Module: ActionView::Helpers::FormHelper

Included in:
ActionView::Helpers
Defined in:
lib/action_view/helpers/form_helper.rb

Overview

Form helpers are designed to make working with models much easier compared to using just standard HTML elements by providing a set of methods for creating forms based on your models. This helper generates the HTML for forms, providing a method for each sort of input (e.g., text, password, select, and so on). When the form is submitted (i.e., when the user hits the submit button or form.submit is called via JavaScript), the form inputs will be bundled into the params object and passed back to the controller.

There are two types of form helpers: those that specifically work with model attributes and those that don't. This helper deals with those that work with model attributes; to see an example of form helpers that don't work with model attributes, check the ActionView::Helpers::FormTagHelper documentation.

The core method of this helper, form_for, gives you the ability to create a form for a model instance; for example, let's say that you have a model Person and want to create a new instance of it:

# Note: a @person variable will have been created in the controller.
# For example: @person = Person.new
<% form_for :person, @person, :url => { :action => "create" } do |f| %>
  <%= f.text_field :first_name %>
  <%= f.text_field :last_name %>
  <%= submit_tag 'Create' %>
<% end %>

The HTML generated for this would be:

<form action="/persons/create" method="post">
  <input id="person_first_name" name="person[first_name]" size="30" type="text" />
  <input id="person_last_name" name="person[last_name]" size="30" type="text" />
  <input name="commit" type="submit" value="Create" />
</form>

If you are using a partial for your form fields, you can use this shortcut:

<% form_for :person, @person, :url => { :action => "create" } do |f| %>
  <%= render :partial => f %>
  <%= submit_tag 'Create' %>
<% end %>

This example will render the people/_form partial, setting a local variable called form which references the yielded FormBuilder.

The params object created when this form is submitted would look like:

{"action"=>"create", "controller"=>"persons", "person"=>{"first_name"=>"William", "last_name"=>"Smith"}}

The params hash has a nested person value, which can therefore be accessed with params[:person] in the controller. If were editing/updating an instance (e.g., Person.find(1) rather than Person.new in the controller), the objects attribute values are filled into the form (e.g., the person_first_name field would have that person's first name in it).

If the object name contains square brackets the id for the object will be inserted. For example:

<%= text_field "person[]", "name" %>

…will generate the following ERb.

<input type="text" id="person_<%= @person.id %>_name" name="person[<%= @person.id %>][name]" value="<%= @person.name %>" />

If the helper is being used to generate a repetitive sequence of similar form elements, for example in a partial used by render_collection_of_partials, the index option may come in handy. Example:

<%= text_field "person", "name", "index" => 1 %>

…becomes…

<input type="text" id="person_1_name" name="person[1][name]" value="<%= @person.name %>" />

An index option may also be passed to form_for and fields_for. This automatically applies the index to all the nested fields.

There are also methods for helping to build form tags in classes/ActionView/Helpers/FormOptionsHelper.html, classes/ActionView/Helpers/DateHelper.html, and classes/ActionView/Helpers/ActiveRecordHelper.html

Instance Method Summary collapse

Instance Method Details

#apply_form_for_options!(object_or_array, options) ⇒ Object

:nodoc:


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# File 'lib/action_view/helpers/form_helper.rb', line 257

def apply_form_for_options!(object_or_array, options) #:nodoc:
  object = object_or_array.is_a?(Array) ? object_or_array.last : object_or_array

  html_options =
    if object.respond_to?(:new_record?) && object.new_record?
      { :class  => dom_class(object, :new),  :id => dom_id(object), :method => :post }
    else
      { :class  => dom_class(object, :edit), :id => dom_id(object, :edit), :method => :put }
    end

  options[:html] ||= {}
  options[:html].reverse_merge!(html_options)
  options[:url] ||= polymorphic_path(object_or_array)
end

#check_box(object_name, method, options = {}, checked_value = "1", unchecked_value = "0") ⇒ Object

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" />

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# File 'lib/action_view/helpers/form_helper.rb', line 495

def check_box(object_name, method, options = {}, checked_value = "1", unchecked_value = "0")
  InstanceTag.new(object_name, method, self, options.delete(:object)).to_check_box_tag(options, checked_value, unchecked_value)
end

#fields_for(record_or_name_or_array, *args) {|builder.new(object_name, object, self, options, block)| ... } ⇒ Object

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:

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.

