Ruby on Rails/ActiveRecord/acts as


Acts as List will add methods to the ActiveRecord model which provide means for accessing the records as a list.


The acts_as_list directive will add methods to the ActiveRecord object to make each instance act as an element in a list. acts_as_list accepts two configuration options:

  • column : The name of the column used for keeping position (default is position)
  • scope : Restricts what is to be considered a list. Given a symbol, it will attach "_id" (if that hasn’t been already) and use that as the foreign key restriction. It’s also possible to give it an entire string that is interpolated if you need a tighter scope than just a foreign key. Example: acts_as_list :scope => ‘todo_list_id = #{todo_list_id} AND completed = 0’

Instance MethodsEdit

Each instance of a model which has the acts_as_list directive specified will automatically include methods for working with the records as a list:

  • decrement_position
  • first?
  • higher_item
  • in_list?
  • increment_position
  • insert_at
  • last?
  • lower_item
  • move_higher
  • move_lower
  • move_to_bottom
  • move_to_top
  • remove_from_list

Methods which change the position of the item in the list affect the persistent data immediately. For example, a call to move_to_top would be effective immediately.


  class Person < ActiveRecord::Base

Given three people in the database (Joe, Bob and Jane, initially in that order):

 p = Person.find_by_name('Joe')
 => true
 => true
 => false
 => true


The acts_as_tree directive will add methods to the ActiveRecord object to make each instance acts as a node in a tree.