Returns a JSON string representing the hash.

Without any options, the returned JSON string will include all the hash keys. For example:

{ :name => "Konata Izumi", 'age' => 16, 1 => 2 }.to_json

{"name": "Konata Izumi", 1: 2, "age": 16}

The keys in the JSON string are unordered due to the nature of hashes.

The :only and :except options can be used to limit the attributes included, and will accept 1 or more hash keys to include/exclude.

{ :name => "Konata Izumi", 'age' => 16, 1 => 2 }.to_json(:only => [:name, 'age'])

{"name": "Konata Izumi", "age": 16}

{ :name => "Konata Izumi", 'age' => 16, 1 => 2 }.to_json(:except => 1)

{"name": "Konata Izumi", "age": 16}

The options also filter down to any hash values. This is particularly useful for converting hashes containing ActiveRecord objects or any object that responds to options in their to_json method. For example:

users = User.find(:all)
{ :users => users, :count => users.size }.to_json(:include => :posts)

would pass the :include => :posts option to users, allowing the posts association in the User model to be converted to JSON as well.

Source Code

# File active_support/json/encoders/hash.rb, line 34
def to_json(options = {}) #:nodoc:
  hash_keys = self.keys

  if options[:except]
    hash_keys = hash_keys - Array(options[:except])
  elsif options[:only]
    hash_keys = hash_keys & Array(options[:only])
  end

  returning result = '{' do
    result << hash_keys.map do |key|
      "#{ActiveSupport::JSON.encode(key)}: #{ActiveSupport::JSON.encode(self[key], options)}"
    end * ', '
    result << '}'
  end
end