Hibernate关联关系之多对多

多对多映射关系

建立多对多单向关联关系

创建Employee类：

 public class Employee {
     private Integer empid;  //员工编号
     private String empname;  //员工姓名
     private Set<Project> projects = new HashSet<Project>();  //植入项目集合
 }

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 package="cn.hibernate.day04mapping.manytomany">
     <!--实体 name=实体端的内容   column=DB端的内容-->
     <class name="Employee" table="EMPLOYEE" schema="liutao">
         <!--和底层数据表对应的主键   业务意义-->
         <id name="empid" column="EMPNO">
            <generator class="native"></generator>
         </id>
         <property name="empname" column="EMPNAME"></property>
         <set name="projects" table="REMPPRO">
             <key column="REMPID"></key>
             <many-to-many class="Project" column="RPROID"></many-to-many>
         </set>
     </class>
 </hibernate-mapping>

属性详解：

name=类中植入的集合名称    table=中间表名称

<key  column=“本类在中间表的外键”></key>

<many-to-many class="映射类" column="映射类在中间表的外键"></many-to-many>

创建Project类 ：

 public class Project {
     private Integer proid;
     private String proname;
 }

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 package="cn.hibernate.day04mapping.manytomany">
     <!--实体 name=实体端的内容   column=DB端的内容-->
     <class name="Project" table="PROJECT" schema="liutao">
         <!--和底层数据表对应的主键   业务意义-->
         <id name="proid" column="PROID">
            <generator class="native"></generator>
         </id>
         <property name="proname" column="PRONAME"></property>
     </class>
 </hibernate-mapping>

测试方法

 //多对多 单向关联  添加一个员工对应多个工程
     @Test
     public void t2(){
         Session session = HibernateUtil.getSession();
         Transaction tx=session.beginTransaction();
         Employee emp1=new Employee();
         emp1.setEmpname("曹梅花");
         Project pro1=new Project();
         pro1.setProname("海淀花园");
         Project pro2=new Project();
         pro2.setProname("三国统治");

         emp1.getProjects().add(pro1);
         emp1.getProjects().add(pro2);

         session.save(emp1);
         session.save(pro1);
         session.save(pro2);
         tx.commit();
         session.close();
     }

表结构

建立多对多双向关联关系

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 package="cn.hibernate.day04mapping.manytomany">
     <!--实体 name=实体端的内容   column=DB端的内容-->
     <class name="Employee" table="EMPLOYEE" schema="liutao">
         <!--和底层数据表对应的主键   业务意义-->
         <id name="empid" column="EMPNO">
            <generator class="native"></generator>
         </id>
         <property name="empname" column="EMPNAME"></property>
         <set name="projects" table="REMPPRO" lazy="true">
             <key column="REMPID"></key>
             <many-to-many class="Project" column="RPROID"></many-to-many>
         </set>
     </class>
 </hibernate-mapping>

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 package="cn.hibernate.day04mapping.manytomany">
     <!--实体 name=实体端的内容   column=DB端的内容-->
     <class name="Project" table="PROJECT" schema="liutao">
         <!--和底层数据表对应的主键   业务意义-->
         <id name="proid" column="PROID">
            <generator class="native"></generator>
         </id>
         <property name="proname" column="PRONAME"></property>
         <set name="employees" table="REMPPRO" lazy="true">
             <key column="RPROID"></key>
             <many-to-many class="Employee" column="REMPID"></many-to-many>
         </set>
     </class>
 </hibernate-mapping>

测试方法

   //多对多双向  查询指定工程参与人员
     //查询员工所属工程
     @Test
     public void t3(){
         Session session = HibernateUtil.getSession();
         Transaction tx=session.beginTransaction();
         Project project = session.load(Project.class, 42);
         System.out.println(project.getProname());
         for (Employee item:project.getEmployees()
              ) {
             System.out.println(item.getEmpname());
         }
         tx.commit();
         session.close();
     }

执行结果

建立多对多双向关联 拆成两个多对一

Employee

 //员工实体
 public class Employee {
     private Integer empid;  //员工编号
     private String empname;  //员工姓名
     private Set<Project> projects = new HashSet<Project>();  //植入项目集合
 }

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 package="cn.hibernate.day04mapping.manytomanydoublebyonetomany">
     <!--实体 name=实体端的内容   column=DB端的内容-->
     <class name="Employee" table="EMPLOYEE" schema="liutao">
         <!--和底层数据表对应的主键   业务意义-->
         <id name="empid" column="EMPNO">
            <generator class="native"></generator>
         </id>
         <property name="empname" column="EMPNAME"></property>
         <set name="projects" table="REMPPRO">
             <key column="REMPID"></key>
             <many-to-many class="Project" column="RPROID"></many-to-many>
         </set>
     </class>
 </-mapping>

ProEmp

 public class ProEmp {
     private Integer id;
     private Project pro;
     private Employee emp;
 }

ProEmp.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 package="cn.hibernate.day04mapping.manytomanydoublebyonetomany">
     <class name="ProEmp" table="PROEMP">
         <id name="id" column="ID">
             <generator class="native"></generator>
         </id>
         <many-to-one name="emp" class="Employee">
             <column name="empid"></column>
         </many-to-one>
         <many-to-one name="pro" class="Project">
             <column name="proid"></column>
         </many-to-one>
     </class>
 </hibernate-mapping>

Project

 public class Project {
     private Integer proid;
     private String proname;
     private Set<Employee> employees=new HashSet<Employee>();
 }

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 package="cn.hibernate.day04mapping.manytomanydoublebyonetomany">
     <!--实体 name=实体端的内容   column=DB端的内容-->
     <class name="Project" table="PROJECT" schema="liutao">
         <!--和底层数据表对应的主键   业务意义-->
         <id name="proid" column="PROID">
            <generator class="native"></generator>
         </id>
         <property name="proname" column="PRONAME"></property>
         <set name="employees" table="REMPPRO" lazy="true">
             <key column="RPROID"></key>
             <many-to-many class="Employee" column="REMPID"></many-to-many>
         </set>
     </class>
 </hibernate-mapping>

单元测试：

 //多对多双向关联  拆分成两个多对一  添加
 @Test
 public void t4(){
     Session session = HibernateUtil.getSession();
     Transaction tx=session.beginTransaction();
     //创建EMP对象
     Employee emp=new Employee();
     emp.setEmpname("李小龙");

     //创建Pro对象
     Project pro=new Project();
     pro.setProname("海淀花园");

     //创建ProEmp对象
     ProEmp proemp=new ProEmp();
     proemp.setEmp(emp);
     proemp.setPro(pro);

     session.save(emp);
     session.save(pro);
     session.save(proemp);
     // 事务提交
     tx.commit();
     session.close();
     System.out.println("成功");
 }