Question

我正在尝试使用此测试项目首次使用hibernate实现设置JPA。遇到以下错误：

Exception in thread "main" javax.persistence.PersistenceException: [PersistenceUnit: ExamModulePu] Unable to build EntityManagerFactory
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:924)
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:899)
at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:59)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:63)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:47)
at service.tests.ExamServiceTest.main(ExamServiceTest.java:18)
Caused by: org.hibernate.AnnotationException: @OneToOne or @ManyToOne on entities.Question.examId references an unknown entity: long
at org.hibernate.cfg.ToOneFkSecondPass.doSecondPass(ToOneFkSecondPass.java:109)
at org.hibernate.cfg.Configuration.processEndOfQueue(Configuration.java:1536)
at org.hibernate.cfg.Configuration.processFkSecondPassInOrder(Configuration.java:1457)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1365)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1756)
at org.hibernate.ejb.EntityManagerFactoryImpl.<init>(EntityManagerFactoryImpl.java:96)
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:914)

这些是我的实体：

@Entity
public class Exam implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    private String name;
    private int numQuestions;
    private int minutesAllotted;
    private Date startDate;
    private Date endDate;
    @OneToMany(mappedBy = "examId", orphanRemoval = true)
    private List<Question> questionList;
        // Getters and setters here..
}

@Entity
public class Question implements Serializable{

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private long id;
    @ManyToOne
    private long examId;
    private int points;
    private int timeLimit;
    private String text;
    private String category;
    @Embedded
    private List<Answer> answerList;
}

@Embeddable 
public class Answer implements Serializable {

    private int optionNumber;
    private String text;
    private boolean correct;
}

这就是我的persistence.xml的样子：

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
    version="2.0">
    <persistence-unit name="ExamModulePu"
        transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <class>entities.Exam</class>
        <class>entities.Question</class>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/exammoduledb" />
            <property name="javax.persistence.jdbc.user" value="root" />
            <property name="javax.persistence.jdbc.password" value="root" />
            <property name="hibernate.hbm2ddl.auto" value="create" />
        </properties>
    </persistence-unit>
</persistence>

我没有创建任何表格，而是取决于hibernate.hb2mddl.auto这样做。但我相信我的错误甚至在发生之前就会出现，因为它无法生成持久性单元。我有什么想法我做错了吗？我确保只导入javax.persistence.*;

Answer 1

如果仔细观察堆栈跟踪，您会看到

Caused by: org.hibernate.AnnotationException: @OneToOne or @ManyToOne on entities.Question.examId references an unknown entity: long

所以这个领域

@ManyToOne
private long examId;

造成了这个问题。 @ManyToOne有一个参数targetEntity，其中说：

（可选）作为关联目标的实体类。默认为存储关联的字段或属性的类型。

由于您尚未提供该参数，因此默认为long，而不是托管Entity。

您可能想要使用

@ManyToOne(targetEntity = Exam.class)
private long examId;

否则它将不知道要映射到什么。或者甚至更好

@ManyToOne
private Exam exam;

Answer 2

只需将 Team 类添加到“hibernate-cfg.xml”文件中，因为Hibernate在没有添加的情况下无法识别。

Answer 3

仅供参考，如果您有一个休眠注释，有时会发生这种情况：

@org.hibernate.annotations.Entity

和JPA注释：

@javax.persistence.Entity

混淆

编辑：

显式导入javax注释。

Answer 4

我花了几个小时才找到实际问题

我忘记了 Parent 类上的 @Entity 注释以及用于显示在子类上的错误。

Answer 5

就我而言，Hibernate 无法识别实体，因为我没有使用 .addAnnotatedClass(XYZ.class) 在 sessionfactory 中添加该实体，因此无法找到该特定实体。

org.hibernate.AnnotationException：@OneToOne或@ManyToOne on entities.Ques＃tion.examId引用一个未知实体：long

5 个答案: