Returns a checkbox tag tailored for accessing a specified attribute (identified by method) on an object assigned to the template (identified by object). This object must be an instance object (@object) and not a local object. It‘s intended that method returns an integer and if that integer is above zero, then the checkbox is checked. Additional options on the input tag can be passed as a hash with options. The checked_value defaults to 1 while the default unchecked_value is set to 0 which is convenient for boolean values.

Gotcha

The HTML specification says unchecked check boxes are not successful, and thus web browsers do not send them. Unfortunately this introduces a gotcha: if an Invoice model has a paid flag, and in the form that edits a paid invoice the user unchecks its check box, no paid parameter is sent. So, any mass-assignment idiom like

  @invoice.update_attributes(params[:invoice])

wouldn‘t update the flag.

To prevent this the helper generates a hidden field with the same name as the checkbox after the very check box. So, the client either sends only the hidden field (representing the check box is unchecked), or both fields. Since the HTML specification says key/value pairs have to be sent in the same order they appear in the form and Rails parameters extraction always gets the first occurrence of any given key, that works in ordinary forms.

Unfortunately that workaround does not work when the check box goes within an array-like parameter, as in

  <% fields_for "project[invoice_attributes][]", invoice, :index => nil do |form| %>
    <%= form.check_box :paid %>
    ...
  <% end %>

because parameter name repetition is precisely what Rails seeks to distinguish the elements of the array.

Examples

  # Let's say that @post.validated? is 1:
  check_box("post", "validated")
  # => <input type="checkbox" id="post_validated" name="post[validated]" value="1" />
  #    <input name="post[validated]" type="hidden" value="0" />

  # Let's say that @puppy.gooddog is "no":
  check_box("puppy", "gooddog", {}, "yes", "no")
  # => <input type="checkbox" id="puppy_gooddog" name="puppy[gooddog]" value="yes" />
  #    <input name="puppy[gooddog]" type="hidden" value="no" />

  check_box("eula", "accepted", { :class => 'eula_check' }, "yes", "no")
  # => <input type="checkbox" class="eula_check" id="eula_accepted" name="eula[accepted]" value="yes" />
  #    <input name="eula[accepted]" type="hidden" value="no" />

Creates a scope around a specific model object like form_for, but doesn‘t create the form tags themselves. This makes fields_for suitable for specifying additional model objects in the same form.

Generic Examples

  <% form_for @person, :url => { :action => "update" } do |person_form| %>
    First name: <%= person_form.text_field :first_name %>
    Last name : <%= person_form.text_field :last_name %>

    <% fields_for @person.permission do |permission_fields| %>
      Admin?  : <%= permission_fields.check_box :admin %>
    <% end %>
  <% end %>

…or if you have an object that needs to be represented as a different parameter, like a Client that acts as a Person:

  <% fields_for :person, @client do |permission_fields| %>
    Admin?: <%= permission_fields.check_box :admin %>
  <% end %>

…or if you don‘t have an object, just a name of the parameter:

  <% fields_for :person do |permission_fields| %>
    Admin?: <%= permission_fields.check_box :admin %>
  <% end %>

Note: This also works for the methods in FormOptionHelper and DateHelper that are designed to work with an object as base, like FormOptionHelper#collection_select and DateHelper#datetime_select.

Nested Attributes Examples

When the object belonging to the current scope has a nested attribute writer for a certain attribute, fields_for will yield a new scope for that attribute. This allows you to create forms that set or change the attributes of a parent object and its associations in one go.

Nested attribute writers are normal setter methods named after an association. The most common way of defining these writers is either with accepts_nested_attributes_for in a model definition or by defining a method with the proper name. For example: the attribute writer for the association :address is called address_attributes=.

Whether a one-to-one or one-to-many style form builder will be yielded depends on whether the normal reader method returns a single object or an array of objects.

One-to-one

Consider a Person class which returns a single Address from the address reader method and responds to the address_attributes= writer method:

  class Person
    def address
      @address
    end

    def address_attributes=(attributes)
      # Process the attributes hash
    end
  end

This model can now be used with a nested fields_for, like so:

  <% form_for @person, :url => { :action => "update" } do |person_form| %>
    ...
    <% person_form.fields_for :address do |address_fields| %>
      Street  : <%= address_fields.text_field :street %>
      Zip code: <%= address_fields.text_field :zip_code %>
    <% end %>
  <% end %>

When address is already an association on a Person you can use accepts_nested_attributes_for to define the writer method for you:

  class Person < ActiveRecord::Base
    has_one :address
    accepts_nested_attributes_for :address
  end

If you want to destroy the associated model through the form, you have to enable it first using the :allow_destroy option for accepts_nested_attributes_for:

  class Person < ActiveRecord::Base
    has_one :address
    accepts_nested_attributes_for :address, :allow_destroy => true
  end

