解决Hibernate删除异常：deleted object would be re-saved by cascade

Posted 2020-06-29

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。

本文出自 “w1sw” 博客，请务必保留此出处http://cfdeng.blog.51cto.com/9873532/1755553