Hibernate 多表关联映射- 一对多关系映射（one-to-many）

Hibernage.cfg.xml:

<hibernate-configuration>
    <session-factory name="sessionFactory">
    	<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    	<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    	<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/spring?useUnicode=true&characterEncoding=UTF-8</property>
    	<property name="hibernate.connection.username">root</property>
    	<property name="hibernate.connection.password"></property>
    	<property name="hibernate.show_sql">true</property>
    	<property name="hibernate.format_sql">true</property>
    	<property name="hibernate.hbm2ddl.auto">update</property>
    	<mapping resource="cn/hbm/Person.hbm.xml" />
    	<mapping resource="cn/hbm/Department.hbm.xml" />
    </session-factory>
</hibernate-configuration>

Person:

public class Person {
	private Integer id;
	private String name;
	
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

hbm.xml:

<hibernate-mapping package="cn.model">
	<class name="Person" table="PERSON">
		<id name="id" column="ID">
			<generator class="native"></generator>
		</id>
		<property name="name" column="NAME" type="java.lang.String" />
	</class> 
</hibernate-mapping>

Department:

public class Department {

	private Integer id;
	private String name;
	private Set<Person> persons;
	
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Set<Person> getPersons() {
		return persons;
	}
	public void setPersons(Set<Person> persons) {
		this.persons = persons;
	}

}

hbm.xml:

<hibernate-mapping package="cn.model">
	<class name="Department" table="DEPARTMENT">
		<id name="id" column="ID">
			<generator class="native"></generator>
		</id>
		<property name="name" column="NAME" type="java.lang.String" />
		 <set name="persons">
			<key column="DEPT_ID" />
			<one-to-many class="Person" />
		</set>
	</class> 
</hibernate-mapping>

在Department实体中有一个Set<> 集合用来存储该部门下的所有员工，在hbm.xml 可以使用Set实现映射关系，one-to-many中需要指定Set中存储的对象来自哪个实体；并且通过Key中的列名来进行关连映射操作。

添加数据：

public void save(){
		Session session=null;
		Transaction tran=null;
		try{
			Department dept=new Department();
			dept.setName("IT开发部");
			
			Person person1=new Person();
			person1.setName("汤姆克路斯");
			person1.setDept(dept);
			
			Person person2=new Person();
			person2.setName("大为史密斯");
			person2.setDept(dept);
			
			// 或者(结果一样，但是Hibenate的处理流程完全不一样)
			//Person person1=new Person();
			//person1.setDept(dept);
			//Person person2=new Person();
			//person2.setName("大为史密斯");
			//Set<Person> sets=new HashSet();
			//sets.add(person1);
			//sets.add(person2);
			//Department dept=new Department();
			//dept.setName("IT开发部");
			//dept.setPersons(sets);
			
			session=HibernateSessionFactory.getSession();
			tran=session.beginTransaction();
			session.save(dept);
			session.save(person1);
			session.save(person2);
			tran.commit();
		}catch(Exception e){
			if(session!=null){
				session.close();
			}
		}
	}

获取部门：

public Department getDepartmentById(Serializable id){
		Session session=null;
		try{
			session=HibernateSessionFactory.getSession();
			Department dept=(Department)session.get(Department.class, id);
			//关于延迟加载（lazy）和强制加载（Hibernate.initialize(Object proxy) ) 等
			//在配置文件里面可以用lazy=true，在程序里面可以用强制加载的方法Hibernate.initialize(Object proxy) 方法强制加载这样就相当于动态改变为lazy=false。
			Hibernate.initialize(dept.getPersons());
			return dept;
		}catch(Exception e){
			if(session!=null){
				session.close();
			}
		}
		return null;
	}

测试：

@Test
	public void testDeptList(){
		Demo demo=new Demo();
		Department dept=demo.getDepartmentById(1);
			System.out.println("部门："+dept.getName());
			System.out.println("员工有：");
			for(Person per : dept.getPersons()){
				System.out.println(per.getName());
			}
	}

结果 ：