Hibernate学习3：多对一关联映射

文章目录

1. 1. ER图
2. 2. 实体类（JavaBean）
   1. 2.1. Department.java
   2. 2.2. Employee.java
3. 3. 映射文件
   1. 3.1. Department.hbm.xml
   2. 3.2. Employee.hbm.xml
4. 4. 测试类Many2One

多对一关联关系是Hibernate中很重要的一种关联关系。下面我们举例说明Hibernate中多对一的关联关系。

ER图

部门表有两个字段，id和部门名称name，id是主键；
员工表的主键是id，name指的是员工姓名，department_id是外键。
员工和部门就是多对一的关联关系。

实体类（JavaBean）

Department.java

public class Department {
	private int id;
	private String name;
    //省略get、set方法
}

Employee.java

public class Employee {
	private int id;
	private String name;
	private Department depart; 
    //省略get、set方法
}

映射文件

Department.hbm.xml

<?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/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.zju.domain">
	<class name="Department">
		<id name="id">
			<generator class="native" />
		</id>
		<property name="name"/>
	</class>
</hibernate-mapping>

Employee.hbm.xml

<?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/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.zju.domain">
	<class name="Employee" discriminator-value="0">
		<id name="id">
			<generator class="hilo"/>
		</id>
		<property name="name" unique="true"/>
		<many-to-one name="depart" class="Department" column="depart_id"/>
	</class>	
</hibernate-mapping>

Hibernate提供many-to-one标签来实现多对一关联关系：

<many-to-one name="depart" class="Department" column="depart_id"/>

1. name: 设定待映射的持久化类的属性的名字
2. column: 设定和持久化类的属性对应的表的外键
3. class：设定待映射的持久化类的属性的类型

   测试类Many2One

   public void add() {
   		Session s = null;
   		Transaction tx = null;
   		try {
   			Department depart = new Department();
   			depart.setName("depart name");
   			Employee emp = new Employee();
   			emp.setDepart(depart); //对象模型，建立两个对象的关联关系
   			emp.setName("emp name");	
   			s = HibernateUtil.getSession();
   			tx = s.beginTransaction();
   			s.save(depart);
   			s.save(emp);	
   			tx.commit();
   		} finally {
   			if (s != null)
   				s.close();
   		}
   	}