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Module: ActionView::Helpers::FormHelper

Relationships & Source Files
Extension / Inclusion / Inheritance Descendants
Included In:
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Instance Chain:
Defined in: actionview/lib/action_view/helpers/form_helper.rb

Overview

Form helpers are designed to make working with resources much easier compared to using vanilla HTML.

Typically, a form designed to create or update a resource reflects the identity of the resource in several ways: (i) the url that the form is sent to (the form element's action attribute) should result in a request being routed to the appropriate controller action (with the appropriate :id parameter in the case of an existing resource), (ii) input fields should be named in such a way that in the controller their values appear in the appropriate places within the params hash, and (iii) for an existing record, when the form is initially displayed, input fields corresponding to attributes of the resource should show the current values of those attributes.

In Rails, this is usually achieved by creating the form using #form_for and a number of related helper methods. #form_for generates an appropriate form tag and yields a form builder object that knows the model the form is about. Input fields are created by calling methods defined on the form builder, which means they are able to generate the appropriate names and default values corresponding to the model attributes, as well as convenient IDs, etc. Conventions in the generated field names allow controllers to receive form data nicely structured in params with no effort on your side.

For example, to create a new person you typically set up a new instance of Person in the PeopleController#new action, @person, and in the view template pass that object to #form_for:

<%= form_for @person do |f| %>
  <%= f.label :first_name %>:
  <%= f.text_field :first_name %><br />

  <%= f.label :last_name %>:
  <%= f.text_field :last_name %><br />

  <%= f.submit %>
<% end %>

The HTML generated for this would be (modulus formatting):

<form action="/people" class="new_person" id="new_person" method="post">
  <input name="authenticity_token" type="hidden" value="NrOp5bsjoLRuK8IW5+dQEYjKGUJDe7TQoZVvq95Wteg=" />
  <label for="person_first_name">First name</label>:
  <input id="person_first_name" name="person[first_name]" type="text" /><br />

  <label for="person_last_name">Last name</label>:
  <input id="person_last_name" name="person[last_name]" type="text" /><br />

  <input name="commit" type="submit" value="Create Person" />
</form>

As you see, the HTML reflects knowledge about the resource in several spots, like the path the form should be submitted to, or the names of the input fields.

In particular, thanks to the conventions followed in the generated field names, the controller gets a nested hash params[:person] with the person attributes set in the form. That hash is ready to be passed to Person.create:

if @person = Person.create(params[:person])
  # success
else
  # error handling
end

Interestingly, the exact same view code in the previous example can be used to edit a person. If @person is an existing record with name “John Smith” and ID 256, the code above as is would yield instead:

<form action="/people/256" class="edit_person" id="edit_person_256" method="post">
  <input name="_method" type="hidden" value="patch" />
  <input name="authenticity_token" type="hidden" value="NrOp5bsjoLRuK8IW5+dQEYjKGUJDe7TQoZVvq95Wteg=" />
  <label for="person_first_name">First name</label>:
  <input id="person_first_name" name="person[first_name]" type="text" value="John" /><br />

  <label for="person_last_name">Last name</label>:
  <input id="person_last_name" name="person[last_name]" type="text" value="Smith" /><br />

  <input name="commit" type="submit" value="Update Person" />
</form>

Note that the endpoint, default values, and submit button label are tailored for @person. That works that way because the involved helpers know whether the resource is a new record or not, and generate HTML accordingly.

The controller would receive the form data again in params[:person], ready to be passed to Person#update:

if @person.update(params[:person])
  # success
else
  # error handling
end

That's how you typically work with resources.

Constant Summary

TagHelper - Included

BOOLEAN_ATTRIBUTES, PRE_CONTENT_STRINGS, TAG_PREFIXES

UrlHelper - Included

BUTTON_TAG_METHOD_VERBS

Class Method Summary

Instance Attribute Summary

Instance Method Summary

::ActionView::ModelNaming - Included

#convert_to_model

Converts the given object to an ::ActiveModel compliant one.

