How can I make a check_box_tag to post a 'false' or '0' parameter when unchecked?

Question

With the following check_box_tag:

<%= check_box_tag 'object[boolean_attribute]', 1, object.boolean_attribute %>

I can update the boolean_attribute in only one direction: from false to true.

When is unchecked by default (because object.boolean_attribute is false) and I check it and then submit the form, a :boolean_attribute => 1 parameter is posted.

But, when I try to update from true to false no param is passed, so the boolean_attribute remains true.

In other words, when is checked by default (because object.boolean_attribute is true) and I uncheck it and then submit the form, a :boolean_attribute => 0 is not posted.

How can I make this check_box_tag to post a :boolean_attribute => 0 parameter when unchecked?

From the api I can't figure out if there is some option to pass to easily achieve it: http://api.rubyonrails.org/classes/ActionView/Helpers/FormTagHelper.html#method-i-check_box_tag

Thank you.

EDIT

For some reason I cannot fathom, in my actual code (with a nested many-to-many association) the hidden_field_tag is not working.

<%= hidden_field_tag 'order[preparations_attributes][][cooked]', nil %>
<%= check_box_tag 'order[preparations_attributes][][cooked]', '1', preparation.cooked? %>

Now I have the opposite problem: I can uncheck the checkbox and the preparation is updated as aspected, but if I check the checkbox it messes up the params.

Here are the posted params for the unchecked box:

Parameters: {"utf8"=>"✓", "authenticity_token"=>"bGgPGbk+Cuk2q+LEgqetmk4e7xie8dB3iMP9Cj3SUm0=", "order"=>{"customer_name"=>"Duccio Armenise", "duedate"=>"2012-04-25 09:24:00.000000", "preparations_attributes"=>[{"quantity"=>"1", "description"=>"custom recipe", "kind"=>"custom", "cooked"=>"", "recipe_id"=>"9", "id"=>"86", "quantities_attributes"=>[{"ingredient_id"=>"", "qty"=>"", "_destroy"=>"0"}, {"ingredient_id"=>"11", "qty"=>"5.0", "id"=>"193", "_destroy"=>"0"}], "_destroy"=>"0"}], "add_preparation"=>{"recipe_id"=>""}}, "continue"=>"Confirm", "id"=>"31"}

Now see what a mess when I check the checkbox, beginning from "cooked"=>" ", for some reason Rails is closing the preparation_attributes hash too early!

Parameters: {"utf8"=>"✓", "authenticity_token"=>"bGgPGbk+Cuk2q+LEgqetmk4e7xie8dB3iMP9Cj3SUm0=", "order"=>{"customer_name"=>"Duccio Armenise", "duedate"=>"2012-04-25 09:24:00.000000", "preparations_attributes"=>[{"quantity"=>"1", "description"=>"custom recipe", "kind"=>"custom", "cooked"=>""}, {"cooked"=>"1", "recipe_id"=>"9", "id"=>"86", "quantities_attributes"=>[{"ingredient_id"=>"", "qty"=>"", "_destroy"=>"0"}, {"ingredient_id"=>"11", "qty"=>"5.0", "id"=>"193", "_destroy"=>"0"}], "_destroy"=>"0"}], "add_preparation"=>{"recipe_id"=>""}}, "continue"=>"Confirm", "id"=>"31"}

EDIT #2:

I think I ran into a Rails bug related to deep nested resource forms and param passing: https://github.com/rails/rails/issues/5937

For now I made it to work with a select_tag:

<%= select_tag 'order[preparations_attributes][][cooked]', options_for_select({yes: 1, no: 0}, preparation.cooked? ? 1 : 0) %>

I think that switching to a select_tag in order to avoid the "hidden_field gotcha" is an acceptable workaround.

Anyway, thank you for the answers!

jdoe jdoe · Accepted Answer · 2012-04-23T12:44:26

check_box (w/o _tag) helper adds hidden field to address your problem for you:

<%= check_box 'object', 'boolean_attribute', {}, 'true', 'false' %>

# result:
<input name="object[boolean_attribute]" type="hidden" value="false" />
<input id="object_boolean_attribute" name="object[boolean_attribute]" type="checkbox" value="true" />

UPD: Dealing with nested resources (Product accepts_nested_attributes_for :line_items)

= form_for @product, url: '' do |f|
  %p
    = f.label :title
    = f.text_field :title

  = f.fields_for :line_items do |li|
    = li.check_box :approved
    = li.label :approved, li.object.id
    %br
  = f.submit

Checking 2 of 3 checkboxes gives me the params as this:

{..., "product"=>{"title"=>"RoR book", "line_items_attributes"=>{"0"=>{"approved"=>"0", "id"=>"47"}, "1"=>{"approved"=>"1", "id"=>"48"}, "2"=>{"approved"=>"1", "id"=>"51"}}}, "commit"=>"Update Product", "action"=>"action1", "controller"=>"test"}

params as YAML for readability:

product:
  title: RoR book
  line_items_attributes:
    '0':
      approved: '0'
      id: '47'
    '1':
      approved: '1'
      id: '48'
    '2':
      approved: '1'
      id: '51'

See? No hidden fields but checked/unchecked states are clearly distinguished.

Having this params allows me to use one line of code to update associated line_items:

@product.update_attributes params[:product]

I hope it helps.

How can I make a check_box_tag to post a 'false' or '0' parameter when unchecked?

5 Answers