module ActionView::Helpers::FormOptionsHelper

include_hidden: false option to the helper method.
In the rare case you don't want this hidden field, you can pass the

blank value.
This hidden field is given the same field name as the checkboxes with a
for every collection of checkboxes.
This is possible thanks to a hidden field generated by the helper method

will not be updated.
If no +category_ids+ are selected then we can safely assume this field

@user.update(params[:user])

have the following code in our update action:
For example, if we have a +User+ model with +category_ids+ field and we

web browsers will not send any value.
When no selection is made for a collection of checkboxes most

==== Gotcha

end
b.label(:"data-value" => b.value) { b.check_box + b.text }
collection_check_boxes(:post, :author_ids, Author.all, :id, :name_with_initial) do |b|
respectively. You can use them like this:
value, which are the current item being rendered, its text and value methods,
There are also three special methods available: object, text and

end
b.label(class: "check_box") { b.check_box(class: "check_box") }
collection_check_boxes(:post, :author_ids, Author.all, :id, :name_with_initial) do |b|
extra HTML options:
The builder methods label and check_box also accept

use the label as wrapper, as in the example above.
Using it, you can change the label and check box display order or even
for the current item in the collection, with proper text and value.
collection, which has the ability to generate the label and check box
The argument passed to the block is a special kind of builder for this

end
b.label { b.check_box }
collection_check_boxes(:post, :author_ids, Author.all, :id, :name_with_initial) do |b|
giving a block to the method:
It is also possible to customize the way the elements will be shown by


M. Clark

D. Thomas

D. Heinemeier Hansson

If @post.author_ids is already [1], this would return:

collection_check_boxes(:post, :author_ids, Author.all, :id, :name_with_initial)
Sample usage (selecting the associated Author for an instance of Post, @post):

end
end
"#{first_name.first}. #{last_name}"
def name_with_initial
has_and_belongs_to_many :posts
class Author < ActiveRecord::Base
end
has_and_belongs_to_many :authors
class Post < ActiveRecord::Base
Example object structure for use with this method:

retrieve the value/text.
as a +proc+, that will be called for each member of the +collection+ to
respectively. They can also be any object that responds to +call+, such
are used as the +value+ attribute and contents of each check box tag,
methods to be called on each member of +collection+. The return values
The :value_method and :text_method parameters are

+nil+, no selection is made.
on the instance +object+ will be selected. If calling +method+ returns
+method+ for +object+'s class. The value returned from calling +method+
Returns check box tags for the collection of existing return values of

def collection_check_boxes(object, method, collection, value_method, text_method, options = {}, html_options = {}, &block)
  Tags::CollectionCheckBoxes.new(object, method, self, collection, value_method, text_method, options, html_options).render(&block)
end

include_hidden: false option.
In case if you don't want the helper to generate this hidden field you can specify

every collection of radio buttons. The hidden field has the same name as collection radio button and blank value.
To prevent this the helper generates an auxiliary hidden field before

will raise an error since no {user: ...} will be present.

params.require(:user).permit(...)

any strong parameters idiom like:
if a +User+ model has a +category_id+ field and in the form no category is selected, no +category_id+ parameter is sent. So,
Unfortunately this introduces a gotcha:
web browsers do not send any value to server.
The HTML specification says when nothing is selected on a collection of radio buttons

==== Gotcha

end
b.label(:"data-value" => b.value) { b.radio_button + b.text }
collection_radio_buttons(:post, :author_id, Author.all, :id, :name_with_initial) do |b|
respectively. You can use them like this:
value, which are the current item being rendered, its text and value methods,
There are also three special methods available: object, text and

end
b.label(class: "radio_button") { b.radio_button(class: "radio_button") }
collection_radio_buttons(:post, :author_id, Author.all, :id, :name_with_initial) do |b|
extra HTML options:
The builder methods label and radio_button also accept

even use the label as wrapper, as in the example above.
Using it, you can change the label and radio button display order or
for the current item in the collection, with proper text and value.
collection, which has the ability to generate the label and radio button
The argument passed to the block is a special kind of builder for this

end
b.label { b.radio_button }
collection_radio_buttons(:post, :author_id, Author.all, :id, :name_with_initial) do |b|
giving a block to the method:
It is also possible to customize the way the elements will be shown by

