使用xml文件的每个具体类的表

如果使用Table Per Concrete类, 则数据库中将有三个彼此无关的表。有两种方法可以将表与每个具体类策略的表进行映射。

• 通过union-subclass元素
• 通过自行为每个班级创建表格

让我们了解我们要映射的层次结构。

让我们看看如何通过union-subclass元素映射此层次结构：

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

  <hibernate-mapping>
  <class name="com.srcmini.mypackage.Employee" table="emp122">
  <id name="id">
  <generator class="increment"></generator>
  </id>
         
  <property name="name"></property>
          
  <union-subclass name="com.srcmini.mypackage.Regular_Employee" table="regemp122">
  <property name="salary"></property>
  <property name="bonus"></property>
  </union-subclass>
          
  <union-subclass name="com.srcmini.mypackage.Contract_Employee" table="contemp122">
  <property name="pay_per_hour"></property>
  <property name="contract_duration"></property>
  </union-subclass>
          
  </class>
          
  </hibernate-mapping>

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;

public class Employee {
private int id;
private String name;

//getters and setters
}

文件：Regular_Employee.java

package com.srcmini.mypackage;

public class Regular_Employee extends Employee{
private float salary;
private int bonus;

//getters and setters
}

文件：Contract_Employee.java

package com.srcmini.mypackage;

public class Contract_Employee extends Employee{
	private float pay_per_hour;
	private String contract_duration;

//getters and setters
}

2）为Persistent类创建映射文件

上面已经针对层次结构讨论了映射。

文件：employee.hbm.xml

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


  <hibernate-mapping>
  <class name="com.srcmini.mypackage.Employee" table="emp122">
  <id name="id">
  <generator class="increment"></generator>
  </id>
         
  <property name="name"></property>
          
  <union-subclass name="com.srcmini.mypackage.Regular_Employee" table="regemp122">
  <property name="salary"></property>
  <property name="bonus"></property>
  </union-subclass>
          
  <union-subclass name="com.srcmini.mypackage.Contract_Employee" table="contemp122">
  <property name="pay_per_hour"></property>
  <property name="contract_duration"></property>
  </union-subclass>
          
  </class>
          
  </hibernate-mapping>

3）在配置文件中添加hbm文件的映射

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

<mapping resource="employee.hbm.xml"/>

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">

<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 resource="employee.hbm.xml"/>
    </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");	
}	
}