Rails是否正在尝试发送habtm模型联接表的id?

   class CreateUsersRolesJoinTable < ActiveRecord::Migration
    def self.up
      create_table :users_roles, :id => false do |t|
        t.integer :user_id
        t.integer :role_id
      end
    end

    def self.down
      drop_table :users_roles
    end
  end

• http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#M001836
• http://guides.rubyonrails.org/association_basics.html#the-has-and-belongs-to-many-association