Implementing single table inheritance

Relational databases do not support inheritance. If we need to store inheritance in the database, we should somehow support it through code. This code should be efficient, so it should generate as few JOINs as possible. A common solution to this problem was described by Martin Fowler and is named as single table inheritance.

When we use this pattern, we store all the class tree data in a single table and use the type field to determine a model for each row.

As an example, we will implement the single table inheritance for the following class tree:

Car
 |- SportCar
 |- FamilyCar

Getting ready

1. Create a new application by using yiic webapp as described in the official guide.

2. Create and set up a database. Add the following table:

   CREATE TABLE `car` (
       `id` int(10) UNSIGNED NOT NULL AUTO_INCREMENT,
       `name` varchar(255) NOT NULL,
       `type` varchar(100) NOT NULL,
       PRIMARY KEY (`id`)
   );
   
   INSERT INTO `car` (`name`, `type`)
   VALUES ('Ford Focus', 'family')...