Single Table Polymorphic Inheritance with ActiveRecords

Fri, 23 May 2008 05:27:00 GMT

Implementing a single table polymorphic inheritance in rails is dead easy. Simply do

class Fruit < ActiveRecord::Migration def self.up create_table :persons do |t| t.column :type :string t.column :shape, :string t.timestamps end end def self.down drop_table :fruits end end

or if you a migrating...

class Fruit < ActiveRecord::Migration def self.up add_column :fruits, :type, :string end def self.down remove_column :fruits, :type end end

Now, all you have to do is to create your sub-classes

class Fruit < ActiveRecord::Base def calc_volume ... end end class Apple < Fruit def calc_volume ... end end

Don't forget to put Apple in a separate file by itself apple.rb or else ruby will spit out an unconditional warning if you reference Apple in your code with Fruit::Apple

warning: toplevel constant Fruit referenced by Fruit::Apple

waelchatila.com - ruby tag

Single Table Polymorphic Inheritance with ActiveRecords