Question

我想使用Hibernate（在Java中）实现一对多关系。我有两个实体：

实验
ExperimentGroup

Experiment有很多ExperimentGroups。我尝试配置这种一对多关系，就像官方Hibernate文档推荐的那样：http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html/example-parentchild.html#example-parentchild-cascades

我的配置文件：

<class name="ExperimentImpl" table="Experiment">
    <id name="id" type="int" column="id">
        <generator class="increment" />
    </id>
    <!-- One to Many   -->
    <set name="experimentGroups" table="ExperimentGroup" 
                lazy="false" fetch="select" cascade="all" inverse="true">
            <key>
                <column name="Experiment_id" not-null="true" />
            </key>
            <one-to-many class="ExperimentGroupImpl" />
    </set>  
</class>
<class name="ExperimentGroupImpl" table="ExperimentGroup">
    <id name="id" type="int" column="id">
        <generator class="increment" />
    </id>
    <many-to-one name="experiment" class="ExperimentImpl" fetch="select">
            <column name="Experiment_id" not-null="true" />
    </many-to-one>
</class>

向ExperimentGroup添加新的Experiment可以正常工作，但删除实验（及其所有ExperimentGroup）会导致异常：

无法删除或更新父行：外键约束失败（testdb。ExperimentGroup，CONSTRAINT FK9C71D86238B5500C外国 KEY（Experiment_id）参考Experiment（id））

我的ExperimentDAO代码如下所示：

public void deleteExperiment(Experiment experiment) 
         throws DAOException
    {
        Session session = null;
        Transaction t = null;
        try{
            session = HibernateUtil.getSessionFactory().openSession();
            t = session.beginTransaction();
                session.delete(experiment);
            t.commit();
            session.flush();
            session.close();
        }catch (HibernateException e)
        {
            e.printStackTrace();
            if (t != null)
                t.rollback();

            if (session != null)
                session.close();

            throw new DAOException(e, "Could not delete Experiment");
        }
    }

修改用于创建实验和实验组的DAO代码：

public Experiment createExperiment(String name, String description, RegisteredUser owner)
{
    Transaction tx = null;
    Session session = null;
    try
    {
        session = HibernateUtil.getSessionFactory().openSession();

        tx= session.beginTransaction();
        ExperimentImpl e = new ExperimentImpl();

        e.setName(name);
        e.setDescription(description);
        e.setOwner(owner);

        owner.getOwnedExperiments().add(e);

        session.save(e);
        tx.commit();
        session.flush();
        session.close();

        return e;
    } catch (HibernateException ex )
    {
        if (tx != null)
            tx.rollback();

        if (session!=null)
            session.close();

        throw ex;
    }
}




public ExperimentGroup createAndAddExperimentGroup(Experiment experiment, String experimentGroupName, Date startDate, Date endDate) throws ArgumentException
    {

        Transaction t = null;
        Session session = null;

        try
        {
            session = HibernateUtil.getSessionFactory().openSession();
            t = session.beginTransaction();
                ExperimentGroupImpl g = new ExperimentGroupImpl();
                g.setEndDate(endDate);
                g.setStartDate(startDate);
                g.setName(experimentGroupName);
                g.setExperiment(experiment);

                experiment.getExperimentGroups().add(g);
                g.setExperiment(experiment);

                session.save(g);
                session.update(experiment);
            t.commit();
            session.flush();
            session.close();

            return g;

        }catch(HibernateException e)
        {
            if (t!=null)
                t.rollback();

            if (session!= null)
                session.close();

            throw e;
        }
    }

实验还有许多其他属性，例如我从配置文件中删除的名称，描述等，因为它们对一对多关系没有影响。

有什么建议吗？我错了什么？

Answer 1

我的印象是您正在尝试删除手动创建的分离实体。我会尝试使用您要删除的实验的主键，并在实际删除之前加载：

session = HibernateUtil.getSessionFactory().openSession();
t = session.beginTransaction();
ExperimentImpl persistentExperiment = session.load(ExperimentImpl.class, experiment.getId());
session.delete(persistentExperiment);
t.commit();

Hibernate：双向一对多外键约束失败

1 个答案: