Rails 3.2 - accepts_nested_attributes_for and join models - ruby-on-rails-3

Question

I have the following models: user, role, user_role (user_role is a join model)
I am trying to edit a user's roles using checkboxes on the user#edit page. Here's my attempt, I feel like I'm missing something significant, or taking the wrong approach.
user.rb
has_many :user_roles, dependent: :destroy
has_many :roles, through: :user_roles
attr_accessible :user_roles_attributes
accepts_nested_attributes_for :user_roles, reject_if: lambda { |a| a[:role_id] == 0 }, allow_destroy: true
def has_role?(role_sym)
roles.any? { |r| r.name.underscore.to_sym == role_sym.downcase }
end
def setup_roles!
Role.all.each { |role|
user_roles.build(user_id: id, role_id: role.id) unless has_role?(role.name.to_sym)
}
end
user_role.rb
belongs_to :user
belongs_to :role
delegate :name, to: :role
role.rb
has_many :user_roles
has_many :users, through: :user_role
users_controller.rb
def edit
#user = User.find(params[:id])
#user.setup_roles!
end
def update
#user = User.find(params[:id])
if #user.update_attributes(params[:user])
flash[:notice] = 'User was successfully updated.'
redirect_to edit_user_path(#user)
else
render :edit
end
end
users/edit.html.haml
= form_for #user do |f|
= f.fields_for(:user_roles) do |role_form|
= role_form.check_box :role_id, {}, role_form.object.role_id, 0
= role_form.hidden_field :user_id
= role_form.label :name, role_form.object.name
= f.submit 'Update'

Answer 1

Here is my solution. I received a lot of help from This Post at RubySource. The way the checkbox is setup, it will destroy a UserRole if "unchecked", and only create it when it is "checked" (why the '0', '1' is on that line.)
users_controller.rb
def edit
#user = User.find(params[:id])
#user.setup_roles!
end
user.rb
def has_role?(role_sym)
roles.any? { |r| r.name.underscore.to_sym == role_sym.downcase }
end
def setup_roles!
Role.all.each { |role|
user_roles.build(role: role) unless has_role?(role.name.to_sym)
}
end
users/edit.html.haml
= form_for #user do |f|
= f.fields_for :user_roles do |builder|
= builder.check_box :_destroy, { checked: builder.object.persisted? }, '0', '1'
= builder.label :_destroy, builder.object.role.name
= builder.hidden_field :role_id
= f.submit 'Update'