使用注解的实体表类

如果是“实体表”类, 则按类创建表。因此, 表中没有可为空的值。这种方法的缺点是在子类表中创建了重复的列。

在这里, 我们需要在父类中使用@Inheritance（strategy = InheritanceType.TABLE_PER_CLASS）批注, 在子类中使用@AttributeOverrides批注。

@Inheritance（strategy = InheritanceType.TABLE_PER_CLASS）指定每个具体类策略使用的表。仅应在父类中指定。

@AttributeOverrides定义父类属性将在此类中被覆盖。在表结构中, 父类表列将添加到子类表中。

类层次结构如下：

Employee类的表结构

Regular_Employee类的表结构

Contract_Employee类的表结构

每个具体类别的表格示例

在此示例中, 我们将创建三个类, 并在employee.hbm.xml文件中提供这些类的映射。

1）创建持久类

你需要创建表示继承的持久类。让我们为上述层次结构创建三个类：

文件：Employee.java

package com.srcmini.mypackage;
import javax.persistence.*;

@Entity
@Table(name = "employee102")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)

public class Employee {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
    
@Column(name = "id")
private int id;

@Column(name = "name")
private String name;

//setters and getters
}

文件：Regular_Employee.java

package com.srcmini.mypackage;
import javax.persistence.*;

@Entity
@Table(name="regularemployee102")
@AttributeOverrides({
    @AttributeOverride(name="id", column=@Column(name="id")), @AttributeOverride(name="name", column=@Column(name="name"))
})
public class Regular_Employee extends Employee{
	
@Column(name="salary")	
private float salary;

@Column(name="bonus")	
private int bonus;

//setters and getters
}

文件：Contract_Employee.java

package com.srcmini.mypackage;
import javax.persistence.*;
@Entity
@Table(name="contractemployee102")
@AttributeOverrides({
    @AttributeOverride(name="id", column=@Column(name="id")), @AttributeOverride(name="name", column=@Column(name="name"))
})
public class Contract_Employee extends Employee{
	
	@Column(name="pay_per_hour")
	private float pay_per_hour;
	
	@Column(name="contract_duration")
	private String contract_duration;

	public float getPay_per_hour() {
		return pay_per_hour;
	}
	public void setPay_per_hour(float payPerHour) {
		pay_per_hour = payPerHour;
	}
	public String getContract_duration() {
		return contract_duration;
	}
	public void setContract_duration(String contractDuration) {
		contract_duration = contractDuration;
	}
}

2）在pom.xml文件中添加项目信息和配置。

打开pom.xml文件, 然后单击源。现在, 在<dependencies> …. </ dependencies>标记之间添加以下依赖关系。

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>5.3.1.Final</version>
</dependency>
	
<dependency>
    <groupId>com.oracle</groupId>
    <artifactId>ojdbc14</artifactId>
    <version>10.2.0.4.0</version>
</dependency>

3）在配置文件中添加hbm文件的映射

文件：hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          "-//Hibernate/Hibernate Configuration DTD 5.3//EN"
          "http://hibernate.sourceforge.net/hibernate-configuration-5.3.dtd">

<!-- Generated by MyEclipse Hibernate Tools.                   -->
<hibernate-configuration>
    <session-factory>
        <property name="hbm2ddl.auto">update</property>
        <property name="dialect">org.hibernate.dialect.Oracle9Dialect</property>
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:xe</property>
        <property name="connection.username">system</property>
        <property name="connection.password">jtp</property>
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
 		
 		<mapping class="com.srcmini.mypackage.Employee"/>
 		<mapping class="com.srcmini.mypackage.Contract_Employee"/>
 		<mapping class="com.srcmini.mypackage.Regular_Employee"/>
    </session-factory>
</hibernate-configuration>

定义了hbm2ddl.auto属性, 用于在数据库中创建自动表。

4）创建存储持久对象的类

在此类中, 我们仅将雇员对象存储在数据库中。

文件：StoreData.java

package com.srcmini.mypackage;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

public class StoreData {
 
	public static void main(String[] args) {
	
		StandardServiceRegistry ssr=new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
		Metadata meta=new MetadataSources(ssr).getMetadataBuilder().build();
		
		SessionFactory factory=meta.getSessionFactoryBuilder().build();
		Session session=factory.openSession();
		
		Transaction t=session.beginTransaction();
		
		Employee e1=new Employee();
		e1.setName("Gaurav Chawla");
		
		Regular_Employee e2=new Regular_Employee();
		e2.setName("Vivek Kumar");
		e2.setSalary(50000);
		e2.setBonus(5);
		
		Contract_Employee e3=new Contract_Employee();
		e3.setName("Arjun Kumar");
		e3.setPay_per_hour(1000);
		e3.setContract_duration("15 hours");
		
		session.persist(e1);
		session.persist(e2);
		session.persist(e3);
		
		t.commit();
		session.close();
		System.out.println("success");		
	}
}