ruby - Rails forms for has_many through association with additional attributes?

Question

How can I generate form fields for a has_many :through association that has additional attributes?

The has_many :through relationship has an additional column called weight.

Here's the migration file for the join table:

create_table :users_widgets do |t|
  t.integer :user_id
  t.integer :widget_id
  t.integer :weight

  t.timestamps
end

The models look like this:

User
  has_many :widgets, :through => :users_widgets,
           :class_name => 'Widget',
           :source => :widget
  has_many :users_widgets
  accepts_nested_attributes_for :widgets # not sure if this is necessary


Widget
  has_many :users, :through => :users_widgets,
           :class_name => 'User',
           :source => :user
  has_many :users_widgets
  accepts_nested_attributes_for :users # not sure if this is necessary


UsersWidget
  belongs_to :user
  belongs_to :widget

For the sake of simplicity, Widget and User only have one field of their own called name, ergo User.first.name and Widget.first.name

Questions:

• How would I append a dropdown selection for Widgets with the corresponding weight to the User create/edit form?

• How can I dynamically add additional Widget forms to Users or User forms to Widgets to easily add or remove these relationships? The nested_form_for gem seems to be the perfect solution but I haven't been able to get it working.

• Apart from the models and the form partials, are there any changes that need to be made to my controller?

---

Quick note.. I'm not interested in creating new Widgets in the User form or new Users in the Widget form, I only want the ability to select from existing objects.

I'm running Rails 3.1 and simple_form 2.0.0dev for generating my forms.

Answer 1

base your question. I made a simple App. source is here: https://github.com/yakjuly/nest_form_example I deployed it to heroku, you can open page: http://glowing-lightning-1954.heroku.com/users/new

answers

1. you want user form can select widget with weight, need do more work.dropdown selection can not satisfy your requirement.

2. I mix "nested_form" in a "bootstrap-rails" plugin, you can add the nested_fields easier

3. in my example, you need add a action calls select, and make WidgetsController#create can responsed_with :js

the code is based simple_form, you can have a try.