#model_name_from_record_or_class

FormTagHelper - Included

#button_tag

Creates a button element that defines a submit button, resetbutton or a generic button which can be used in JavaScript, for example.

#check_box_tag

Creates a check box form input tag.

#color_field_tag

Creates a text field of type “color”.

#date_field_tag

Creates a text field of type “date”.

#datetime_field_tag

Creates a text field of type “datetime”.

#datetime_local_field_tag

Creates a text field of type “datetime-local”.

#email_field_tag

Creates a text field of type “email”.

#field_set_tag

Creates a field set for grouping HTML form elements.

#file_field_tag

Creates a file upload field.

#form_tag

Starts a form tag that points the action to an url configured with url_for_options just like ActionController::Base#url_for.

#hidden_field_tag

Creates a hidden form input field used to transmit data that would be lost due to HTTP's statelessness or data that should be hidden from the user.

#image_submit_tag

Displays an image which when clicked will submit the form.

#label_tag

Creates a label element.

#month_field_tag

Creates a text field of type “month”.

#number_field_tag

Creates a number field.

#password_field_tag

Creates a password field, a masked text field that will hide the users input behind a mask character.

#phone_field_tag
#radio_button_tag

Creates a radio button; use groups of radio buttons named the same to allow users to select from a group of options.

#range_field_tag

Creates a range form element.

#search_field_tag

Creates a text field of type “search”.

#select_tag

Creates a dropdown selection box, or if the :multiple option is set to true, a multiple choice selection box.

#submit_tag

Creates a submit button with the text value as the caption.

#telephone_field_tag

Creates a text field of type “tel”.

#text_area_tag

Creates a text input area; use a textarea for longer text inputs such as blog posts or descriptions.

#text_field_tag

Creates a standard text field; use these text fields to input smaller chunks of text like a username or a search query.

#time_field_tag

Creates a text field of type “time”.

#url_field_tag

Creates a text field of type “url”.

#utf8_enforcer_tag

Creates the hidden UTF8 enforcer tag.

#week_field_tag

Creates a text field of type “week”.

TextHelper - Included

#concat

The preferred method of outputting text in your views is to use the <%= “text” %> eRuby syntax.

#current_cycle

Returns the current cycle string after a cycle has been started.

#cycle

Creates a Cycle object whose to_s method cycles through elements of an array every time it is called.

#excerpt

Extracts an excerpt from text that matches the first instance of phrase.

#highlight

Highlights one or more phrases everywhere in text by inserting it into a :highlighter string.

#pluralize

Attempts to pluralize the singular word unless count is 1.

#reset_cycle

Resets a cycle so that it starts from the first element the next time it is called.

#safe_concat,
#simple_format

Returns text transformed into HTML using simple formatting rules.

#truncate

Truncates a given text after a given :length if text is longer than :length (defaults to 30).

#word_wrap

Wraps the text into lines no longer than line_width width.

SanitizeHelper - Included

#sanitize

Sanitizes HTML input, stripping all tags and attributes that aren't whitelisted.

#sanitize_css

Sanitizes a block of CSS code.

#strip_links

Strips all link tags from html leaving just the link text.

#strip_tags

Strips all HTML tags from html, including comments.

UrlHelper - Included

#button_to

Generates a form containing a single button that submits to the URL created by the set of options.

#current_page?

True if the current request ::URI was generated by the given options.

#link_to

Creates a link tag of the given name using a URL created by the set of options.

#link_to_if

Creates a link tag of the given name using a URL created by the set of options if condition is true, otherwise only the name is returned.

#link_to_unless

Creates a link tag of the given name using a URL created by the set of options unless condition is true, in which case only the name is returned.

#link_to_unless_current

Creates a link tag of the given name using a URL created by the set of options unless the current request ::URI is the same as the links, in which case only the name is returned (or the given block is yielded, if one exists).

#mail_to

Creates a mailto link tag to the specified email_address, which is also used as the name of the link unless name is specified.

TagHelper - Included

#cdata_section

Returns a CDATA section with the given content.