Now, when you use a form element with the _destroy parameter, with a value that evaluates to true, you will destroy the associated model (eg. 1, ‘1’, true, or ‘true’):

  <% form_for @person, :url => { :action => "update" } do |person_form| %>
    ...
    <% person_form.fields_for :address do |address_fields| %>
      ...
      Delete: <%= address_fields.check_box :_destroy %>
    <% end %>
  <% end %>

One-to-many

Consider a Person class which returns an array of Project instances from the projects reader method and responds to the projects_attributes= writer method:

  class Person
    def projects
      [@project1, @project2]
    end

    def projects_attributes=(attributes)
      # Process the attributes hash
    end
  end

This model can now be used with a nested fields_for. The block given to the nested fields_for call will be repeated for each instance in the collection:

  <% form_for @person, :url => { :action => "update" } do |person_form| %>
    ...
    <% person_form.fields_for :projects do |project_fields| %>
      <% if project_fields.object.active? %>
        Name: <%= project_fields.text_field :name %>
      <% end %>
    <% end %>
  <% end %>

It‘s also possible to specify the instance to be used:

  <% form_for @person, :url => { :action => "update" } do |person_form| %>
    ...
    <% @person.projects.each do |project| %>
      <% if project.active? %>
        <% person_form.fields_for :projects, project do |project_fields| %>
          Name: <%= project_fields.text_field :name %>
        <% end %>
      <% end %>
    <% end %>
  <% end %>

Or a collection to be used:

  <% form_for @person, :url => { :action => "update" } do |person_form| %>
    ...
    <% person_form.fields_for :projects, @active_projects do |project_fields| %>
      Name: <%= project_fields.text_field :name %>
    <% end %>
  <% end %>

When projects is already an association on Person you can use accepts_nested_attributes_for to define the writer method for you:

  class Person < ActiveRecord::Base
    has_many :projects
    accepts_nested_attributes_for :projects
  end

If you want to destroy any of the associated models through the form, you have to enable it first using the :allow_destroy option for accepts_nested_attributes_for:

  class Person < ActiveRecord::Base
    has_many :projects
    accepts_nested_attributes_for :projects, :allow_destroy => true
  end

This will allow you to specify which models to destroy in the attributes hash by adding a form element for the _destroy parameter with a value that evaluates to true (eg. 1, ‘1’, true, or ‘true’):

  <% form_for @person, :url => { :action => "update" } do |person_form| %>
    ...
    <% person_form.fields_for :projects do |project_fields| %>
      Delete: <%= project_fields.check_box :_destroy %>
    <% end %>
  <% end %>

Returns an file upload input tag tailored for accessing a specified attribute (identified by method) on an object assigned to the template (identified by object). Additional options on the input tag can be passed as a hash with options. These options will be tagged onto the HTML as an HTML element attribute as in the example shown.

Examples

  file_field(:user, :avatar)
  # => <input type="file" id="user_avatar" name="user[avatar]" />

  file_field(:post, :attached, :accept => 'text/html')
  # => <input type="file" id="post_attached" name="post[attached]" />

  file_field(:attachment, :file, :class => 'file_input')
  # => <input type="file" id="attachment_file" name="attachment[file]" class="file_input" />

Creates a form and a scope around a specific model object that is used as a base for questioning about values for the fields.

Rails provides succinct resource-oriented form generation with form_for like this:

  <% form_for @offer do |f| %>
    <%= f.label :version, 'Version' %>:
    <%= f.text_field :version %><br />
    <%= f.label :author, 'Author' %>:
    <%= f.text_field :author %><br />
  <% end %>

There, form_for is able to generate the rest of RESTful form parameters based on introspection on the record, but to understand what it does we need to dig first into the alternative generic usage it is based upon.

Generic form_for

The generic way to call form_for yields a form builder around a model:

  <% form_for :person, :url => { :action => "update" } do |f| %>
    <%= f.error_messages %>
    First name: <%= f.text_field :first_name %><br />
    Last name : <%= f.text_field :last_name %><br />
    Biography : <%= f.text_area :biography %><br />
    Admin?    : <%= f.check_box :admin %><br />
  <% end %>

There, the first argument is a symbol or string with the name of the object the form is about, and also the name of the instance variable the object is stored in.

The form builder acts as a regular form helper that somehow carries the model. Thus, the idea is that

  <%= f.text_field :first_name %>

gets expanded to

  <%= text_field :person, :first_name %>

If the instance variable is not @person you can pass the actual record as the second argument:

  <% form_for :person, person, :url => { :action => "update" } do |f| %>
    ...
  <% end %>

In that case you can think

  <%= f.text_field :first_name %>

gets expanded to

  <%= text_field :person, :first_name, :object => person %>

You can even display error messages of the wrapped model this way:

  <%= f.error_messages %>

In any of its variants, the rightmost argument to form_for is an optional hash of options:

• :url - The URL the form is submitted to. It takes the same fields you pass to url_for or link_to. In particular you may pass here a named route directly as well. Defaults to the current action.
• :html - Optional HTML attributes for the form tag.

