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Table of Contents

1. form_for

form_for is used to easily manipulate HTML forms which are based upon ActiveRecord model objects:

<%= form_for(:customer, @customer, :url => { :controller => "customers", :action => "create" }, :html => { :multipart => true, :method => :put }) do |f| %>
  <%= f.text_field :age %> 
  <%= text_field "customer", :age %>
  <%= submit_tag %>
<% end %>

Table 1.1 form_for Parameters

Key	Value	Purpose
:customer required	:symbol or "string"	The name of the ActiveRecord model object for all the fields in the form. All input fields will be prefixed with this. Rails will also look for an @instance_variable with the same name which should contain an instance of an existing or new ActiveRecord model object
@customer optional	Object	If the @instance_variable containing the ActiveRecord model object is named differently, you can pass a variable containing the actual model object here
:url optional	"string" or {hash}	The URL to post the form to. Can take an explicit url as a string, or a hash in the same format as url_for
:html optional	{hash}	A {hash} of HTML attributes which will be added to the HTML <form> tag.
:method optional	:symbol	Pass as part of the {hash} of HTML attributes. Can be :put, :post, :get or :delete

2. Parsing form data

When a form is submitted to a Rails application, the parameters are automatically translated by Rails into the params object which is accessible as a hash structure.

2.1. Simple query strings

Key/value pairs of your form’s input fields are stored simply as key/value pairs in the params hash, such as the id which is extracted by routing from the URL:

URL	Parameters	Hash constructed
/customers/1	id=1	{ :id => "1" }
/customers/1?color=red	id=1&color=red	{ :id => "1", :color => "red" }

2.2. Nesting

Square brackets [] are used to build more complex, nested structures:

Field helper	Parameters	Hash constructed
text_field :user, :name	user[name]=David	{ :user => { :name => "David" }
text_field "user[address]", :city	user[address][city]=London	{ :user => { :address => { :city => "London" }}}
text_field "user[address]", :street	user[address][street]=Road	{ :user => { :address => { :street => "Road" }}}

2.3. Multiple records

Using empty square brackets [] after the name of a model object, such as address[], will insert the id of the record you are editing into the input field, useful for editing multiple records on one form:

Field helper	Parameters	Hash constructed
text_field "address[]", :country	address[4][country]=England	{ :address => { 4 => { :country => "England" }}}
text_field "address[]", :town	address[4][town]=London	{ :address => { 4 => { :town => "London" }}}

If the record is new and has no id, then upon submitting the form, Rails will convert the fields into an array of hashes in order of appearance.

text_field "address[]", :country 
text_field "address[]", :town
text_field "address[]", :country
text_field "address[]", :town

{ :address => [
    { :country => "England", :town => "London" },
    { :country => "Australia", :town => "Sydney" }
  ]
}

3. Example

3.1. Controller

def new
  @customer = Customer.new
  3.times do 
    @customer.addresses.build        
  end
end

3.2. View

<% form_for(@customer) do |f| %>
  <%= f.text_field :name %>
  <%= f.text_field :email %>
  <% @customer.addresses.each do |address| %>
    <% fields_for "customer[addresses][]", address do |fields| %>
      <%= fields.text_field :number %>
          <%= fields.text_field :street %>
  <% end %>
<% end %>

3.3. HTML

<form id="new_customer" class="new_customer" method="post" action="/customers">
<input type="text" size="30" name="customer[name]"/>
<input type="text" size="30" name="customer[email]"/>
<input type="text" size="30" name="customer[addresses][][number]"/>
<input type="text" size="30" name="customer[addresses][][street]"/>
<input type="text" size="30" name="customer[addresses][][number]"/>
<input type="text" size="30" name="customer[addresses][][street]"/>
<input type="text" size="30" name="customer[addresses][][number]"/>
<input type="text" size="30" name="customer[addresses][][street]"/>
<input type="submit" value="Create" name="commit"/>
</form>

3.4. params

params = {
  "customer" => { "name"=>"David Pettifer",
                  "email"=>"david.p@dizzy.co.uk",
                  "addresses"=> [
                    { "number"=>"31", "street"=>"High" },
                    { "number"=>"22", "street"=>"Brook" },
                    { "number"=>"16", "street"=>"Kents" }  ]
               } }

4. fields_for

fields_for creates a scope around a specific model object like form_for, but doesn’t create the form tags themselves, making fields_for suitable for specifying additional model objects in the same form. See the example.

5. RESTful form_for

When standard routes are used in a RESTful context, Rails will reflect upon the object passed to it and automatically build a form with the relevant RESTful URL depending on whether the form is wrapping a new record (create) or an existing record (update). Nested routes will require you to be more verbose. Standard routes

Standard routes	new record?	method	URL
form_for(@customer)	yes	POST	/customers
form_for(@customer)	no	PUT	/customers/1

Nested routes	new record?	method	URL
form_for(@address, :url => customer_addresses_path(@customer))	yes	POST	/customers/1/addresses
form_for(@address, :url => customer_addresses_path(@customer))	no	PUT	/customers/1/addresses/24

6. Input field helpers

f.error_messages_for
f.check_box :terms, { :class => 'check' }, "yes", "no"
f.file_field :image
f.hidden_field :id
f.label :customer, "Text for label"
f.password_field :password
f.radio_button :language, "French"
f.text_area :comment, :size => "20x30", :disabled => "disabled"
f.text_field :age, :size => "20", :class => "age_box"

7. Multipart form

7.1. View

<% form_for(@customer, :html => { :multipart => true }) do |f| %>
  <%= f.file_field :image_file %>
<%= submit_tag %>
<% end %>

7.2. Model

class Customer < ActiveRecord::Base
  def image_file=(uploaded_data)
    self.filename     = uploaded_data.original_filename
    self.image_data   = uploaded_data.read
    self.size         = uploaded_data.size
    self.content_type = uploaded_data.content_type        
  end
end