#content_tag

Returns an HTML block tag of type name surrounding the content.

#escape_once

Returns an escaped version of html without affecting existing escaped entities.

#tag

Returns an empty HTML tag of type name which by default is XHTML compliant.

CaptureHelper - Included

#capture

The capture method allows you to extract part of a template into a variable.

#content_for

Calling content_for stores a block of markup in an identifier for later use.

#content_for?

content_for? checks whether any content has been captured yet using content_for.

#provide

The same as content_for but when used with streaming flushes straight back to the layout.

Instance Method Details

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

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(params[:invoice])

wouldn't update the flag.

To prevent this the helper generates an auxiliary hidden field before the very check box. The hidden field has the same name and its attributes mimic an unchecked check box.

This way, 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 parameters extraction gets the last occurrence of any repeated key in the query string, that works for 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. For each item with a checked check box you get an extra ghost item with only that attribute, assigned to “0”.

In that case it is preferable to either use check_box_tag or to use hashes instead of arrays.

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

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

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

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 945

def check_box(object_name, method, options = {}, checked_value = "1", unchecked_value = "0")
  Tags::CheckBox.new(object_name, method, self, checked_value, unchecked_value, options).render
end

#color_field(object_name, method, options = {})

Returns a text_field of type “color”.

color_field("car", "color")
# => <input id="car_color" name="car[color]" type="color" value="#000000" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 974

def color_field(object_name, method, options = {})
  Tags::ColorField.new(object_name, method, self, options).render
end

#date_field(object_name, method, options = {})

Returns a text_field of type “date”.

date_field("user", "born_on")
# => <input id="user_born_on" name="user[born_on]" type="date" />

The default value is generated by trying to call “to_date” on the object's value, which makes it behave as expected for instances of ::DateTime and ::ActiveSupport::TimeWithZone. You can still override that by passing the “value” option explicitly, e.g.

@user.born_on = Date.new(1984, 1, 27)
date_field("user", "born_on", value: "1984-05-12")
# => <input id="user_born_on" name="user[born_on]" type="date" value="1984-05-12" />

You can create values for the “min” and “max” attributes by passing instances of ::Date or ::Time to the options hash.

date_field("user", "born_on", min: Date.today)
# => <input id="user_born_on" name="user[born_on]" type="date" min="2014-05-20" />

Alternatively, you can pass a ::String formatted as an ISO8601 date as the values for “min” and “max.”

date_field("user", "born_on", min: "2014-05-20")
# => <input id="user_born_on" name="user[born_on]" type="date" min="2014-05-20" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1038

def date_field(object_name, method, options = {})
  Tags::DateField.new(object_name, method, self, options).render
end

#datetime_field(object_name, method, options = {})

Returns a text_field of type “datetime”.

datetime_field("user", "born_on")
# => <input id="user_born_on" name="user[born_on]" type="datetime" />

The default value is generated by trying to call strftime with “%Y-%m-%dT%T.%L%z” on the object's value, which makes it behave as expected for instances of ::DateTime and ::ActiveSupport::TimeWithZone.

@user.born_on = Date.new(1984, 1, 12)
datetime_field("user", "born_on")
# => <input id="user_born_on" name="user[born_on]" type="datetime" value="1984-01-12T00:00:00.000+0000" />

You can create values for the “min” and “max” attributes by passing instances of ::Date or ::Time to the options hash.

datetime_field("user", "born_on", min: Date.today)
# => <input id="user_born_on" name="user[born_on]" type="datetime" min="2014-05-20T00:00:00.000+0000" />

Alternatively, you can pass a ::String formatted as an ISO8601 datetime with UTC offset as the values for “min” and “max.”

datetime_field("user", "born_on", min: "2014-05-20T00:00:00+0000")
# => <input id="user_born_on" name="user[born_on]" type="datetime" min="2014-05-20T00:00:00.000+0000" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1096

def datetime_field(object_name, method, options = {})
  Tags::DatetimeField.new(object_name, method, self, options).render
end

#datetime_local_field(object_name, method, options = {})

Returns a text_field of type “datetime-local”.

datetime_local_field("user", "born_on")
# => <input id="user_born_on" name="user[born_on]" type="datetime-local" />

The default value is generated by trying to call strftime with “%Y-%m-%dT%T” on the object's value, which makes it behave as expected for instances of ::DateTime and ::ActiveSupport::TimeWithZone.

