Hibernate 配置双向多对多关联

本文解决问题：Hibernate 中配置项目(Project) 员工(Employee)   双向多对多关联

 方案一：直接配置双向多对多

方案二：配置第三个关联类（xml）   将多对多查分开来（形成两个单向多对一关联   完成双向多对多关系）

方案一：直接配置双向多对多

创建Employee持久化类

public class Employee implements java.io.Serializable {

// Fields

private Integer empid;

private String empname;

private Set<Project> projects = new HashSet<Project>();

...其他内容省略

}

创建Project持久化类

public class Project implements java.io.Serializable {
    private Integer proid;
    private String proname;
    private Set<Employee> employees = new HashSet<Employee>();
...其他内容省略
}

分别创建两个小配置文件（hbm.xml文件）

创建Employee.hbm.xml文件

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="cn.happy.daymanymany.Employee" table="EMPLOYEE">
        <id name="empid" type="java.lang.Integer">
            <column name="EMPID"/>
            <generator class="sequence">
              <param name="sequence">SEQ_ID</param>
            </generator>
        </id>
        <property name="empname" type="java.lang.String">
            <column name="EMPNAME" length="32" not-null="true" />
        </property>
        <set name="projects" inverse="true" table="PROEMP">
            <key column="REMPID"/><!-- 表PROEMP的外键REMPID -->
            <many-to-many class="cn.happy.daymanymany.Project" column="RPROID" />
        </set>
    </class>
</hibernate-mapping>

创建Project.hbm.xml文件

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="cn.happy.daymanymany.Project" table="PROJECT">
        <id name="proid" type="java.lang.Integer">
            <column name="PROID"/>
            <generator class="sequence">
              <param name="sequence">SEQ_ID</param>
            </generator>
        </id>
        <property name="proname" type="java.lang.String">
            <column name="PRONAME" length="32" not-null="true" />
        </property>
        <set name="employees" table="PROEMP" cascade="save-update">
            <key column="RPROID" />
            <many-to-many class="cn.happy.daymanymany.Employee" column="REMPID" />
        </set>
    </class>
</hibernate-mapping>

hibernate.cfg.xml主配置文件    （创建大配置文件）

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory name="foo">
     
        <property name="connection.driver_class">oracle.jdbc.OracleDriver</property>
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:HR</property>
        <property name="connection.username">happy</property>
        <property name="connection.password">happy</property>
    
        <property name="dialect">org.hibernate.dialect.OracleDialect</property>
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
        <property name="hbm2ddl.auto">update</property>
        
        <mapping resource="cn/happy/daymanymany/Project.hbm.xml"/>
        <mapping resource="cn/happy/daymanymany/Employee.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

书写测试类

public static SessionFactory factory;
    // 创建Session对象
    public static Session session;
    // 通过代码块赋值
    static {
        factory = new Configuration().configure().buildSessionFactory();
        session = factory.openSession();
    }
    @Test
    public void addTest(){
        Transaction tran = null;
        try {
            tran = 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");
            //指定工程需要的员工
            pro.getEmployees().add(emp);
            //指定员工所属的工程
            emp.getProjects().add(pro);
            session.save(pro);
            // 事务提交
            tran.commit();
            System.out.println("成功");
        } catch (Exception e) {
            e.printStackTrace();
            if (tran != null) {
                tran.rollback();
            }
            throw new RuntimeException("错误");
        } finally {
            // 关闭session
            session.close();
        }
    }
注意：双向多对多，还可以拆成两个多对一       <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>



方案二：配置第三个关联类（xml）   将多对多查分开来（形成两个单向多对一关联   完成双向多对多关系）

（完成与上方同样的功能）分别创建 Employee类、Project类、ProEmp类  ...hbm.xml 

创建Employee持久化类

public class Employee implements java.io.Serializable {
    private Integer empid;
    private String empname;
    private Set<ProEmp> projects = new HashSet<ProEmp>();
 ...其他内容省略  getter() and setter()
}

创建Project持久化类

public class Project implements java.io.Serializable {
    private Integer proid;
    private String proname;
private Set<ProEmp> employees = new HashSet<ProEmp>();
...其他内容省略
}

创建ProEmp持久化类

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

现在来看  拆分后就成了    Employee和Project  分别于ProEmp一对多单向关联的关系了    所以    Employee.hbm.xml和Project.hbm.xml就不必再去关注了。

直接就是ProEmp.hbm.xml 的配置了

创建ProEmp.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.happy.daymanymany">
    <class name="ProEmp" table="PROEMP">
        <id name="id" type="java.lang.Integer">
            <column name="ID"/>  <!-- PROEMP表id字段 -->
            <generator class="sequence">
              <param name="sequence">SEQ_ID</param>
            </generator>
        </id>
        <!-- 配置PROEMP与Employee关联
　　　　　　name：“emp”  指的是PROEMP 类中的相关字段  

　　　　　　　　　　“empid”指的是Employee 类主键列

　　　　 -->
        <many-to-one name="emp" class="Employee">   
          <column name="empid"></column>
        </many-to-one>

　　　　<!-- 配置PROEMP与Employee关联
　　　　　　　　name：“emp”  指的是PROEMP 类中的相关字段  

　　　　　　　　　　  “empid”   指的是Employee 类主键列

　　　　 -->

　　<many-to-one name="pro" class="Project">
　　 <column name="proid"></column> 
 　　</many-to-one> </class> 
　　</hibernate-mapping>

测试方案二：

@Test
    public void many_many_test3(){
        Session session = HibernateUtil.getSession();
        session.beginTransaction();
        
        Employee emp1 = new Employee();
        emp1.setEname("王哲2");
        
        //Project project1 = new Project("1号项目");
        ProEmp p = (ProEmp)session.load(ProEmp.class,new Integer(3));

        ProEmp proemp = new ProEmp();
        proemp.setEmp(emp1);
        proemp.setPro(project1);
        
        session.save(emp1);
        session.save(project1);
        session.save(proemp);
        
        session.getTransaction().commit();
        System.out.println("ok");
    }