grouped_collection_select(object, method, collection, group_method, group_label_method, option_key_method, option_value_method, options = {}, html_options = {}) public

Returns <select>, <optgroup> and <option> tags for the collection of existing return values of method for object's class. The value returned from calling method on the instance object will be selected. If calling method returns nil, no selection is made without including :prompt or :include_blank in the options hash.

Parameters:

  • object - The instance of the class to be used for the select tag
  • method - The attribute of object corresponding to the select tag
  • collection - An array of objects representing the <optgroup> tags.
  • group_method - The name of a method which, when called on a member of collection, returns an array of child objects representing the <option> tags.
  • group_label_method - The name of a method which, when called on a member of collection, returns a string to be used as the label attribute for its <optgroup> tag.
  • option_key_method - The name of a method which, when called on a child object of a member of collection, returns a value to be used as the value attribute for its <option> tag.
  • option_value_method - The name of a method which, when called on a child object of a member of collection, returns a value to be used as the contents of its <option> tag.

Example object structure for use with this method: 

  class Continent < ActiveRecord::Base
    has_many :countries
    # attribs: id, name
  end
  class Country < ActiveRecord::Base
    belongs_to :continent
    # attribs: id, name, continent_id
  end
  class City < ActiveRecord::Base
    belongs_to :country
    # attribs: id, name, country_id
  end

Sample usage: 

  grouped_collection_select(:city, :country_id, @continents, :countries, :name, :id, :name)

Possible output: 

  <select name="city[country_id]">
    <optgroup label="Africa">
      <option value="1">South Africa</option>
      <option value="3">Somalia</option>
    </optgroup>
    <optgroup label="Europe">
      <option value="7" selected="selected">Denmark</option>
      <option value="2">Ireland</option>
    </optgroup>
  </select>
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December 16, 2014
2 thanks

Group method chain

The group_method parameter can be a string representing a method chain:

grouped_collection_select(:city, :country_id, @continents, 'countries.sort.reverse', :name, :id, :name)

If we were to modify the Country model so we can sort by name:

class Country
  include Comparable

  def <=>(other)
    self.name <=> other.name
  end
end

The above example would have given us the countries sorted by name in descending sequence.

October 1, 2014
0 thanks

Preselecting options

To preselect options, pass in the selected options in the options hash:

{ :selected => [ selected_option_1, selected__option_2, ... ] }

Code example 

grouped_collection_select(:city, :country_id, @continents, :countries, :name, :id, :name, { :selected => [1, 5, 6 ] } )