@user.born_on = Date.new(1984, 1, 12)
datetime_local_field("user", "born_on")
# => <input id="user_born_on" name="user[born_on]" type="datetime-local" value="1984-01-12T00:00:00" />

You can create values for the “min” and “max” attributes by passing instances of ::Date or ::Time to the options hash.

datetime_local_field("user", "born_on", min: Date.today)
# => <input id="user_born_on" name="user[born_on]" type="datetime-local" min="2014-05-20T00:00:00.000" />

Alternatively, you can pass a ::String formatted as an ISO8601 datetime as the values for “min” and “max.”

datetime_local_field("user", "born_on", min: "2014-05-20T00:00:00")
# => <input id="user_born_on" name="user[born_on]" type="datetime-local" min="2014-05-20T00:00:00.000" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1125

def datetime_local_field(object_name, method, options = {})
  Tags::DatetimeLocalField.new(object_name, method, self, options).render
end

#email_field(object_name, method, options = {})

Returns a text_field of type “email”.

email_field("user", "address")
# => <input id="user_address" name="user[address]" type="email" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1177

def email_field(object_name, method, options = {})
  Tags::EmailField.new(object_name, method, self, options).render
end

#fields_for(record_name, record_object = nil, options = {}, &block)

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.

Although the usage and purpose of fields_for is similar to #form_for's, its method signature is slightly different. Like #form_for, it yields a FormBuilder object associated with a particular model object to a block, and within the block allows methods to be called on the builder to generate fields associated with the model object. Fields may reflect a model object in two ways - how they are named (hence how submitted values appear within the params hash in the controller) and what default values are shown when the form the fields appear in is first displayed. In order for both of these features to be specified independently, both an object name (represented by either a symbol or string) and the object itself can be passed to the method separately -

<%= form_for @person do |person_form| %>
  First name: <%= person_form.text_field :first_name %>
  Last name : <%= person_form.text_field :last_name %>

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

  <%= person_form.submit %>
<% end %>

In this case, the checkbox field will be represented by an HTML input tag with the name attribute permission[admin], and the submitted value will appear in the controller as params[:permission][:admin]. If @person.permission is an existing record with an attribute admin, the initial state of the checkbox when first displayed will reflect the value of @person.permission.admin.

Often this can be simplified by passing just the name of the model object to fields_for -

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

…in which case, if :permission also happens to be the name of an instance variable @permission, the initial state of the input field will reflect the value of that variable's attribute @permission.admin.

Alternatively, you can pass just the model object itself (if the first argument isn't a string or symbol fields_for will realize that the name has been omitted) -

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

and fields_for will derive the required name of the field from the class of the model object, e.g. if @person.permission, is of class Permission, the field will still be named permission[admin].

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 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 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

Note that the projects_attributes= writer method is in fact required for fields_for to correctly identify :projects as a collection, and the correct indices to be set in the form markup.

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

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 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 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 do |person_form| %>
  ...
  <%= person_form.fields_for :projects, @active_projects do |project_fields| %>
    Name: <%= project_fields.text_field :name %>
  <% end %>
  ...
<% 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 do |person_form| %>
  ...
  <%= person_form.fields_for :projects do |project_fields| %>
    Delete: <%= project_fields.check_box :_destroy %>
  <% end %>
  ...
<% end %>

When a collection is used you might want to know the index of each object into the array. For this purpose, the index method is available in the FormBuilder object.

<%= form_for @person do |person_form| %>
  ...
  <%= person_form.fields_for :projects do |project_fields| %>
    Project #<%= project_fields.index %>
    ...
  <% end %>
  ...
<% end %>

Note that fields_for will automatically generate a hidden field to store the ID of the record. There are circumstances where this hidden field is not needed and you can pass include_id: false to prevent fields_for from rendering it automatically.