Yields:

  • (builder.new(object_name, object, self, options, block))

Raises:

  • (ArgumentError)

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# File 'lib/action_view/helpers/form_helper.rb', line 299

def fields_for(record_or_name_or_array, *args, &block)
  raise ArgumentError, "Missing block" unless block_given?
  options = args.extract_options!

  case record_or_name_or_array
  when String, Symbol
    object_name = record_or_name_or_array
    object = args.first
  else
    object = record_or_name_or_array
    object_name = ActionController::RecordIdentifier.singular_class_name(object)
  end

  builder = options[:builder] || ActionView::Base.default_form_builder
  yield builder.new(object_name, object, self, options, block)
end

#file_field(object_name, method, options = {}) ⇒ Object

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" />

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# File 'lib/action_view/helpers/form_helper.rb', line 412

def file_field(object_name, method, options = {})
  InstanceTag.new(object_name, method, self, options.delete(:object)).to_input_field_tag("file", options)
end

#form_for(record_or_name_or_array, *args, &proc) ⇒ Object

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.

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.

Raises:

  • (ArgumentError)

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# File 'lib/action_view/helpers/form_helper.rb', line 232

def form_for(record_or_name_or_array, *args, &proc)
  raise ArgumentError, "Missing block" unless block_given?

  options = args.extract_options!

  case record_or_name_or_array
  when String, Symbol
    object_name = record_or_name_or_array
  when Array
    object = record_or_name_or_array.last
    object_name = ActionController::RecordIdentifier.singular_class_name(object)
    apply_form_for_options!(record_or_name_or_array, options)
    args.unshift object
  else
    object = record_or_name_or_array
    object_name = ActionController::RecordIdentifier.singular_class_name(object)
    apply_form_for_options!([object], options)
    args.unshift object
  end

  concat(form_tag(options.delete(:url) || {}, options.delete(:html) || {}))
  fields_for(object_name, *(args << options), &proc)
  concat('</form>')
end

#hidden_field(object_name, method, options = {}) ⇒ Object

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}" />

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# File 'lib/action_view/helpers/form_helper.rb', line 393

def hidden_field(object_name, method, options = {})
  InstanceTag.new(object_name, method, self, options.delete(:object)).to_input_field_tag("hidden", options)
end

#label(object_name, method, text = nil, options = {}) ⇒ Object

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 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.

Examples

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

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# File 'lib/action_view/helpers/form_helper.rb', line 331

def label(object_name, method, text = nil, options = {})
  InstanceTag.new(object_name, method, self, options.delete(:object)).to_label_tag(text, options)
end

#password_field(object_name, method, options = {}) ⇒ Object

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" />

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# File 'lib/action_view/helpers/form_helper.rb', line 375

def password_field(object_name, method, options = {})
  InstanceTag.new(object_name, method, self, options.delete(:object)).to_input_field_tag("password", options)
end

#radio_button(object_name, method, tag_value, options = {}) ⇒ Object

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. Additional options on the input tag can be passed as a hash with options.

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" />

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# File 'lib/action_view/helpers/form_helper.rb', line 515

def radio_button(object_name, method, tag_value, options = {})
  InstanceTag.new(object_name, method, self, options.delete(:object)).to_radio_button_tag(tag_value, options)
end

#text_area(object_name, method, options = {}) ⇒ Object

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>

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# File 'lib/action_view/helpers/form_helper.rb', line 440

def text_area(object_name, method, options = {})
  InstanceTag.new(object_name, method, self, options.delete(:object)).to_text_area_tag(options)
end

#text_field(object_name, method, options = {}) ⇒ Object

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" />

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# File 'lib/action_view/helpers/form_helper.rb', line 353

def text_field(object_name, method, options = {})
  InstanceTag.new(object_name, method, self, options.delete(:object)).to_input_field_tag("text", options)
end