映射关系

映射是对象到表，映射关系是多个对象的关系映射到多张表的关系！

cascade级联

hibernate的级联是用来说明数据库中两个表的对应关系（一对一，一对多，多对多...，但是多对一一般不需要级联），当对主对象进行操作时，是否对其关联的从对象也进行相应的操作，常见的级联关系有：

• none：对保存，删除，修改主对象时，从对象不做任何操作
• save-update：在保存，更新当前对象时，级联保存，更新附属对象
• delete：在删除当前对象时，级联删除附属对象
• all：所有情况下均进行级联操作，即包含save-update和delete

现在我们来说说，多对一这种关系

项目配置文件

    <!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.driver_class">com.mysql.jdbc.Driver</property>
            <property name="hibernate.connection.url">jdbc:mysql://127.0.0.1/test"</property>
            <property name="hibernate.connection.username">root</property>
            <property name="hibernate.connection.password">root</property>
            <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
            
            <mapping resource="entity/User.hbm.xml" /> -->
            
            <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
            <property name="hibernate.connection.url">jdbc:mysql://127.0.0.1/test</property>
            <property name="hibernate.connection.username">root</property>
            <property name="hibernate.connection.password">root</property>
            <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
            <property name="hibernate.show_sql">true</property>
            <property name="hibernate.hbm2ddl.auto">create</property>
            
            <mapping resource="entity/User.hbm.xml"/>   
            <mapping resource="entity/Group.hbm.xml" /> 
            
        </session-factory>
    </hibernate-configuration>

实体类：

    package entity;
    
    public class Group {
        private int id;
        private String name;
        
        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;
        }
    }

    package entity;
    
    import java.util.Date;
    
    public class User {
        private int id;
        private String userName;
        private String passWd;
        private Date addtime;
        private Group group;
        
        public Date getAddtime() {
            return addtime;
        }
    
        public void setAddtime(Date addtime) {
            this.addtime = addtime;
        }
    
        public User(){}
    
    
    
        public int getId() {
            return id;
        }
    
        public void setId(int id) {
            this.id = id;
        }
    
        public String getUserName() {
            return userName;
        }
    
        public void setUserName(String userName) {
            this.userName = userName;
        }
    
        public String getPassWd() {
            return passWd;
        }
    
        public void setPassWd(String passWd) {
            this.passWd = passWd;
        }
    
        public Group getGroup() {
            return group;
        }
    
        public void setGroup(Group group) {
            this.group = group;
        }
        
        
    }

映射文件：

<?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="entity.Group" table="_group">
        <id name="id">
            <generator class="identity" />
        </id>
        <property name="name" />        
    </class>    
</hibernate-mapping>

<?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="entity.User" >
        <id name="id">
            <!-- 如果是uuid的话，需要id配置为String类型 -->
            <!--  <generator class="uuid"/>-->
            <generator class="identity" />
        </id>
        <property name="userName" />        
        <property name="passWd" />
        <property name="addtime" type="time" />
        <many-to-one name="group" column="group_id" class="entity.Group" />
    </class>    
</hibernate-mapping>

单元测试：

/**
 * 初始化数据写入，测试普通级联写入数据，和数据读取
 */
public void test1(){
    Session session = null;
    
    try {
        session = hibernateUtil.getSession();
        session.beginTransaction();
        
        Group gp1 = new Group();
        gp1.setName("产品组");
        session.save(gp1);
        
        User user1 = new User();
        user1.setUserName("王蕊");
        user1.setPassWd("123456");
        user1.setGroup(gp1);
        user1.setAddtime(new Date());
        
        session.save(user1);
        
        System.out.println("--------------------------------");
        
        User userTmp = (User)session.load(User.class, 1);
        
        System.out.println("用户名："+userTmp.getUserName());
        System.out.println("组名："+userTmp.getGroup().getName());
        
        
        session.getTransaction().commit();
    } catch (Exception e) {
        e.printStackTrace();
        session.getTransaction().rollback();
    }finally{
        hibernateUtil.closeSession(session);
    }       

}