Ruby on Rails/ActiveRecord/acts as

acts_as_list Acts as List will add methods to the ActiveRecord model which provide means for accessing the records as a list. Directive 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 Methods 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. Example class Person < ActiveRecord::Base acts_as_list end Given three people in the database (Joe, Bob and Jane, initially in that order): p = Person.find_by_name('Joe') p.first? => true p.in_list? => true p.move_to_bottom p.first? => false p.last? => true acts_as_tree The acts_as_tree directive will add methods to the ActiveRecord object to make each instance acts as a node in a tree.