Eclipselink：从实体生成表失败

我在从实体生成JPA表方面遇到了一些问题（在Eclipse4.3上使用Dali和eclipselink 2.5.0）。 我有一本实体书，它有几个属性，其中有一个

Category

属性。 类别也是一个实体，具有名称、描述和自动生成的id。关系为

图书M:1分类

以下是相关的代码片段

这本书

@Entity
public class Book implements Serializable {

    // bi-directional many-to-one association to Category
    @ManyToOne
    @JoinColumn(name = "CATEGORY_ID", nullable = false)
    private Category category;

    // other attributes, constructors and methods...
}

类别

@Entity
public class Category implements Serializable {


    // bi-directional one-to-many association to Book
    @OneToMany(mappedBy = "category", cascade = { CascadeType.PERSIST }, fetch = FetchType.LAZY)
    private Set<Book> books;

    // other attributes, constructors and methods...
}

类别被注释为

@Entity

，它也包含在persistence.xml文件中。 我的问题是，是什么导致了这个问题？我忘了什么？因为就我所知，类别是一个实体

@StaticMetamodel(Book.class)
public class Book_ { 

    public static volatile SingularAttribute<Book, Category> category;
    // ....
}

@StaticMetamodel(Category.class)
public class Category_ {

    public static volatile SetAttribute<Category, Book> books;
    // ....
}

Exception in thread "main" Local Exception Stack: 
Exception [EclipseLink-30005] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): 
    org.eclipse.persistence.exceptions.PersistenceUnitLoadingException
Exception Description: An exception was thrown while searching for persistence archives with ClassLoader: 
    org.eclipse.persistence.dynamic.DynamicClassLoader@154e92c
Internal Exception: javax.persistence.PersistenceException: Exception [EclipseLink-28018]
    (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.EntityManagerSetupException
    Exception Description: Predeployment of PersistenceUnit [bookstore] failed.
Internal Exception: Exception [EclipseLink-7250] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): 
    org.eclipse.persistence.exceptions.ValidationException
Exception Description: [class name.kipchumba.obby.bookstore.entities.Book] 
uses a non-entity [class name.kipchumba.obby.bookstore.entities.Category] as target entity in the relationship attribute [field category].
    at org.eclipse.persistence.exceptions.PersistenceUnitLoadingException.exceptionSearchingForPersistenceResources(PersistenceUnitLoadingException.java:127)
    at org.eclipse.persistence.jpa.PersistenceProvider.createEntityManagerFactoryImpl(PersistenceProvider.java:107)
    at org.eclipse.persistence.jpa.PersistenceProvider.createEntityManagerFactory(PersistenceProvider.java:177)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:79)
    at org.eclipse.jpt.jpa.eclipselink.core.ddlgen.Main.buildEntityManagerFactory(Main.java:94)
    at org.eclipse.jpt.jpa.eclipselink.core.ddlgen.Main.execute(Main.java:80)
    at org.eclipse.jpt.jpa.eclipselink.core.ddlgen.Main.main(Main.java:68)