-email-address>david@loudthinking.com</author-email-address>
    <parent-id></parent-id>
    <last-read type="date">2004-04-15</last-read>
  </topic>

To include first level associations use :include:

  firm.to_xml :include => [ :account, :clients ]

  <?xml version="1.0" encoding="UTF-8"?>
  <firm>
    <id type="integer">1</id>
    <rating type="integer">1</rating>
    <name>37signals</name>
    <clients type="array">
      <client>
        <rating type="integer">1</rating>
        <name>Summit</name>
      </client>
      <client>
        <rating type="integer">1</rating>
        <name>Microsoft</name>
      </client>
    </clients>
    <account>
      <id type="integer">1</id>
      <credit-limit type="integer">50</credit-limit>
    </account>
  </firm>

To include deeper levels of associations pass a hash like this:

  firm.to_xml :include => {:account => {}, :clients => {:include => :address}}
  <?xml version="1.0" encoding="UTF-8"?>
  <firm>
    <id type="integer">1</id>
    <rating type="integer">1</rating>
    <name>37signals</name>
    <clients type="array">
      <client>
        <rating type="integer">1</rating>
        <name>Summit</name>
        <address>
          ...
        </address>
      </client>
      <client>
        <rating type="integer">1</rating>
        <name>Microsoft</name>
        <address>
          ...
        </address>
      </client>
    </clients>
    <account>
      <id type="integer">1</id>
      <credit-limit type="integer">50</credit-limit>
    </account>
  </firm>

To include any methods on the model being called use :methods:

  firm.to_xml :methods => [ :calculated_earnings, :real_earnings ]

  <firm>
    # ... normal attributes as shown above ...
    <calculated-earnings>100000000000000000</calculated-earnings>
    <real-earnings>5</real-earnings>
  </firm>

To call any additional Procs use :procs. The Procs are passed a modified version of the options hash that was given to to_xml:

  proc = Proc.new { |options| options[:builder].tag!('abc', 'def') }
  firm.to_xml :procs => [ proc ]

  <firm>
    # ... normal attributes as shown above ...
    <abc>def</abc>
  </firm>

Alternatively, you can yield the builder object as part of the to_xml call:

  firm.to_xml do |xml|
    xml.creator do
      xml.first_name "David"
      xml.last_name "Heinemeier Hansson"
    end
  end

  <firm>
    # ... normal attributes as shown above ...
    <creator>
      <first_name>David</first_name>
      <last_name>Heinemeier Hansson</last_name>
    </creator>
  </firm>

As noted above, you may override to_xml in your ActiveRecord::Base subclasses to have complete control about what‘s generated. The general form of doing this is:

  class IHaveMyOwnXML < ActiveRecord::Base
    def to_xml(options = {})
      options[:indent] ||= 2
      xml = options[:builder] ||= Builder::XmlMarkup.new(:indent => options[:indent])
      xml.instruct! unless options[:skip_instruct]
      xml.level_one do
        xml.tag!(:second_level, 'content')
      end
    end
  end