[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 712

def fields_for(record_name, record_object = nil, options = {}, &block)
  builder = instantiate_builder(record_name, record_object, options)
  capture(builder, &block)
end

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

Returns a 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.

Using this method inside a #form_for block will set the enclosing form's encoding to multipart/form-data.

Options

  • Creates standard HTML attributes for the tag.

  • :disabled - If set to true, the user will not be able to use this input.

  • :multiple - If set to true, *in most updated browsers* the user will be allowed to select multiple files.

  • :accept - If set to one or multiple mime-types, the user will be suggested a filter when choosing a file. You still need to set up model validations.

Examples

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

file_field(:post, :image, :multiple => true)
# => <input type="file" id="post_image" name="post[image]" multiple="true" />

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

file_field(:post, :image, accept: 'image/png,image/gif,image/jpeg')
# => <input type="file" id="post_image" name="post[image]" accept="image/png,image/gif,image/jpeg" />

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

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 857

def file_field(object_name, method, options = {})
  Tags::FileField.new(object_name, method, self, options).render
end

#form_for(record, options = {}, &block)

Creates a form that allows the user to create or update the attributes of a specific model object.

The method can be used in several slightly different ways, depending on how much you wish to rely on ::Rails to infer automatically from the model how the form should be constructed. For a generic model object, a form can be created by passing form_for a string or symbol representing the object we are concerned with:

<%= form_for :person do |f| %>
  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 />
  <%= f.submit %>
<% end %>

The variable f yielded to the block is a FormBuilder object that incorporates the knowledge about the model object represented by :person passed to form_for. Methods defined on the FormBuilder are used to generate fields bound to this model. Thus, for example,

<%= f.text_field :first_name %>

will get expanded to

<%= text_field :person, :first_name %>

which results in an HTML <input> tag whose name attribute is person[first_name]. This means that when the form is submitted, the value entered by the user will be available in the controller as params[:person][:first_name].

For fields generated in this way using the FormBuilder, if :person also happens to be the name of an instance variable @person, the default value of the field shown when the form is initially displayed (e.g. in the situation where you are editing an existing record) will be the value of the corresponding attribute of @person.

The rightmost argument to form_for is an optional hash of options -

  • :url - The URL the form is to be submitted to. This may be represented in the same way as values passed to url_for or link_to. So for example you may use a named route directly. When the model is represented by a string or symbol, as in the example above, if the :url option is not specified, by default the form will be sent back to the current url (We will describe below an alternative resource-oriented usage of form_for in which the URL does not need to be specified explicitly).

  • :namespace - A namespace for your form to ensure uniqueness of id attributes on form elements. The namespace attribute will be prefixed with underscore on the generated HTML id.

  • :method - The method to use when submitting the form, usually either “get” or “post”. If “patch”, “put”, “delete”, or another verb is used, a hidden input with name _method is added to simulate the verb over post.

  • :authenticity_token - Authenticity token to use in the form. Use only if you need to pass custom authenticity token string, or to not add authenticity_token field at all (by passing false). Remote forms may omit the embedded authenticity token by setting config.action_view.embed_authenticity_token_in_remote_forms = false. This is helpful when you're fragment-caching the form. Remote forms get the authenticity token from the meta tag, so embedding is unnecessary unless you support browsers without JavaScript.

  • :remote - If set to true, will allow the Unobtrusive JavaScript drivers to control the submit behavior. By default this behavior is an ajax submit.

  • :enforce_utf8 - If set to false, a hidden input with name utf8 is not output.

  • :html - Optional HTML attributes for the form tag.

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 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]", "1", @person.company.admin? %>
  <%= f.submit %>
<% 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.