M. Clark

D. Thomas

D. Heinemeier Hansson

If @post.author_id is already 1, this would return:

collection_radio_buttons(:post, :author_id, Author.all, :id, :name_with_initial)
Sample usage (selecting the associated Author for an instance of Post, @post):

end
end
"#{first_name.first}. #{last_name}"
def name_with_initial

has_many :posts
class Author < ActiveRecord::Base

end
belongs_to :author
class Post < ActiveRecord::Base

Example object structure for use with this method:

retrieve the value/text.
as a +proc+, that will be called for each member of the +collection+ to
respectively. They can also be any object that responds to +call+, such
are used as the +value+ attribute and contents of each radio button tag,
methods to be called on each member of +collection+. The return values
The :value_method and :text_method parameters are

returns +nil+, no selection is made.
+method+ on the instance +object+ will be selected. If calling +method+
of +method+ for +object+'s class. The value returned from calling
Returns radio button tags for the collection of existing return values

def collection_radio_buttons(object, method, collection, value_method, text_method, options = {}, html_options = {}, &block)
  Tags::CollectionRadioButtons.new(object, method, self, collection, value_method, text_method, options, html_options).render(&block)
end

M. Clark
D. Thomas
D. Heinemeier Hansson
Please select

If @post.author_id is already 1, this would return:

collection_select(:post, :author_id, Author.all, :id, :name_with_initial, prompt: true)

Sample usage (selecting the associated Author for an instance of Post, @post):

end
end
"#{first_name.first}. #{last_name}"
def name_with_initial

has_many :posts
class Author < ActiveRecord::Base

end
belongs_to :author
class Post < ActiveRecord::Base

Example object structure for use with this method:

retrieve the value/text.
as a +proc+, that will be called for each member of the +collection+ to
tag, respectively. They can also be any object that responds to +call+, such
of +collection+. The return values are used as the +value+ attribute and contents of each
The :value_method and :text_method parameters are methods to be called on each member

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

def collection_select(object, method, collection, value_method, text_method, options = {}, html_options = {})
  Tags::CollectionSelect.new(object, method, self, collection, value_method, text_method, options, html_options).render
end

def extract_selected_and_disabled(selected)
  if selected.is_a?(Proc)
    [selected, nil]
  else
    selected = Array.wrap(selected)
    options = selected.extract_options!.symbolize_keys
    selected_items = options.fetch(:selected, selected)
    [selected_items, options[:disabled]]
  end
end

def extract_values_from_collection(collection, value_method, selected)
  if selected.is_a?(Proc)
    collection.filter_map do |element|
      element.public_send(value_method) if selected.call(element)
    end
  else
    selected
  end
end

Ireland
Denmark


Somalia
South Africa



Possible output:

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

Sample usage:

end
belongs_to :country
class City < ActiveRecord::Base
# attributes: id, name, country_id

end
belongs_to :continent
class Country < ActiveRecord::Base
# attributes: id, name, continent_id

end
has_many :countries
class Continent < ActiveRecord::Base
# attributes: id, name

Example object structure for use with this method:

+collection+, returns a value to be used as the contents of its 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 +value+ attribute for its tag.
* +option_key_method+ - The name of a method which, when called on a child object of a member of
retrieve the label.
that responds to +call+, such as a +proc+, that will be called for each member of the +collection+ to
string to be used as the +label+ attribute for its tag. It can also be any object
* +group_label_method+ - The name of a method which, when called on a member of +collection+, returns a
value.
to +call+, such as a +proc+, that will be called for each member of the +collection+ to retrieve the
array of child objects representing the tags. It can also be any object that responds
* +group_method+ - The name of a method which, when called on a member of +collection+, returns an
* +collection+ - An array of objects representing the tags.
* +method+ - The attribute of +object+ corresponding to the select tag
* +object+ - The instance of the class to be used for the select tag
Parameters:

