Hibernate教程-Hibernate 一对一关系示例(使用 XML)
在 Hibernate 中,有两种方式可以实现一对一的映射:
- 通过
many-to-one
元素(使用unique="true"
属性) - 通过
one-to-one
元素
在这里,我们将通过 one-to-one
元素
来实现一对一的映射。在这种情况下,主表中不会创建外键。
在这个示例中,一个员工可以有一个地址,一个地址也只属于一个员工。这里我们使用双向关联。让我们来看看持久类。
1) 一对一映射的持久类
这里有两个持久类 Employee.java
和 Address.java
。Employee
类包含 Address
类的引用,反之亦然。
Employee.java
package cn.javatiku;
public class Employee {
private int employeeId;
private String name, email;
private Address address;
// setters and getters
}
Address.java
package cn.javatiku;
public class Address {
private int addressId;
private String addressLine1, city, state, country;
private int pincode;
private Employee employee;
// setters and getters
}
2) 持久类的映射文件
两个映射文件分别是 employee.hbm.xml
和 address.hbm.xml
。
employee.hbm.xml
在这个映射文件中,我们在两个映射文件中都使用了 one-to-one
元素来实现一对一映射。
<?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="cn.javatiku.Employee" table="emp212">
<id name="employeeId">
<generator class="increment"></generator>
</id>
<property name="name"></property>
<property name="email"></property>
<one-to-one name="address" cascade="all"></one-to-one>
</class>
</hibernate-mapping>
address.hbm.xml
这是 Address
类的简单映射文件,但重要的是生成器类。这里我们使用了依赖于 Employee
类主键的 foreign
生成器类。
<?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="cn.javatiku.Address" table="address212">
<id name="addressId">
<generator class="foreign">
<param name="property">employee</param>
</generator>
</id>
<property name="addressLine1"></property>
<property name="city"></property>
<property name="state"></property>
<property name="country"></property>
<property name="pincode"></property>
<one-to-one name="employee"></one-to-one>
</class>
</hibernate-mapping>
3) 配置文件
此文件包含有关数据库和映射文件的信息。
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"/>
<mapping resource="address.hbm.xml"/>
</session-factory>
</hibernate-configuration>
4) 存储和获取数据的用户类
Store.java
package cn.javatiku;
import org.hibernate.*;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
public class Store {
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("Ravi Malik");
e1.setEmail("ravi@gmail.com");
Address address1 = new Address();
address1.setAddressLine1("G-21,Lohia nagar");
address1.setCity("Ghaziabad");
address1.setState("UP");
address1.setCountry("India");
address1.setPincode(201301);
e1.setAddress(address1);
address1.setEmployee(e1);
session.persist(e1);
t.commit();
session.close();
System.out.println("success");
}
}
输出
Fetch.java
package cn.javatiku;
import java.util.*;
import javax.persistence.TypedQuery;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
public class Fetch {
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();
TypedQuery query = session.createQuery("from Employee e");
List<Employee> list = query.getResultList();
Iterator<Employee> itr = list.iterator();
while (itr.hasNext()) {
Employee emp = itr.next();
System.out.println(emp.getEmployeeId() + " " + emp.getName() + " " + emp.getEmail());
Address address = emp.getAddress();
System.out.println(address.getAddressLine1() + " " + address.getCity() + " " +
address.getState() + " " + address.getCountry() + " " + address.getPincode());
}
session.close();
System.out.println("success");
}
}