form_for(record_or_name_or_array, *args, &proc) public

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 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 />
  <% end %>

There, the argument is a symbol or string with the name of the object the form is about.

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 %>

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.

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

And for new records

  <%= form_for( do |f| %>
  <% end %>

is equivalent to something like:

  <%= form_for @post, :as => :post, :url => post_path(@post), :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 %>

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

  <%= form_for(@post, :as => :client 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 post given that the routes are set correctly:

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

Where +@document = Document.find(params[:id])+ and +@comment =

Unobtrusive JavaScript


   :remote => true

in the options hash creates a form that will allow the unobtrusive JavaScript drivers to modify its behaviour. The expected default behaviour is an XMLHttpRequest in the background instead of the regular POST arrangement, but ultimately the behaviour 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).


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

The HTML generated for this would be:

  <form action='' method='post' data-remote='true'>
    <div style='margin:0;padding:0;display:inline'>
      <input name='_method' type='hidden' value='put' />

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 %>
    <%= text_area :person, :biography %>
    <%= check_box_tag "person[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 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, &proc)
    options = args.extract_options!
    form_for(record_or_name_or_array, *(args << options.merge(:builder => LabellingFormBuilder)), &proc)

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

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July 22, 2008
19 thanks

Nested resources in form_for

If you like doing things RESTfully and have a model relationship like:

Post_ has many Comments_

Then you can construct a form_for within your view to mirror this relationship when creating comments:

form_for [@post, @comment] do |f|

You also need to make sure your routes reflect this relationship:

map.resources :post, :has_many => [:comments]
August 5, 2008
17 thanks

Multipart form

Don’t forget to add :multipart => true if you have file upload in your form.

<% form_for "user", :html => { :multipart => true } do |f| %>
January 27, 2009 - (>= v2.2.1)
5 thanks

Getting the object in a partial

If you need to get the object for the form inside a partial, and can’t use the instance variable, use the #object method… This is particularly useful when you’re dealing with single-table inheritance subclasses (e.g. MyOtherClass inherits from MyClass) or when you are using the same partial across different controllers.


<% form_for(@my_object) do %>
  <%= render :partial => 'form' %>
  <%= submit_tag 'Create' %>
<% end %>


<% if f.object.class.is_a? MyClass %>
 <%# do something... %>
<% elsif f.object.is_a? MyOtherClass %>
  <%# do something else... %>
<% end %>
September 25, 2008 - (v2.1.0)
3 thanks

Compare old and new form for

Old form for

<% form_for :user, :url => users_path do %>
  <%= render :partial => 'form' %>
  <%= submit_tag 'Create' %>
<% end %>

New form for

<% form_for(@user) do |f| %>
  <%= render :partial => f %>
  <%= submit_tag 'Create' %>
<% end %>
October 8, 2008
3 thanks

Seriously! Do not forget the brackets

thank you source

the form_for([:admin, @user]) must have the [] brackets to avoid errors like “Only get requests are allowed”

<% form_for([:admin, @user]) do |f| %>
<%= render :partial => 'form' %>
<%= submit_tag "Create" %>
<% end %>
September 28, 2008 - (<= v2.1.0)
3 thanks

has_one Nesting in Rails 2.0


map.resources :user, :has_one => [:avatar]


form_for [@user, @avatar], :url => user_avatar_url(@user) do |f|
October 26, 2011
2 thanks

Adding to the URL

If you want to use polymorphic routing for your object but you also need to specify other stuff like an anchor, you can explicitly generate the polymorphic url with extra options:

form_for @candidate,
  :url => polymorphic_path(@candidate, :anchor => 'signup')
November 2, 2008
2 thanks

params hash gets the model id automatically

The params hash gets automatically populated with the id of every model that gets passed to form_for. If we were creating a song inside an existing album:

form_for [@album, @song] do |f| 
  f.submit "Add"

The params hash would be:

params = {"commit"=>"Add", 

So, in the songs_controller you could use this album_id in a before_filter:

before_filter :find_album
def find_album
  @album = Album.find(params[:album_id])

If you only did this:

form_for @song do |f| 

You would get this params hash:

params = {"commit"=>"Add", 
November 4, 2009
2 thanks

Using hidden tags

To use an <input type=“hidden” /> tag, use the following syntax:

<% form_for(@post) do |f| %>
  <%= f.hidden_field :user_id, { :value => } %>
<% end %>
April 9, 2010
2 thanks

The :method goes in the :html option

When using a restful form helper and you want to use a method other than POST, remember to put the :method in the :html option.

e.g. To send a DELETE request instead of the usual POST (with a nested resource thrown in for good measure) use:

<% form_for [@post, @comment], :html => { :method => :delete } do |f| -%>
June 22, 2011
1 thank

:url conflicts with :format

If you are passing both :url and :format, url overwrites the use of format, so you’ll need to pass it in the url like so:

form_for user, :url => user_path(@user, :format => :json)
July 23, 2014 - (v3.2.1)
0 thanks

form_for with namescope and polymorphic path

<%= form_for([:namescope_name, @object], :url => polymorphic_path([:namescope_name, @objectable, @object])) do |form| %>

for the routes.

namescope :admin do

resources :articles do
  resources :comments
resources :photos do
  resources :comments


<%= form_for([:admin, @comment], :url => polymorphic_path([:admin, @commentable, @comment])) do |form| %>

Note : @commentable = find_commentable

June 24, 2010
0 thanks


<div style=“margin:0;padding:0”>

<input name="authenticity_token" type="hidden" value="f755bb0ed134b76c432144748a6d4b7a7ddf2b71" /> 


Helper generates a div element with a hidden input inside. This is a security feature of Rails called cross-site request forgery protection and form helpers generate it for every form whose action is not “get”.

January 16, 2012
0 thanks

form_for with :as routing

The following will not work if your post model is routed with the :as option:


Instead, use the helper with your custom name:

form_for(@post, :url => edit_renamedpost_path(@post))
June 25, 2012 - (<= v2.3.8)
0 thanks

Adding Additional Parameters to form_for

If you want to add additional parameters to the form_for helper, but still want to use one form for both your “create” and your “update” actions, you can add the additional parameters to the :url option, but you need to omit the :controller and :action keys.

form_for(@user, :url => {:param1 => "value1", :param2 => "value2"}) do |f|


form_for([@post, @comment], :url => {:param1 => "value1", :param2 => "value2"}) do |f| 

where param1 and param2 are not :controller or :action

March 7, 2014
0 thanks

form_for with :path route

Similar to danwich’s note, if you specify a route using the :path option

resource :posts, path: 'articles'

then the form_for tag must specify the :url option

form_for(@post), url: post_path(@post)