Hibernate 、多表关联映射-多对一关系（many-to-one）

Hibernate.cfg.xml:

<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>

Person:

public class Person {

private Integer id;
private String name;
private Department dept;
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 Department getDept() {
return dept;
}
public void setDept(Department dept) {
this.dept = dept;
}

}

Department:

public class Department {

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;
}

}

department.hbm.xml:

<hibernate-mapping package="cn.model">
<class name="Department" table="DEPARTMENT" lazy="true">
<id name="id" column="ID">
<generator class="native"></generator>
</id>
<property name="name" column="NAME" type="java.lang.String" />
<property name="address" column="ADDRESS" type="java.lang.String" />
</class>
</hibernate-mapping>

Person.hbm.xml:

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

使用many-to-one 将Person与Department的实体应射关联起来 DEPT_ID 是Department在Person表中的一个外键，Hibernate会根据Person实体中的dept然后找到对应的实体Department 然后再取得Department 的映射关系；

public void save(){
Session session=null;
Transaction tran=null;
try{
Department dept=new Department();
dept.setName("IT开发部");
Person person=new Person();
person.setName("汤姆");
person.setDept(dept);
session=HibernateSessionFactory.getSession();
tran=session.beginTransaction();
session.save(dept);
session.save(person);
tran.commit();
}catch(Exception e){
if(session!=null){
session.close();
}
}
}

public List<Person> getByName(String name){
Session session=null;
try{
session=HibernateSessionFactory.getSession();
String hql=" from Person where name=:name";
Query query=session.createQuery(hql);
query.setString("name", name);
return query.list();
}catch(Exception e){
if(session!=null){
session.close();
}
}
return null;
}

结果，将取得Person的时候，访问Person的部门属性，会将部门信息关联查询出来：