#form_for with a model object

In the examples above, the object to be created or edited was represented by a symbol passed to form_for, and we noted that a string can also be used equivalently. It is also possible, however, to pass a model object itself to form_for. For example, if @post is an existing record you wish to edit, you can create the form using

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

This behaves in almost the same way as outlined previously, with a couple of small exceptions. First, the prefix used to name the input elements within the form (hence the key that denotes them in the params hash) is actually derived from the object's class, e.g. params[:post] if the object's class is Post. However, this can be overwritten using the :as option, e.g. -

<%= form_for(@person, as: :client) do |f| %>
  ...
<% end %>

would result in params[:client].

Secondly, the field values shown when the form is initially displayed are taken from the attributes of the object passed to form_for, regardless of whether the object is an instance variable. So, for example, if we had a local variable post representing an existing record,

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

would produce a form with fields whose initial state reflect the current values of the attributes of post.

Resource-oriented style

In the examples just shown, although not indicated explicitly, we still need to use the :url option in order to specify where the form is going to be sent. However, further simplification is possible if the record passed to form_for is a resource, i.e. it corresponds to a set of RESTful routes, e.g. defined using the resources method in config/routes.rb. In this case ::Rails will simply infer the appropriate URL from the record itself. For example,

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

is then equivalent to something like:

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

And for a new record

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

is equivalent to something like:

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

However you can still overwrite individual conventions, such as:

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

You can also set the answer format, like this:

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

For namespaced routes, like admin_post_url:

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

If your resource has associations defined, for example, you want to add comments to the document given that the routes are set correctly:

<%= form_for([@document, @comment]) do |f| %>
 ...
<% end %>

Where @document = {Document.find}(params[:id]) and @comment = {Comment.new}.

Setting the method

You can force the form to use the full array of HTTP verbs by setting

method: (:get|:post|:patch|:put|:delete)

in the options hash. If the verb is not GET or POST, which are natively supported by HTML forms, the form will be set to POST and a hidden input called _method will carry the intended verb for the server to interpret.

Unobtrusive JavaScript

Specifying:

remote: true

in the options hash creates a form that will allow the unobtrusive JavaScript drivers to modify its behavior. The expected default behavior is an XMLHttpRequest in the background instead of the regular POST arrangement, but ultimately the behavior is the choice of the JavaScript driver implementor. Even though it's using JavaScript to serialize the form elements, the form submission will work just like a regular submission as viewed by the receiving side (all elements available in params).

Example:

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

The HTML generated for this would be:

<form action='http://www.example.com' method='post' data-remote='true'>
  <input name='_method' type='hidden' value='patch' />
  ...
</form>

Setting HTML options

You can set data attributes directly by passing in a data hash, but all other HTML options must be wrapped in the HTML key. Example:

<%= form_for(@post, data: { behavior: "autosave" }, html: { name: "go" }) do |f| %>
  ...
<% end %>

The HTML generated for this would be:

<form action='http://www.example.com' method='post' data-behavior='autosave' name='go'>
  <input name='_method' type='hidden' value='patch' />
  ...
</form>

Removing hidden model id's

The form_for method automatically includes the model id as a hidden field in the form. This is used to maintain the correlation between the form data and its associated model. Some ORM systems do not use IDs on nested models so in this case you want to be able to disable the hidden id.

In the following example the Post model has many Comments stored within it in a NoSQL database, thus there is no primary key for comments.

Example:

<%= form_for(@post) do |f| %>
  <%= f.fields_for(:comments, include_id: false) do |cf| %>
    ...
  <% end %>
<% 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, url: { action: "create" }, builder: LabellingFormBuilder do |f| %>
  <%= f.text_field :first_name %>
  <%= f.text_field :last_name %>
  <%= f.text_area :biography %>
  <%= f.check_box :admin %>
  <%= f.submit %>
<% end %>

In this case, if you use this:

<%= render 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 explicitly 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, &block)
  options = args.extract_options!
  form_for(record_or_name_or_array, *(args << options.merge(builder: LabellingFormBuilder)), &block)
end

If you don't need to attach a form to a model instance, then check out FormTagHelper#form_tag.

Form to external resources

When you build forms to external resources sometimes you need to set an authenticity token or just render a form without it, for example when you submit data to a payment gateway number and types of fields could be limited.

