多对多映射
在平常的工作中，一个员工可能负责多个项目，同时一个项目会由多个员工协同完成。这就是多对多的模型。
所以这篇文章就以上述模型进行演示。
数据库表创建
create table project
(
proid int primary key,
proname varchar(20) not null
);
create table employee
(
empid int primary key,
empname varchar(20)
);
create table proemp
(
rproid int,
rempid int
);
alter table proemp add constraint fk_rproid
foreign key (rproid) references project(proid);
alter table proemp add constraint fk_rempid
foreign key (rempid) references employee(empid);
创建Java Bean
/**
* 员工类
*/
public class Employee {
private int empId;
private String empName;
private Set<Project> projects = new HashSet<>();
// 省略setter/getter
}
/**
* 项目类
*/
public class Project {
private int proId;
private String proName;
private Set<Employee> employees = new HashSet<>();
// 省略setter/getter
}
映射文件
Project.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.whyalwaysmea.hibernate.many2many.Project" table="project">
<id name="proId" column="proid" type="java.lang.Integer">
<generator class="assigned"></generator>
</id>
<property name="proName" type="java.lang.String">
<column name="proname" length="20" not-null="true"></column>
</property>
<!-- 配置多对多关联关系 -->
<set name="employees" table="proemp" cascade="all">
<key column="rproid"></key>
<many-to-many class="com.whyalwaysmea.hibernate.many2many.Employee" column="rempid"></many-to-many>
</set>
</class>
</hibernate-mapping>
Employee.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.whyalwaysmea.hibernate.many2many.Employee" table="employee">
<id name="empId" column="empid" type="java.lang.Integer">
<generator class="assigned"></generator>
</id>
<property name="empName" type="java.lang.String">
<column name="empname" length="20" not-null="true"></column>
</property>
<!-- 配置多对多关联关系 -->
<set name="projects" table="proemp" inverse="true">
<key column="rempid"></key>
<many-to-many class="com.whyalwaysmea.hibernate.many2many.Project" column="rproid"></many-to-many>
</set>
</class>
</hibernate-mapping>
hibernate.cfg.xml就比较简单了，和以前的配置没有什么区别。只是记住加入上面的两个配置文件就可以了
<!-- 多对多映射 -->
<mapping resource="com/whyalwaysmea/hibernate/many2many/Employee.hbm.xml"/>
<mapping resource="com/whyalwaysmea/hibernate/many2many/Project.hbm.xml"/>
简单测试
/**
* 因为在Employee.hbm.xml中设置了inverse="true"，所以将控制权教给Project
* 同时在Project.hbm.xml中设置了cascade="all" 所以保存的时候只用保存Project
*/
@Test
public void saveTest() {
Employee garen = new Employee(1, "盖伦");
Employee luminosity = new Employee(2, "拉克丝");
Project mid = new Project(2, "中路");
Project sup = new Project(3, "辅助");
// 盖伦和拉克丝都在中路
mid.getEmployees().add(garen);
mid.getEmployees().add(luminosity);
// 拉克丝又在辅助
sup.getEmployees().add(luminosity);
session.save(mid);
session.save(sup);
}
@Test
public void findTest() {
Project project = (Project) session.get(Project.class, 2);
System.out.println(project.getProName() + "---" + project.getEmployees());
Employee employee = (Employee) session.get(Employee.class, 1);
System.out.println(employee.getEmpName() + "---" + employee.getProjects());
}
