使用注解的每个子类的表

如前所述, 在每个子类使用表策略的情况下, 表是根据持久性类创建的, 但是使用主键和外键对其进行处理。因此, 该关系中将没有任何重复的列。

我们需要在父类中指定@Inheritance（strategy = InheritanceType.JOINED）, 在子类中指定@PrimaryKeyJoinColumn注释。

让我们看一下我们要映射的类的层次结构。

每个表的表结构如下：

Employee类的表结构

Regular_Employee类的表结构

Contract_Employee类的表结构

使用注释的每个子类类的表的示例

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 = "employee103")
@Inheritance(strategy=InheritanceType.JOINED)

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="regularemployee103")
@PrimaryKeyJoinColumn(name="ID")
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="contractemployee103")
@PrimaryKeyJoinColumn(name="ID")
public class Contract_Employee extends Employee{
	
	@Column(name="pay_per_hour")
	private float pay_per_hour;
	
	@Column(name="contract_duration")
	private String contract_duration;

	//setters and getters
}

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）创建配置文件

打开hibernate.cgf.xml文件, 并添加如下所示的映射资源条目：

<mapping class="com.srcmini.mypackage.Employee"/>
<mapping class="com.srcmini.mypackage.Contract_Employee"/>
<mapping class="com.srcmini.mypackage.Regular_Employee"/>

现在, 配置文件将如下所示：

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。

3）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");  	
	}
}