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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">
  <div style="display:none">
    <input name="authenticity_token" type="hidden" value="NrOp5bsjoLRuK8IW5+dQEYjKGUJDe7TQoZVvq95Wteg=" />
  </div>
  <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">
  <div style="display:none">
    <input name="_method" type="hidden" value="patch" />
    <input name="authenticity_token" type="hidden" value="NrOp5bsjoLRuK8IW5+dQEYjKGUJDe7TQoZVvq95Wteg=" />
  </div>
  <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.

Methods
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Included Modules
Instance Public methods
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 935
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 964
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 1028
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 1086
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 1115
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 1167
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 ActionView::Helpers::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.

# File actionview/lib/action_view/helpers/form_helper.rb, line 702
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 847
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.

  • :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 ActionView::Helpers::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'>
  <div style='display:none'>
    <input name='_method' type='hidden' value='patch' />
  </div>
  ...
</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'>
  <div style='display:none'>
    <input name='_method' type='hidden' value='patch' />
  </div>
  ...
</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 ActionView::Helpers::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 %>
# File actionview/lib/action_view/helpers/form_helper.rb, line 413
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[: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(: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}" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 815
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>
# File actionview/lib/action_view/helpers/form_helper.rb, line 755
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 1132
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

# File actionview/lib/action_view/helpers/form_helper.rb, line 1175
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(:login, :pass, size: 20)
# => <input type="password" id="login_pass" name="login[pass]" size="20" />

password_field(:account, :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(:account, :pin, size: 20, class: 'form_input')
# => <input type="password" id="account_pin" name="account[pin]" size="20" class="form_input" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 797
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
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 956
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

# File actionview/lib/action_view/helpers/form_helper.rb, line 1183
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 987
def search_field(object_name, method, options = {})
  Tags::SearchField.new(object_name, method, self, options).render
end
telephone_field(object_name, method, options = {})

Returns a #text_field of type “tel”.

telephone_field("user", "phone")
# => <input id="user_phone" name="user[phone]" type="tel" />
Also aliased as: phone_field
# File actionview/lib/action_view/helpers/form_helper.rb, line 996
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>
# File actionview/lib/action_view/helpers/form_helper.rb, line 875
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 776
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 1057
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 1158
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" />
# File actionview/lib/action_view/helpers/form_helper.rb, line 1149
def week_field(object_name, method, options = {})
  Tags::WeekField.new(object_name, method, self, options).render
end