Question

Single Table Inheritance using ActiveRecord. Since we can use @test = Employee.all and find all the employees created. How does rails do this? Since we only use a User Table. How does it know about employees and retrieve only employees? Rails Magic? Explanation anyone? Thank you in advance.

Base Class : Person (inherits ActiveRecord)
Sub-Class: Employee, Supervisor, Manager (each inherit Person)

So my Person table needs to have a _type and _id field to make the table polymorphic.

My next question is how do I get Employee Associated to the Person table and when you save an employee, how do you get it to actually put in Employee in the person_type field?

Answer 1

To indicate to Ruby on Rails that the
users table needs to support Single
Table Inheritance you need to add a
column named ‘type’ to the users
table. Here is my users table
definition:

CREATE TABLE users ( id INT NOT
NULL AUTO_INCREMENT, user
VARCHAR(15) NOT NULL UNIQUE, pass
VARCHAR(40) NOT NULL, type
VARCHAR(20) NOT NULL, PRIMARY KEY (id) );

In the column named type you
should store the name of the class,
the class type, that should be used
for each user. To mark an certain user
as an admin set his type to
‘Administrator’. By setting a user’s
type to ‘Administrator’ you are giving
him full administrator privileges as
defined in your Administrator model
class.

http://juixe.com/techknow/index.php/2006/06/03/rails-single-table-inheritance/