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

def grouped_collection_select(object, method, collection, group_method, group_label_method, option_key_method, option_value_method, options = {}, html_options = {})
  Tags::GroupedCollectionSelect.new(object, method, self, collection, group_method, group_label_method, option_key_method, option_value_method, options, html_options).render
end

wrap the output in an appropriate tag.
Note: Only the and tags are returned, so you still have to


France
Germany
Denmark


Canada
United States

Possible output:

grouped_options_for_select(grouped_options, nil, divider: '---------')
]
['Denmark','Germany','France']
[['United States','US'], 'Canada'],
grouped_options = [

* :divider - the divider for the options groups.
prepends an option with a generic prompt - "Please select" - or the given prompt string.
* :prompt - set to true or a prompt string. When the select element doesn't have a value yet, this
Options:

as you might have the same option in multiple groups. Each will then get selected="selected".
which will have the +selected+ attribute set. Note: It is possible for this value to match multiple options
* +selected_key+ - A value equal to the +value+ attribute for one of the tags,
Ex. ["North America",[["United States","US"],["Canada","CA"]], { disabled: "disabled" }]
An optional third value can be provided as HTML attributes for the optgroup.
Ex. ["North America",[["United States","US"],["Canada","CA"]]]
nested array of text-value pairs. See options_for_select for more info.
label while the second value must be an array of options. The second value can be a
* +grouped_options+ - Accepts a nested array or hash of strings. The first value serves as the
Parameters:


France
Germany
Denmark


Canada
United States

Possible output:

grouped_options_for_select(grouped_options)
}
'Europe' => ['Denmark','Germany','France']
'North America' => [['United States','US'], 'Canada'],
grouped_options = {

grouped_options_for_select(grouped_options)
]
['Denmark','Germany','France']]
['Europe',
[['United States','US'],'Canada']],
['North America',
grouped_options = [

wraps them with tags:
Returns a string of tags, like options_for_select, but

def grouped_options_for_select(grouped_options, selected_key = nil, options = {})
  prompt  = options[:prompt]
  divider = options[:divider]
  body = "".html_safe
  if prompt
    body.safe_concat content_tag("option", prompt_text(prompt), value: "")
  end
  grouped_options.each do |container|
    html_attributes = option_html_attributes(container)
    if divider
      label = divider
    else
      label, container = container
    end
    html_attributes = { label: label }.merge!(html_attributes)
    body.safe_concat content_tag("optgroup", options_for_select(container, selected_key), html_attributes)
  end
  body
end

def option_groups_from_collection_for_select(collection, group_method, group_label_method, option_key_method, option_value_method, selected_key = nil)

wrap the output in an appropriate

tag.
Note: Only the and tags are returned, so you still have to


...
Japan
India
China


...
Rwanda
Egypt

Possible output:

option_groups_from_collection_for_select(@continents, :countries, :name, :id, :name, 3)
Sample usage:

end
# attribs: id, name, continent_id
belongs_to :continent
class Country < ActiveRecord::Base

end
# attribs: id, name
has_many :countries
class Continent < ActiveRecord::Base

Example object structure for use with this method:

to be specified.
to +option_key_method+. If +nil+, no selection is made. Can also be a hash if disabled values are
which will have the +selected+ attribute set. Corresponds to the return value of one of the calls
* +selected_key+ - A value equal to the +value+ attribute for one of the tags,
+collection+, returns a value to be used as the contents of its 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 +value+ attribute for its tag.
* +option_key_method+ - The name of a method which, when called on a child object of a member of
string to be used as the +label+ attribute for its tag.
* +group_label_method+ - The name of a method which, when called on a member of +collection+, returns a
array of child objects representing the tags.
* +group_method+ - The name of a method which, when called on a member of +collection+, returns an
* +collection+ - An array of objects representing the tags.
Parameters:

groups them by tags based on the object relationships of the arguments.
Returns a string of tags, like options_from_collection_for_select, but

def option_groups_from_collection_for_select(collection, group_method, group_label_method, option_key_method, option_value_method, selected_key = nil)
  collection.map do |group|
    option_tags = options_from_collection_for_select(
      value_for_collection(group, group_method), option_key_method, option_value_method, selected_key)
    content_tag("optgroup", option_tags, label: value_for_collection(group, group_label_method))
  end.join.html_safe
end