Hibernate一对多示例
代码结构和使用的jar包
Employee.java(省略get set方法)
package com.orange.demo;
/**
* 员工实体
* 员工和部门的关系是多对一
*/
public class Employee {
private Integer employeeId;
private String employeeName;
private Department department;
}
Department(省略get set方法)
package com.orange.demo;
import java.util.HashSet;
import java.util.Set;
/**
* 部门实体
* 部门和员工的关系是一对多
*/
public class Department {
private Integer departmentId;
private String departmentName;
private Set<Employee> employee = new HashSet<Employee>();
}
Department.hbm.xml（部门类映射文件）
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.orange.demo">
<class name="Department" table="t_department">
<id name="departmentId" column="departmentId">
<generator class="native"></generator>
</id>
<property name="departmentName" column="departmentName" type="string"></property>
<!--
部门和员工是一对多关系
inverse属性:默认为false，表示本方维护关联关系。如果为true，表示本方不维护关联关系。
cascade=delete 删除部门时，同时将该部门的所有员工也删除，和inverse属性无关-->
<set name="employee" inverse="false" cascade="delete">
<!-- 指定需要关联的列 -->
<key column="departmentId"></key>
<!--需要关联的表(类) -->
<one-to-many class="Employee"/>
</set>
</class>
</hibernate-mapping>
Employee.hbm.xml（员工类映射文件）
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.orange.demo">
<class name="Employee" table="t_employee">
<id name="employeeId" column="employeeId">
<generator class="native"></generator>
</id>
<property name="employeeName" column="employeeName" type="string"></property>
<!--相对于员工这一端是 多对一 -->
<many-to-one name="department" class="Department" column="departmentId"></many-to-one>
</class>
</hibernate-mapping>
Test.java
package com.orange.demo;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
public class Test {
private static SessionFactory sessionFactory = null;
static{
Configuration cfg = new Configuration();
cfg.configure("hibernate.cfg.xml"); //在src目录下
sessionFactory = cfg.buildSessionFactory();
}
public static void main(String[] args) {
try {
save();
testGet();
// delete();
} catch (Exception e) {
e.printStackTrace();
}
}
public static void save() throws Exception {
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
Department department1 = new Department();
department1.setDepartmentName("开发部");
Department department2 = new Department();
department2.setDepartmentName("测试部");
Employee employee1 = new Employee();
employee1.setEmployeeName("大橙子");
Employee employee2 = new Employee();
employee2.setEmployeeName("二橙子");
Employee employee3 = new Employee();
employee3.setEmployeeName("小王");
//为员工添加部门
employee1.setDepartment(department1);
employee2.setDepartment(department1);
employee3.setDepartment(department2);
/*//开发部增加两名员工，大橙子和二橙子
department1.getEmployee().add(employee1);
department1.getEmployee().add(employee2);
//测试部增加一名员工，小王
department2.getEmployee().add(employee3);*/
session.save(department1); //需要被依赖的放在前面保存这里是员工需要依赖部门
session.save(department2);
session.save(employee1);
session.save(employee2);
session.save(employee3);
tx.commit();
session.close();
}
public static void testGet() throws Exception {
Session session = sessionFactory.openSession();
// 获取部门，并显示所有员工
System.out.println("---------------------通过部门找员工-----------------------");
Department department = (Department) session.get(Department.class, 1);
System.out.println(department.getDepartmentName()+"有"+department.getEmployee().size()+"员工");
System.out.println(department.getEmployee());//得到的是Employee的set集合，遍历可取出所有员工信息
//获取员工，并显示所在部门
System.out.println("---------------------通过员工找部门-----------------------");
Employee employees = (Employee) session.get(Employee.class, 1);
System.out.println(employees.getEmployeeName()+"在"+employees.getDepartment().getDepartmentName());
session.close();
}
public static void delete() throws Exception{
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
// 删除部门 inverse="true" 如果该部门有员工不能删除，没有才能删除
//inverse="false" 可以删除 ，删除部门后会将员工所属部门设为null
Department department = (Department) session.get(Department.class, 15);
session.delete(department);
tx.commit();
session.close();
}
}
员工和关系选择一种方法即可，结果都是一样的
employee1.setDepartment(department1);
employee2.setDepartment(department1);
employee3.setDepartment(department2);
或者：
department1.getEmployee().add(employee1);
department1.getEmployee().add(employee2);
department2.getEmployee().add(employee3);
删除部门时，这个部门可能会有员工，当inverse=true时，部门不能被删除，只有先将这个部门的员工删除后才能被删除，或者将依赖关系设置成null。
如果设置inverse=false，部门可以被删除 ，删除部门后会将该部门员工部门id设置成null
如果 Department.hbm.xml 中设置cascade="delete" （级联删除）那么删除部门时会将该部门的所有员工删除
hibernate.cfg.xml
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory name="foo"> <!-- 数据库方言 --> <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property> <property name="connection.url">jdbc:mysql://localhost:3306/t1?characterEncoding=UTF-8</property> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="connection.username">root</property> <property name="hibernate.connection.password">123456</property> <!-- 在控制台打印SQL，但不能打印建表语句 --> <property name="hibernate.show_sql">true</property> <!-- 打印SQL是否格式化 false：不格式化 --> <property name="hibernate.format_sql">false</property> <!--自动更新数据库结构 --> <property name="hbm2ddl.auto">update</property> <mapping resource="com/orange/demo/Department.hbm.xml"/> <mapping resource="com/orange/demo/Employee.hbm.xml"/> </session-factory> </hibernate-configuration>