Table Per Concrete Class in Hibernate

Introduction

The Table Per Concrete Class strategy is one of the inheritance mapping strategies in Hibernate that allows for the implementation of inheritance in object-oriented programming. In this approach, each concrete class in the inheritance hierarchy is mapped to its own table. This means that there is no shared table for the parent class and its subclasses. This tutorial will guide you through the implementation of this strategy with detailed explanations and examples.

Understanding the Table Per Concrete Class Strategy

In the Table Per Concrete Class strategy, each subclass has its own table that contains all of its fields, including the fields inherited from its parent class. The parent class does not have a table of its own. This approach can lead to a simpler data model when querying specific subclasses, but it can also lead to data duplication across tables.

This strategy is particularly useful when the subclasses do not share much data with each other, thereby justifying the use of separate tables.

Example Scenario

Let’s consider a simple example where we have a base class Animal and two subclasses Dog and Cat. Each subclass will have its own table in the database.

Entity Classes

First, we will define our entity classes:

Database Schema

Using the above entity classes, Hibernate will create the following database tables:

                CREATE TABLE Animals (
                    id INT PRIMARY KEY AUTO_INCREMENT,
                    name VARCHAR(255)
                );

                CREATE TABLE Dogs (
                    id INT PRIMARY KEY AUTO_INCREMENT,
                    name VARCHAR(255),
                    breed VARCHAR(255)
                );

                CREATE TABLE Cats (
                    id INT PRIMARY KEY AUTO_INCREMENT,
                    name VARCHAR(255),
                    color VARCHAR(255)
                );
                

Advantages and Disadvantages

Advantages

• Each subclass has its own table, which allows for optimized queries.
• Simple design when subclasses do not share much data.

Disadvantages

• Data duplication can occur for fields inherited from the parent class.
• More complex to manage if subclasses share many fields.

Conclusion

The Table Per Concrete Class strategy is a useful inheritance mapping technique in Hibernate, especially when dealing with a clear and distinct hierarchy of classes. By creating separate tables for each concrete class, we can achieve a simple and efficient database design. However, it is essential to evaluate the data structure and access patterns to determine if this strategy is the best fit for your application.