whats wrong with my collection_select in my sign up view page - ruby-on-rails

Question

I am newbie to rails ,
I am using devise from ryan bates video tutorial , and , i am stuck at one point
I have created user , role relationship
and in the sign up page , i need to provide select option group for existing roles ,
in my sign up view page i am writing
<%= collection_select(:user,:roles,Role.find(:all),:id,:name) %>
i dont precisely understand collection_select method , kindly help what i might be doing wrong
my models 1 : user.rb
class User < ActiveRecord::Base
has_and_belongs_to_many :roles
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable
attr_accessible :email, :password, :password_confirmation, :remember_me , :roles
has_and_belongs_to_many :roles
def role?(role)
return !!self.roles.find_by_name(role.to_s.camelize)
end
end
my model 2 : role.rb
class Role < ActiveRecord::Base
attr_accessible :name
has_and_belongs_to_many :users
end
my user migration file
class DeviseCreateUsers < ActiveRecord::Migration
def change
create_table(:users) do |t|
## Database authenticatable
t.string :email, :null => false, :default => ""
t.string :encrypted_password, :null => false, :default => ""
## Recoverable
t.string :reset_password_token
t.datetime :reset_password_sent_at
## Rememberable
t.datetime :remember_created_at
## Trackable
t.integer :sign_in_count, :default => 0
t.datetime :current_sign_in_at
t.datetime :last_sign_in_at
t.string :current_sign_in_ip
t.string :last_sign_in_ip
t.timestamps
end
add_index :users, :email, :unique => true
add_index :users, :reset_password_token, :unique => true
end
end
my role migration file
class CreateRoles < ActiveRecord::Migration
def change
create_table :roles do |t|
t.string :name
t.timestamps
end
end
end
my join table migration file
class UsersHaveAndBelongToManyRoles < ActiveRecord::Migration
def up
create_table :roles_users, :id => false do |t|
t.references :role, :user
end
end
def down
drop_table :roles_users
end
end
the ERROR COMING is
undefined method `each' for "2":String
2 being the id of the role selected

Answer 1

In a has_and_belongs_to_many relationship like you have between User and Role, there is no role_id on the User object.
The second parameter of the collection_select is the attribute you're updating with the selection(s), in your case it's not role_id, it's role_ids and seeing as it's a has_and_belongs_to_many relationship you probably want to allow the user to select multiple options, so try something like this:
<%= collection_select(:user, :role_ids, Role.all, :id, :name, {}, { selected: #user.role_ids, multiple: true }) %>
If you attach it to a form_for on your #user object you can use:
<%= f.collection_select(:role_ids, Role.all, :id, :name, {}, multiple: true) %>