Module | ActionView::Helpers::FormHelper
In: | lib/action_view/helpers/form_helper.rb

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

There are two types of form helpers: those that specifically work with model attributes and those that don‘t. This helper deals with those that work with model attributes; to see an example of form helpers that don‘t work with model attributes, check the ActionView::Helpers::FormTagHelper documentation.

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

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

The HTML generated for this would be:

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

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

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

This example will render the `people/_form` partial, setting a local variable called `form` which references the yielded FormBuilder. The `params` object created when this form is submitted would look like:

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

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

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

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

…will generate the following ERb.

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

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

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

…becomes…

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

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

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

### Methods

check_box fields_for file_field form_for hidden_field label password_field radio_button text_area text_field

### Public Instance 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_attributes(params[:invoice])

wouldn‘t update the flag.

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

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

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

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

#### Examples

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

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

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

fields_for(record_or_name_or_array, *args) {|builder.new(object_name, object, self, 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.

### Generic Examples

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

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

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

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

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

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

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

### Nested Attributes Examples

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

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

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

#### One-to-one

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

      class Person
        def address
          @address
        end

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

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

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

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

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

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

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

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

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

#### One-to-many

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

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

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

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

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

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

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

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

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

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

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

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

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

file_field(object_name, method, options = {})

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

#### Examples

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

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

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

form_for(record_or_name_or_array, *args, &proc)

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

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

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

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

### Generic form_for

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

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

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

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

      <%= f.text_field :first_name %>

gets expanded to

      <%= text_field :person, :first_name %>

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

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

In that case you can think

      <%= f.text_field :first_name %>

gets expanded to

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

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

      <%= f.error_messages %>

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

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

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

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

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

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

### Resource-oriented style

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

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

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

is equivalent to something like:

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

And for new records

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

expands to

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

You can also overwrite the individual conventions, like this:

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

And for namespaced routes, like `admin_post_url`:

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

### Customized form builders

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

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

In this case, if you use this:

      <%= render :partial => f %>

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

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

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

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

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

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}" />

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

Returns a label tag tailored for labelling an input field for a specified attribute (identified by `method`) on an object assigned to the template (identified by `object`). The text of label will default to the attribute name unless you specify it explicitly. Additional options on the label tag can be passed as a hash with `options`. These options will be tagged onto the HTML as an HTML element attribute as in the example shown, 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>

      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>

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.

#### Examples

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

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

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

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

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.

#### Examples

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

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

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>

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

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

[Validate]