How does Hibernate handle subclass identification?

Hibernate uses the discriminator column for subclass identification, and provides strategies such as union tables, single tables, and class hierarchies: Union tables: Create separate tables for each subclass. Single table: Create a table for all subclasses, distinguished by the discriminator column. Class hierarchy: Use the base class table to store parent class attributes, and use the subclass table to store subclass attributes.

How Hibernate handles subclass identification

Introduction

In object-oriented programming In , subclasses are often used to derive new functionality from a base class. Hibernate provides different strategies for handling object inheritance, including union tables, single tables, and class hierarchies.

Subclass identification

Subclass identification is the process of determining which subclass a given entity is. Hibernate uses the discriminator column to store information that identifies subclasses.

Strategy

Hibernate provides three main strategies to handle subclass identification:

• Union table: Create a separate table for each subclass, with additional columns to store subtype information.
• Single table: Create a table for all subclasses and use the discriminator column to distinguish them.
• Class hierarchy: Use the base class table to store parent class attributes, and use the subclass table to store subclass attributes.

Practical case:

Suppose we have a Person base class and two subclasses Student andEmployee. Here's how to handle subclass identification using a single table strategy:

import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.Table;

@Entity
@Table(name = "Person")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "type", discriminatorType = DiscriminatorType.STRING)
public class Person {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

}

@DiscriminatorValue("Student")
public class Student extends Person {
    private String grade;
}

@DiscriminatorValue("Employee")
public class Employee extends Person {

The above is the detailed content of How does Hibernate handle subclass identification?. For more information, please follow other related articles on the PHP Chinese website!