hibernate多对多关联映射（二）－－－双向关联

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1.新建工程项目hibernate_many2many_2,在该项目下添加hibernate所需的Jar包和数据库mysql驱动Jar包。

2.编写工具类HibernateUtils和ExportDB,代码如下：

HibernateUtils.java

package com.i51pro.hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtils {
    private static SessionFactory sessionFactory;
    static {
        try {
            Configuration cfg = new Configuration().configure();
            sessionFactory = cfg.buildSessionFactory();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
    public static Session getSession() {
        return sessionFactory.openSession();
    }
    public static void closeSession(Session session) {
        if (session != null) {
            if (session.isOpen()) {
                session.close();
            }
        }
    }
}

ExportDB.java

package com.i51pro.hibernate;
import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
public class ExportDB {
    /**
     * @param args
     */
    public static void main(String[] args) {
        Configuration cfg = new Configuration().configure();
        
        SchemaExport export = new SchemaExport(cfg);
        export.create(true, true);
    }
}

3.编写实体类和映射文件，代码如下：

Role.java

package com.i51pro.hibernate;
import java.util.Set;
public class Role {
    private int id;
    
    private String name;
    private Set users;
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Set getUsers() {
        return users;
    }
    public void setUsers(Set users) {
        this.users = users;
    }
}

User.java

package com.i51pro.hibernate;
import java.util.Set;
public class User {
    private int id;
    
    private String name;
    private Set roles;
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Set getRoles() {
        return roles;
    }
    public void setRoles(Set roles) {
        this.roles = roles;
    }
}

Role.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.i51pro.hibernate.Role" table="t_role">
        <id name="id">
            <generator class="native" />
        </id>
        <property name="name"/>
        <set name="users" table="t_user_role" order-by="userid">
            <key column="roleid" />
            <many-to-many class="com.i51pro.hibernate.User" column="userid" />
        </set>
    </class>
</hibernate-mapping>

User.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.i51pro.hibernate.User" table="t_user">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name"/>
        <set name="roles" table="t_user_role">
            <key column="userid" />
            <many-to-many class="com.i51pro.hibernate.Role" column="roleid" />
        </set>
    </class>
</hibernate-mapping>

4.编写hibernate映射文件，代码如下：

<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_many2many_2</property> 
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">admin</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.show_sql">true</property>
        
        <mapping resource="com/i51pro/hibernate/User.hbm.xml"/>
        <mapping resource="com/i51pro/hibernate/Role.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

5.在项目hibernate_many2many_2下新建SourceFolder,命名为test,在该包下编写测试类Many2Many2Test,进行单元测试，它的代码如下：

package com.i51pro.hibernate;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.Transaction;
import junit.framework.TestCase;
public class One2OneTest extends TestCase {
    public void testSave1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            Transaction tx = session.beginTransaction();
            
            Role role1 = new Role();
            role1.setName("首席执行官");
            session.save(role1);
            
            Role role2 = new Role();
            role2.setName("总裁");
            session.save(role2);
            
            Role role3 = new Role();
            role3.setName("程序员");
            session.save(role3);
            
            User user1 = new User();
            user1.setName("张三");
            Set roles1 = new HashSet();
            roles1.add(role1);
            roles1.add(role2);
            user1.setRoles(roles1);
            
            User user2 = new User();
            user2.setName("李四");
            Set roles2 = new HashSet();
            roles2.add(role2);
            roles2.add(role3);
            user2.setRoles(roles2);
            
            User user3 = new User();
            user3.setName("王二");
            Set roles3 = new HashSet();
            roles3.add(role1);
            roles3.add(role2);
            roles3.add(role3);
            user3.setRoles(roles3);
            
            session.save(user1);
            session.save(user2);
            session.save(user3);
            
            
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }   
        
    public void testLoad() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            Transaction tx = session.beginTransaction();
            
            User user = (User)session.load(User.class, 1);
            System.out.println("user.name=" + user.getName());
            for(Iterator iter = user.getRoles().iterator(); iter.hasNext();) {
                Role role = (Role)iter.next();
                System.out.println("role.name=" + role.getName());
            }
            
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }
    }
    
    public void testLoad2() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            Role role = (Role)session.load(Role.class, 1);
            System.out.println(role.getName());
            for (Iterator iter=role.getUsers().iterator(); iter.hasNext();) {
                User user = (User)iter.next();
                System.out.println(user.getName());
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }       
}

总结：

hibernate多对多关联映射(双向User<---->Role)

映射方法：
  <set name="roles" table="t_user_role">
   <key column="userid"/>
   <many-to-many class="com.bjsxt.hibernate.Role" column="roleid"/>
  </set>
table属性值必须和单向关联中的table属性值一致
<key>中column属性值要与单向关联中的<many-to-many>标签中的column属性值一致
在<many-to-many>中的column属性值要与单向关联中<key>标签的column属性值一致