java - JPA:orphanRemoval=true 删除时有时会抛出 NullPointerException

Question

我正在使用 JPA 2.1、EclipseLink 2.5.0、SQLite3 数据库和 Swing 制作一个应用程序。

我有两个实体，EntityClient和EntityPhone ，其中第一个有 OneToMany与第二个的关系。两个实体都有自己的主键，它们的关系由 JoinTable 表示。 。为了访问和保留所有数据，我使用通用 DAO .

我试图级联删除，所以如果删除客户端，他的手机也会被删除。我已经通过添加 orphanRemoval=true 实现了这一点和cascade={CascadeType.ALL}到OneToMany注释和 CascadeOnDelete注解。

问题是，由于 orphanRemoval=true ，如果我插入一个新客户端，然后尝试删除它，我将得到 NullPointerException 。但如果我关闭应用程序并再次启动它，它会让我毫无问题地删除客户端。

这些是实体:

@Entity
@Table(name="clientes")
public class EntityClient {

    @Id
    @Column(name="id_cliente")
    private Integer idClient;

    @Column(name="nombre")
    private String name;

    @Column(name="apellidos")
    private String surname;

    @OneToMany(mappedBy="client",
               targetEntity=EntityPhone.class,
               fetch=FetchType.EAGER,
               orphanRemoval=true,
               cascade={CascadeType.ALL})
    @CascadeOnDelete
    private ArrayList<EntityPhone> phones;

    //The rest of the fields and the getters and setters...
}

@Entity
@Table(name="telefonos")
public class EntityPhone {

    @Id
    @Column(name="id_telefono")
    private Integer idPhone;

    @Column(name="telefono")
    private String phone;

    @Column(name="descripcion")
    private String description;

    @ManyToOne(fetch=FetchType.EAGER)
    @JoinTable(name="clientes_telefonos",
               joinColumns=@JoinColumn(name="id_telefono",
                                       referencedColumnName="id_telefono"),
               inverseJoinColumns=@JoinColumn(name="id_cliente",
                                              referencedColumnName="id_cliente"))
    private EntityClient client;

    //Getters and setters...
}

这是通用的DAO显然有一个删除方法:

public abstract class DAO<Entity, ID extends Serializable> {

    private Class<Entity> entityClass;

    private final static EntityManagerFactory emf = Persistence.createEntityManagerFactory("Database_Name");
    private final static EntityManager em = emf.createEntityManager();


    public void delete(ID id) throws PersistenceException {

            em.getTransaction().begin();

            Entity row = em.find(entityClass, id);

            em.remove(row);

            em.getTransaction().commit();
    }

    //...
}

这是我遇到的异常:

javax.persistence.RollbackException: java.lang.NullPointerException
    at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commit(EntityTransactionImpl.java:157)
    at model.dao.DAO.delete(DAO.java:127)
    at controller.delete.ControllerDeleteClient.actionPerformed(ControllerDeleteClient.java:39)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)
Caused by: java.lang.NullPointerException
    at org.eclipse.persistence.internal.queries.CollectionContainerPolicy.iteratorFor(CollectionContainerPolicy.java:150)
    at org.eclipse.persistence.mappings.CollectionMapping.recordPrivateOwnedRemovals(CollectionMapping.java:1724)
    at org.eclipse.persistence.internal.descriptors.ObjectBuilder.recordPrivateOwnedRemovals(ObjectBuilder.java:3445)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.calculateChanges(UnitOfWorkImpl.java:687)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.commitToDatabaseWithChangeSet(UnitOfWorkImpl.java:1514)
    at org.eclipse.persistence.internal.sessions.RepeatableWriteUnitOfWork.commitRootUnitOfWork(RepeatableWriteUnitOfWork.java:277)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.commitAndResume(UnitOfWorkImpl.java:1167)
    at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commit(EntityTransactionImpl.java:132)
    ... 38 more

Answer 1

您正在使用静态来保存您的EntityManager，这是一个坏主意 - 它不是线程安全的。您需要为每个上下文获取一个新的:

public void delete(ID id) throws PersistenceException {
    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();
    Entity row = em.find(entityClass, id);
    em.remove(row);
    em.getTransaction().commit();
}

这也可能有助于解决您当前的问题，该问题似乎是由于陈旧的缓存造成的。一些如何使用空电话集合管理您要删除的 EntityClient 实例。您可以提交一个错误，让 EclipseLink 处理 null 集合，但它实际上不应该为 null。由于此 EntityManager 是长期存在的(在类上是静态的)，因此您必须跟踪如何管理和创建此实体，并且该集合与引用它的 EntityPhone.client 关系保持同步。重新启动应用程序会清除缓存，因此查找操作将构建 EntityClient 的新实例，并正确填充集合，从而避免 NPE。您可以通过调用 em.refresh(entityClass) 获得相同的效果，但跟踪集合如何为 null 可能会给您带来更好的性能。