ruby on rails - Cascade of deletes ActiveRecord -

how can add cascade of deletes remove profile, todolist, , todoitem rows user removed.

user model:

class user < activerecord::base   has_one :profile   has_many :todo_lists   has_many :todo_items, through: :todo_lists, source: :todo_items   validates :username, presence: true   end 

profile model:

class profile < activerecord::base      belongs_to :user       validates :first_name, presence: true      validates :last_name, presence: true       validates :gender, inclusion: %w(male female)       validate :first_and_last      validate :male_sue       def first_and_last       if (first_name.nil? , last_name.nil?)         errors.add(:base, "specify first or last.")       end     end      def male_sue       if (first_name == "sue" , gender == "male")         errors.add(:base, "we prevent male name sue.")       end     end   end 

todolist model:

class todolist < activerecord::base      belongs_to :user     has_many :todo_items, dependent: :destroy     default_scope { order :list_due_date }   end 

todoitem model:

class todoitem < activerecord::base   belongs_to :todo_list    default_scope {order :due_date } end 

thanks, michael.

i guess adding dependent: :destroy do.

#user.rb class user < activerecord::base   has_one :profile, dependent: :destroy   has_many :todo_lists, dependent: :destroy   has_many :todo_items, through: :todo_lists, source: :todo_items, dependent: :destroy   validates :username, presence: true end