Polymorphism and forms in Ruby on Rails

Question

I've been full of questions lately, but thanks to this awesome community, I'm learning a ton.

I got all the help I needed with polymorphic associations earlier and now I have a question about tackling forms with polymorphic models. For instance I have Phoneable and User, so when I create my form to register a user, I want to be able to assign a few phone numbers to the user (ie: cell, work, home).

class User < ActiveRecord::Base
  has_many :phones, :as => :phoneable
end

class Phone < ActiveRecord::Base
  belongs_to :phoneable, :polymorphic => true
end

class CreateUsers < ActiveRecord::Migration
  t.column :name, :string
  t.references :phoneable, :polymorphic => true
end

class CreatePhones < ActiveRecord::Migration
  t.column :area_code, :integer
  t.column :number, :integer
  t.column :type, :string
  t.references :phoneable, :polymorphic => true
end

Now when I create my form, I'm getting confused. Normally I would do the following:

- form_for :user, :html => {:multipart => true} do |form|
  %fieldset
    %label{:for => "name"} Name:
    = form.text_field :name
    ##now how do I go about adding a phone number?
    ##typically I'd do this:
    ##%label{:for => "phone"} Phone:
    ##= form.text_field :phone

Using polymorphism, would I just approach the same way, but use fields_for?

- user_form.fields_for :phone do |phone| %>
  %label{for => "area_code"} Area Code:
  = phone.text_field :area_code
  %label{for => "number"} Number:
  = phone.text_field :number

Is this the correct approach in this instance?

Answer 1

Before we go further, I did notice one issue - you do not need the t.references with the has_many side of the association. So you do not need it in the create_user model. What that does is it creates the phonable_id and the phoneable_type columns, you only need that in the polymorphic model.

You are heading down the correct path with the fields_for approach. But in order to get that working, you need to tell the model how to handle those fields. You do that with the accepts_nested_attributes_for class method.

class User < ActiveRecord::Base
  has_many :phones, :as => :phoneable

  accepts_nested_attributes_for :phones
end

and one minor thing, you will need to have the fields_for point to the exact name of the association

- form_for @user do |user_form|
  - user_form.fields_for :phones do |phone|

Instead of

- form_for @user do |user_form|
  - user_form.fields_for :phone do |phone|

and make sure you remove your stray %> erb tag :)

More on accepts_nested_attributes_for: http://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html

I hope this helps!