Rails 3.2 - accepts_nested_attributes_for and join models

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'