To set an authenticity token you need to pass an :authenticity_token parameter

<%= form_for @invoice, url: external_url, authenticity_token: 'external_token' do |f|
  ...
<% end %>

If you don't want to an authenticity token field be rendered at all just pass false:

<%= form_for @invoice, url: external_url, authenticity_token: false do |f|
  ...
<% end %>

Raises:

  • (ArgumentError)
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 422

def form_for(record, options = {}, &block)
  raise ArgumentError, "Missing block" unless block_given?
  html_options = options[:html] ||= {}

  case record
  when String, Symbol
    object_name = record
    object      = nil
  else
    object      = record.is_a?(Array) ? record.last : record
    raise ArgumentError, "First argument in form cannot contain nil or be empty" unless object
    object_name = options[:as] || model_name_from_record_or_class(object).param_key
    apply_form_for_options!(record, object, options)
  end

  html_options[:data]   = options.delete(:data)   if options.has_key?(:data)
  html_options[:remote] = options.delete(:remote) if options.has_key?(:remote)
  html_options[:method] = options.delete(:method) if options.has_key?(:method)
  html_options[:enforce_utf8] = options.delete(:enforce_utf8) if options.has_key?(:enforce_utf8)
  html_options[:authenticity_token] = options.delete(:authenticity_token)

  builder = instantiate_builder(object_name, object, options)
  output  = capture(builder, &block)
  html_options[:multipart] ||= builder.multipart?

  html_options = html_options_for_form(options[:url] || {}, html_options)
  form_tag_with_body(html_options, output)
end

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

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(:, :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}" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 825

def hidden_field(object_name, method, options = {})
  Tags::HiddenField.new(object_name, method, self, options).render
end

#label(object_name, method, content_or_options = nil, options = nil, &block)

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 helpers.label.<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)

helpers:
  label:
    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 (if you are using ::ActiveRecord):

activerecord:
  attributes:
    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>

label(:post, :terms) do
  'Accept <a href="/terms">Terms</a>.'.html_safe
end
# => <label for="post_terms">Accept <a href="/terms">Terms</a>.</label>
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 765

def label(object_name, method, content_or_options = nil, options = nil, &block)
  Tags::Label.new(object_name, method, self, content_or_options, options).render(&block)
end

#month_field(object_name, method, options = {})

Returns a text_field of type “month”.

month_field("user", "born_on")
# => <input id="user_born_on" name="user[born_on]" type="month" />

The default value is generated by trying to call strftime with “%Y-%m” on the object's value, which makes it behave as expected for instances of ::DateTime and ::ActiveSupport::TimeWithZone.

@user.born_on = Date.new(1984, 1, 27)
month_field("user", "born_on")
# => <input id="user_born_on" name="user[born_on]" type="date" value="1984-01" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1142

def month_field(object_name, method, options = {})
  Tags::MonthField.new(object_name, method, self, options).render
end

#number_field(object_name, method, options = {})

Returns an input tag of type “number”.

Options

  • Accepts same options as number_field_tag

[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1185

def number_field(object_name, method, options = {})
  Tags::NumberField.new(object_name, method, self, options).render
end

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

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. For security reasons this field is blank by default; pass in a value via options if this is not desired.

Examples

password_field(:, :pass, size: 20)
# => <input type="password" id="login_pass" name="login[pass]" size="20" />

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

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

password_field(:, :pin, size: 20, class: 'form_input')
# => <input type="password" id="account_pin" name="account[pin]" size="20" class="form_input" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 807

def password_field(object_name, method, options = {})
  Tags::PasswordField.new(object_name, method, self, options).render
end

#phone_field(object_name, method, options = {})

Alias for #telephone_field.

[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1010

alias phone_field telephone_field

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

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.

# 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" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 966

def radio_button(object_name, method, tag_value, options = {})
  Tags::RadioButton.new(object_name, method, self, tag_value, options).render
end

#range_field(object_name, method, options = {})

Returns an input tag of type “range”.

