In the world of PHP programming, understanding design patterns can be a game-changer. One such pattern is Class Table Inheritance, a concept that allows us to create a clear and flexible structure for our code.
What is Class Table Inheritance?
Class Table Inheritance is a design pattern that helps us model relationships between classes by creating a table for each class in a hierarchy. This pattern is particularly useful when dealing with complex object-oriented structures and databases. It provides a way to represent a class hierarchy in a relational database while maintaining a clear and understandable structure.
Key Concepts of Class Table Inheritance:
Base Table:
- Represents the common attributes of all classes in the hierarchy.
- Contains columns shared by all subclasses.
Subclass Tables:
- Each subclass has its own table.
- Contains columns specific to that subclass.
Joining Relationships:
- Establishes relationships between tables using primary and foreign keys.
- Enables retrieval of data by joining tables based on these keys.
Example Implementation in PHP:
Let’s consider a simple example where we have a base class Vehicle and two subclasses Car and Motorcycle. Each subclass will have its own unique attributes along with the common attributes inherited from the base class.
Step 1: Create the Base Class
Step 2: Create Subclasses
Step 3: Database Representation
Assuming a relational database, the representation of these classes in tables might look like this:
How Class Table Inheritance Works:
When you want to retrieve information about all vehicles, you can perform a JOIN operation on the vehicles, cars, and motorcycles tables based on the common id column. This allows you to access both the common attributes and the subclass-specific attributes in one query.
Let’s assume we’re working with a MySQL database.
Database Schema:
Performing Join Operations:
1. Retrieve all Vehicles with their Car Details:
2. Retrieve all Vehicles with their Motorcycle Details:
Single Class Queries:
1. Retrieve All Cars:
2. Retrieve All Motorcycles:
3. Retrieve Car Details by Brand:
4. Retrieve Motorcycle Details by Model:
These queries demonstrate how you can perform join operations to retrieve information about vehicles along with their subclass-specific details. Additionally, single class queries allow you to independently get information about cars or motorcycles.
