我们在指定了数据库表的关联映射后,在删除其中一方的的时候,提示了以下异常:deleted object would be re-saved by cascade (remove deleted object from associations): [entity.Associationinformation#7]
(注:entity.Associationinformation是实体类,7为设定的外键的值)
下面是我的多对一关联情况:
1、实体类:
entity.Associationinformation和entity.Associationactivitylist,前者为one,后者为many。
Associationinformation.java:
public class Associationinformation implements java.io.Serializable { private Integer assoId; private String assoName; private String assoPosition; private Integer assoPersonNum; private String assoBuildDate; private String assoIntroduce; private String assoServiceObject; //一对一的社团负责人 private Associationrespeople assoResID; //一对多的社团活动 private Set<Associationactivitylist> assoActivity; //省略get/set方法 }
Associationactivitylist.java:
public class Associationactivitylist implements java.io.Serializable { private Integer activityId; private String activityName; private String activityPosition; private Integer activityPersonNum; private String activityTime; private String activityContent; private Associationinformation association; //省略get/set方法 }
2、映射文件:*.hbm.xml
Associationinformation.hbm.xml:
<hibernate-mapping> <class name="entity.Associationinformation" table="associationinformation" catalog="stu_association"> <id name="assoId" type="java.lang.Integer"> <column name="AssoID" /> <generator class="increment" /> </id> <property name="assoName" type="java.lang.String"> <column name="AssoName" length="20" /> </property> <property name="assoPosition" type="java.lang.String"> <column name="AssoPosition" length="20" /> </property> <property name="assoPersonNum" type="java.lang.Integer"> <column name="AssoPersonNum" /> </property> <property name="assoBuildDate" type="java.lang.String"> <column name="AssoBuildDate" length="10" /> </property> <!-- <property name="assoResName" type="java.lang.String"> <column name="AssoResName" length="20" /> </property>--> <property name="assoIntroduce" type="java.lang.String"> <column name="AssoIntroduce" length="150" /> </property> <property name="assoServiceObject" type="java.lang.String"> <column name="AssoServiceObject" length="20" /> </property> <!-- 一对多的社团与社团活动 --> <set name="assoActivity" table="associationactivitylist"> <key column="assoID"></key> <one-to-many class="entity.Associationactivitylist"/> </set> <!-- 一对一的社团负责人 --> <many-to-one name="assoResID" class="entity.Associationrespeople" column="assoResID" lazy="false" cascade="all" unique="true" ></many-to-one> </class> </hibernate-mapping>
Associationactivitylist.hbm.xml:
<hibernate-mapping> <class name="entity.Associationactivitylist" table="associationactivitylist" catalog="stu_association"> <id name="activityId" type="java.lang.Integer"> <column name="ActivityID" /> <generator class="increment" /> </id> <property name="activityName" type="java.lang.String"> <column name="ActivityName" length="20" not-null="true" /> </property> <property name="activityPosition" type="java.lang.String"> <column name="ActivityPosition" length="20" not-null="true" /> </property> <property name="activityPersonNum" type="java.lang.Integer"> <column name="ActivityPersonNum" /> </property> <property name="activityTime" type="java.lang.String"> <column name="ActivityTime" length="10" not-null="true" /> </property> <property name="activityContent" type="java.lang.String"> <column name="ActivityContent" length="150" /> </property> <!-- 配置多对一关联关系 --> <many-to-one name="association" class="entity.Associationinformation" column="assoID" cascade="all"> </many-to-one> </class> </hibernate-mapping>
记得在Hibernate.cfg.xml中声明映射文件的路径:
<mapping resource="entity/Associationinformation.hbm.xml" /> <mapping resource="entity/Associationactivitylist.hbm.xml" />
到这里就完成了一对多的关联配置,然后在Action中写Delete()方法:
public String deleteActivity(){ ... Transaction tx = HibernateSessionFactory.getSession().beginTransaction(); assoActivityDao.delete(associationactivitylist); tx.commit(); HibernateSessionFactory.closeSession(); ... }
请注意,这样写的话,就会报出以上异常,如果没有关联关系,这样写是可以的。结合了网上的方法,解决方法如下:
1、删除Set方的cascade:(缺点:子对象和父对象不能进行级联更新,没意义)
2、解决关联关系后,再删除(个人推荐):
将Action中的方法改为:
public String deleteActivity(){ ... Associationactivitylist associationactivitylist = assoActivityDao.findById(AssoID); Associationinformation Association = associationactivitylist.getAssociation(); Association.getAssoActivity().remove(associationactivitylist); associationactivitylist.setAssociation(null); Transaction tx = HibernateSessionFactory.getSession().beginTransaction(); assoActivityDao.delete(associationactivitylist); tx.commit(); HibernateSessionFactory.closeSession(); ... }
分别获取到社团和社团活动对象后,利用remove方法解除关联管理,再将one方的值设为null。