Question

我正在尝试使用JPA＆amp; amp;来构建一个小项目。 EJB，但我已经陷入了很早的阶段......

这是问题所在。

我有三个实体 - 客户 - 项目 - 租赁

正如您可以从名称中获得，客户租赁（多对一）和物品租赁（多对一）。因此，Rental实体将Customer和Item实体的ID存储为外键。

我通过在persistence.xml中使用hibernate.hbm2ddl.auto属性实现了这个

    <persistence-unit name="JPADB">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <jta-data-source>java:/MySQLDS</jta-data-source>
        <exclude-unlisted-classes>false</exclude-unlisted-classes> 
        <properties>
            <property name="hibernate.archive.autodetection" value="class" />
            <property name="hibernate.format_sql" value="true" />
            <property name="showSql" value="true" />
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" />
            <property name="hibernate.hbm2ddl.auto" value="update" />
        </properties>
    </persistence-unit>
</persistence>

客户

@Entity
public class Customer implements Serializable{
    private static final long serialVersionUID = 1L;
    public Customer() {super();}

    @Id
    @Column(name = "customer_id")
    @GeneratedValue
    private int customerId;
    @Column(name = "customer_name")
    private String customerName;
    @OneToMany(targetEntity=Rental.class, mappedBy="customer", cascade=CascadeType.ALL, fetch=FetchType.EAGER)
    private List<Rental> rentals;

物品

@Entity
public class Item implements Serializable{
    private static final long serialVersionUID = 1L;
    public Item() {super();}

    @Id
    @Column(name = "item_id")
    @GeneratedValue
    private int itemId;
    @Column(name = "item_name")
    private String itemName;
    @OneToMany(targetEntity=Rental.class, mappedBy="item", cascade=CascadeType.ALL, fetch=FetchType.EAGER)
    private List<Rental> rentals;

租赁

@Entity
public class Rental implements Serializable{
    private static final long serialVersionUID = 1L;
    public Rental(){super();}

    @Id
    @Column(name = "rental_id")
    @GeneratedValue
    private int rentalId;
    private String rentalName;
    @ManyToOne(targetEntity = Customer.class)
    @JoinColumn(name="customer_id", nullable = false)
    private Customer customer;
    @ManyToOne(targetEntity = Item.class)
    @JoinColumn(name="item_id", nullable = false)
    private Item item;

我用下面的代码测试它

@Override
    public void saveCustomer(Customer customer) {
        if(entityManager.contains(customer))
            entityManager.merge(customer);
        else
            entityManager.persist(customer);
    }

只有当我摆脱Customer和Rent实体之间的关系时，代码才能正常工作，这实际上是通过阻止引用Customer实体中的私有List租赁的代码来实现一对多。如果我试试这个就会给我这个错误

log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
Exception in thread "main" java.lang.reflect.UndeclaredThrowableException
    at com.sun.proxy.$Proxy0.retrieveAllItems(Unknown Source)
    at com.hidvd.client.HiDVDApplicationClient.main(HiDVDApplicationClient.java:28)
Caused by: java.lang.ClassNotFoundException: org.hibernate.collection.internal.PersistentBag
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Unknown Source)
    at org.jboss.marshalling.AbstractClassResolver.loadClass(AbstractClassResolver.java:135)
    at org.jboss.marshalling.AbstractClassResolver.resolveClass(AbstractClassResolver.java:116)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadClassDescriptor(RiverUnmarshaller.java:892)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadNewObject(RiverUnmarshaller.java:1204)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:272)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:209)
    at org.jboss.marshalling.river.RiverUnmarshaller.readFields(RiverUnmarshaller.java:1677)
    at org.jboss.marshalling.river.RiverUnmarshaller.doInitSerializable(RiverUnmarshaller.java:1593)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadNewObject(RiverUnmarshaller.java:1235)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:272)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:209)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadCollectionObject(RiverUnmarshaller.java:180)
    at org.jboss.marshalling.river.RiverUnmarshaller.readCollectionData(RiverUnmarshaller.java:771)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:649)
    at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:209)
    at org.jboss.marshalling.AbstractObjectInput.readObject(AbstractObjectInput.java:37)
    at org.jboss.ejb.client.remoting.MethodInvocationResponseHandler$MethodInvocationResultProducer.getResult(MethodInvocationResponseHandler.java:107)
    at org.jboss.ejb.client.EJBClientInvocationContext.getResult(EJBClientInvocationContext.java:270)
    at org.jboss.ejb.client.TransactionInterceptor.handleInvocationResult(TransactionInterceptor.java:47)
    at org.jboss.ejb.client.EJBClientInvocationContext.getResult(EJBClientInvocationContext.java:272)
    at org.jboss.ejb.client.ReceiverInterceptor.handleInvocationResult(ReceiverInterceptor.java:132)
    at org.jboss.ejb.client.EJBClientInvocationContext.getResult(EJBClientInvocationContext.java:260)
    at org.jboss.ejb.client.EJBClientInvocationContext.awaitResponse(EJBClientInvocationContext.java:399)
    at org.jboss.ejb.client.EJBInvocationHandler.doInvoke(EJBInvocationHandler.java:140)
    at org.jboss.ejb.client.EJBInvocationHandler.doInvoke(EJBInvocationHandler.java:121)
    at org.jboss.ejb.client.EJBInvocationHandler.invoke(EJBInvocationHandler.java:104)
    ... 2 more

之前我曾使用hibernate会话练习过这个，但我需要使用JPA Annotation和JPA EntityManager来实现这一点。

我在项目中包含了hibernate库，但没有区别。

这是我对Enterprise Java的第一次尝试，我对自己的学习能力感到沮丧。希望你们能帮助我。

如果有人能给我一个实现DVD租赁商店数据库的EJB + JPA项目的示例代码，我将非常感激。我这样做是为了得到一份工作（我已经失去了机会......但我真的想完成这个以备将来的机会）。

帖子太长了。感谢您阅读本文。：）

**这是我的jar文件列表 enter image description here

Answer 1

你的类路径中至少缺少一个Hibernate jar：hibernate-core。至少你需要hibernate-entitymanager + hibernate-core +。

TBH这就是为什么项目通常采用某种形式的依赖管理，如Maven或Gradle或Ivy或......

（JPA）无法与hibernate.hbm2ddl.auto正确实现多对一关系

1 个答案: