你Group实体类的id是设置的自动增长,且配置的是级联保存吧。给“经理”组添加第二个User对象时,应该将group.setId()要设置成“经理”组的id.
追问:
我设置级联是all,比如说“经理”里面有个ID是1,我在插入第二个User的时候,将group.setId(1),插入数据,但是,数据插入成功了,"经理",这个组里ID为一的值变成NULL了
追答:
把xml配置或者注解方式的配置贴出来吧
追问:
group配置
<?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.bjsxt.hibernate.Group" table="t_group">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
</class>
</hibernate-mapping>
user配置
<?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.bjsxt.hibernate.User" table="t_user">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<many-to-one name="group" column="groupid" cascade="all"/>
<!--
<many-to-one name="group" column="groupid"/>
-->
</class>
</hibernate-mapping>
hibernate配置
<!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_many2one</property>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">123456</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.show_sql">true</property>
<mapping resource="com/bjsxt/hibernate/User.hbm.xml"/>
<mapping resource="com/bjsxt/hibernate/Group.hbm.xml"/>
</session-factory>
</hibernate-configuration>
运行的代码:
public void testSave3() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Group group = new Group();
group.setName("经理");
User user1 = new User();
user1.setName("小菜");
user1.setGroup(group);
User user2 = new User();
user2.setName("容祖儿");
user2.setGroup(group);
//不会抛出异常,因为采用了cascade属性,所以它会先保存Group
//采用cascade属性是解决TransientObjectException异常的一种手段
session.save(user1);
session.save(user2);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
追答:
上述方式由于没有设定Group的ID,它会生成两个组,这两个组ID分别使用自增长方式插入到数据库中。
假设你现在有Goup的id为1组,用如下代码试一试:
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Group group = session.get(Group.class,1);
User user1 = new User();
user1.setName("小菜");
user1.setGroup(group);
User user2 = new User();
user2.setName("容祖儿");
user2.setGroup(group);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}