Options

  • Accepts same options as range_field_tag

[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1193

def range_field(object_name, method, options = {})
  Tags::RangeField.new(object_name, method, self, options).render
end

#search_field(object_name, method, options = {})

Returns an input of type “search” for accessing a specified attribute (identified by method) on an object assigned to the template (identified by object_name). Inputs of type “search” may be styled differently by some browsers.

search_field(:user, :name)
# => <input id="user_name" name="user[name]" type="search" />
search_field(:user, :name, autosave: false)
# => <input autosave="false" id="user_name" name="user[name]" type="search" />
search_field(:user, :name, results: 3)
# => <input id="user_name" name="user[name]" results="3" type="search" />
#  Assume request.host returns "www.example.com"
search_field(:user, :name, autosave: true)
# => <input autosave="com.example.www" id="user_name" name="user[name]" results="10" type="search" />
search_field(:user, :name, onsearch: true)
# => <input id="user_name" incremental="true" name="user[name]" onsearch="true" type="search" />
search_field(:user, :name, autosave: false, onsearch: true)
# => <input autosave="false" id="user_name" incremental="true" name="user[name]" onsearch="true" type="search" />
search_field(:user, :name, autosave: true, onsearch: true)
# => <input autosave="com.example.www" id="user_name" incremental="true" name="user[name]" onsearch="true" results="10" type="search" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 997

def search_field(object_name, method, options = {})
  Tags::SearchField.new(object_name, method, self, options).render
end

#telephone_field(object_name, method, options = {}) Also known as: #phone_field

Returns a text_field of type “tel”.

telephone_field("user", "phone")
# => <input id="user_phone" name="user[phone]" type="tel" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1006

def telephone_field(object_name, method, options = {})
  Tags::TelField.new(object_name, method, self, options).render
end

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

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>
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 885

def text_area(object_name, method, options = {})
  Tags::TextArea.new(object_name, method, self, options).render
end

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

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

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 786

def text_field(object_name, method, options = {})
  Tags::TextField.new(object_name, method, self, options).render
end

#time_field(object_name, method, options = {})

Returns a text_field of type “time”.

The default value is generated by trying to call strftime with “%T.%L” on the objects's value. It is still possible to override that by passing the “value” option.

Options

  • Accepts same options as time_field_tag

Example

time_field("task", "started_at")
# => <input id="task_started_at" name="task[started_at]" type="time" />

You can create values for the “min” and “max” attributes by passing instances of ::Date or ::Time to the options hash.

time_field("task", "started_at", min: Time.now)
# => <input id="task_started_at" name="task[started_at]" type="time" min="01:00:00.000" />

Alternatively, you can pass a ::String formatted as an ISO8601 time as the values for “min” and “max.”

time_field("task", "started_at", min: "01:00:00")
# => <input id="task_started_at" name="task[started_at]" type="time" min="01:00:00.000" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1067

def time_field(object_name, method, options = {})
  Tags::TimeField.new(object_name, method, self, options).render
end

#url_field(object_name, method, options = {})

Returns a text_field of type “url”.

url_field("user", "homepage")
# => <input id="user_homepage" name="user[homepage]" type="url" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1168

def url_field(object_name, method, options = {})
  Tags::UrlField.new(object_name, method, self, options).render
end

#week_field(object_name, method, options = {})

Returns a text_field of type “week”.

week_field("user", "born_on")
# => <input id="user_born_on" name="user[born_on]" type="week" />

The default value is generated by trying to call strftime with “%Y-W%W” on the object's value, which makes it behave as expected for instances of ::DateTime and ::ActiveSupport::TimeWithZone.

@user.born_on = Date.new(1984, 5, 12)
week_field("user", "born_on")
# => <input id="user_born_on" name="user[born_on]" type="date" value="1984-W19" />
[ GitHub ]

  
# File 'actionview/lib/action_view/helpers/form_helper.rb', line 1159

def week_field(object_name, method, options = {})
  Tags::WeekField.new(object_name, method, self, options).render
end