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* Form Helpers Cheatsheet

Create forms, check boxes, radio buttons, select lists and more using Rails' built-in form helpers.

Example

Controller

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

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 %>

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>

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" }  ]
                   } }

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.

Multipart form

View

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

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

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"

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

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 %>

Parameters

:customer required

:symbol or "string"

The name of the 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

ActiveRecord model object

If the @instance_variable containing the 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

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.

  • 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:

/customers/1

id=1

{ :id => "1" }

/customers/1?color=red

id=1&color=red

{ :id => "1", :color => "red" }

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

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" }}}

  • 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:

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" }
      ]
    }
 

* Comments

3 MONTHS AGO

Thanks

thanks for this nice article....

ABOUT 1 MONTH AGO

Visual representation not necessary

Thanks for the cheatsheet! And here's some feedback: I think the "Visual representation of params" is unnecessary. The description of "params[]" just above it leaves no doubt about the organization of its content. So that space could be used for something else.

Form-helpers

Pdf_sheet PDF version

 

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