Worth noting is that the form_for tag is called in a ERb evaluation block, not an ERb output block. So that‘s <% %>, not <%= %>.

Also note that form_for doesn‘t create an exclusive scope. It‘s still possible to use both the stand-alone FormHelper methods and methods from FormTagHelper. For example:

  <% form_for :person, @person, :url => { :action => "update" } do |f| %>
    First name: <%= f.text_field :first_name %>
    Last name : <%= f.text_field :last_name %>
    Biography : <%= text_area :person, :biography %>
    Admin?    : <%= check_box_tag "person[admin]", @person.company.admin? %>
  <% end %>

This also works for the methods in FormOptionHelper and DateHelper that are designed to work with an object as base, like FormOptionHelper#collection_select and DateHelper#datetime_select.

Resource-oriented style

As we said above, in addition to manually configuring the form_for call, you can rely on automated resource identification, which will use the conventions and named routes of that approach. This is the preferred way to use form_for nowadays.

For example, if @post is an existing record you want to edit

  <% form_for @post do |f| %>
    ...
  <% end %>

is equivalent to something like:

  <% form_for :post, @post, :url => post_path(@post), :html => { :method => :put, :class => "edit_post", :id => "edit_post_45" } do |f| %>
    ...
  <% end %>

And for new records

  <% form_for(Post.new) do |f| %>
    ...
  <% end %>

expands to

  <% form_for :post, Post.new, :url => posts_path, :html => { :class => "new_post", :id => "new_post" } do |f| %>
    ...
  <% end %>

You can also overwrite the individual conventions, like this:

  <% form_for(@post, :url => super_post_path(@post)) do |f| %>
    ...
  <% end %>

And for namespaced routes, like admin_post_url:

  <% form_for([:admin, @post]) do |f| %>
   ...
  <% end %>

Customized form builders

You can also build forms using a customized FormBuilder class. Subclass FormBuilder and override or define some more helpers, then use your custom builder. For example, let‘s say you made a helper to automatically add labels to form inputs.

  <% form_for :person, @person, :url => { :action => "update" }, :builder => LabellingFormBuilder do |f| %>
    <%= f.text_field :first_name %>
    <%= f.text_field :last_name %>
    <%= text_area :person, :biography %>
    <%= check_box_tag "person[admin]", @person.company.admin? %>
  <% end %>

In this case, if you use this:

  <%= render :partial => f %>

The rendered template is people/_labelling_form and the local variable referencing the form builder is called labelling_form.

The custom FormBuilder class is automatically merged with the options of a nested fields_for call, unless it‘s explicitely set.

In many cases you will want to wrap the above in another helper, so you could do something like the following:

  def labelled_form_for(record_or_name_or_array, *args, &proc)
    options = args.extract_options!
    form_for(record_or_name_or_array, *(args << options.merge(:builder => LabellingFormBuilder)), &proc)
  end

If you don‘t need to attach a form to a model instance, then check out FormTagHelper#form_tag.

Returns a hidden input tag tailored for accessing a specified attribute (identified by method) on an object assigned to the template (identified by object). Additional options on the input tag can be passed as a hash with options. These options will be tagged onto the HTML as an HTML element attribute as in the example shown.

Examples

  hidden_field(:signup, :pass_confirm)
  # => <input type="hidden" id="signup_pass_confirm" name="signup[pass_confirm]" value="#{@signup.pass_confirm}" />

  hidden_field(:post, :tag_list)
  # => <input type="hidden" id="post_tag_list" name="post[tag_list]" value="#{@post.tag_list}" />

  hidden_field(:user, :token)
  # => <input type="hidden" id="user_token" name="user[token]" value="#{@user.token}" />

Returns a label tag tailored for labelling an input field for a specified attribute (identified by method) on an object assigned to the template (identified by object). The text of label will default to the attribute name unless a translation is found in the current I18n locale (through views.labels.<modelname>.<attribute>) or you specify it explicitly. Additional options on the label tag can be passed as a hash with options. These options will be tagged onto the HTML as an HTML element attribute as in the example shown, except for the :value option, which is designed to target labels for radio_button tags (where the value is used in the ID of the input tag).

Examples

  label(:post, :title)
  # => <label for="post_title">Title</label>

  You can localize your labels based on model and attribute names.
  For example you can define the following in your locale (e.g. en.yml)

  views:
    labels:
      post:
        body: "Write your entire text here"

  Which then will result in

  label(:post, :body)
  # => <label for="post_body">Write your entire text here</label>

  Localization can also be based purely on the translation of the attribute-name like this:

  activerecord:
    attribute:
      post:
        cost: "Total cost"

  label(:post, :cost)
  # => <label for="post_cost">Total cost</label>

  label(:post, :title, "A short title")
  # => <label for="post_title">A short title</label>

  label(:post, :title, "A short title", :class => "title_label")
  # => <label for="post_title" class="title_label">A short title</label>

  label(:post, :privacy, "Public Post", :value => "public")
  # => <label for="post_privacy_public">Public Post</label>

Returns an input tag of the "password" type tailored for accessing a specified attribute (identified by method) on an object assigned to the template (identified by object). Additional options on the input tag can be passed as a hash with options. These options will be tagged onto the HTML as an HTML element attribute as in the example shown.

Examples

  password_field(:login, :pass, :size => 20)
  # => <input type="text" id="login_pass" name="login[pass]" size="20" value="#{@login.pass}" />

  password_field(:account, :secret, :class => "form_input")
  # => <input type="text" id="account_secret" name="account[secret]" value="#{@account.secret}" class="form_input" />

  password_field(:user, :password, :onchange => "if $('user[password]').length > 30 { alert('Your password needs to be shorter!'); }")
  # => <input type="text" id="user_password" name="user[password]" value="#{@user.password}" onchange = "if $('user[password]').length > 30 { alert('Your password needs to be shorter!'); }"/>

  password_field(:account, :pin, :size => 20, :class => 'form_input')
  # => <input type="text" id="account_pin" name="account[pin]" size="20" value="#{@account.pin}" class="form_input" />

Returns a radio button tag for accessing a specified attribute (identified by method) on an object assigned to the template (identified by object). If the current value of method is tag_value the radio button will be checked.

To force the radio button to be checked pass :checked => true in the options hash. You may pass HTML options there as well.

Examples

  # Let's say that @post.category returns "rails":
  radio_button("post", "category", "rails")
  radio_button("post", "category", "java")
  # => <input type="radio" id="post_category_rails" name="post[category]" value="rails" checked="checked" />
  #    <input type="radio" id="post_category_java" name="post[category]" value="java" />

  radio_button("user", "receive_newsletter", "yes")
  radio_button("user", "receive_newsletter", "no")
  # => <input type="radio" id="user_receive_newsletter_yes" name="user[receive_newsletter]" value="yes" />
  #    <input type="radio" id="user_receive_newsletter_no" name="user[receive_newsletter]" value="no" checked="checked" />

Returns a textarea opening and closing tag set tailored for accessing a specified attribute (identified by method) on an object assigned to the template (identified by object). Additional options on the input tag can be passed as a hash with options.

Examples

  text_area(:post, :body, :cols => 20, :rows => 40)
  # => <textarea cols="20" rows="40" id="post_body" name="post[body]">
  #      #{@post.body}
  #    </textarea>

  text_area(:comment, :text, :size => "20x30")
  # => <textarea cols="20" rows="30" id="comment_text" name="comment[text]">
  #      #{@comment.text}
  #    </textarea>

  text_area(:application, :notes, :cols => 40, :rows => 15, :class => 'app_input')
  # => <textarea cols="40" rows="15" id="application_notes" name="application[notes]" class="app_input">
  #      #{@application.notes}
  #    </textarea>

  text_area(:entry, :body, :size => "20x20", :disabled => 'disabled')
  # => <textarea cols="20" rows="20" id="entry_body" name="entry[body]" disabled="disabled">
  #      #{@entry.body}
  #    </textarea>

Returns an input tag of the "text" type tailored for accessing a specified attribute (identified by method) on an object assigned to the template (identified by object). Additional options on the input tag can be passed as a hash with options. These options will be tagged onto the HTML as an HTML element attribute as in the example shown.

Examples

  text_field(:post, :title, :size => 20)
  # => <input type="text" id="post_title" name="post[title]" size="20" value="#{@post.title}" />

  text_field(:post, :title, :class => "create_input")
  # => <input type="text" id="post_title" name="post[title]" value="#{@post.title}" class="create_input" />

  text_field(:session, :user, :onchange => "if $('session[user]').value == 'admin' { alert('Your login can not be admin!'); }")
  # => <input type="text" id="session_user" name="session[user]" value="#{@session.user}" onchange = "if $('session[user]').value == 'admin' { alert('Your login can not be admin!'); }"/>

  text_field(:snippet, :code, :size => 20, :class => 'code_input')
  # => <input type="text" id="snippet_code" name="snippet[code]" size="20" value="#{@snippet.code}" class="code_input" />