org.hibernate.AnnotationException：entities.Ques#tion.examId 上的 @OneToOne 或 @ManyToOne 引用了一个未知实体：long

Question

I'm trying to setup JPA with a hibernate implementation for the first time with this test project. Ran into the following error:

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)

These are my entities:

@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;
}

This is what my persistence.xml looks like:

<?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>

I haven't created any of the tables, but instead am depending on the hibernate.hb2mddl.auto to do so. But I believe my error springs up even before that happens as it can't generate the persistence unit. Any ideas what I'm doing wrong? I'm making sure I import only javax.persistence.*;

Answer 1

If you look closely at your stacktrace, you will see

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

So this field

@ManyToOne
private long examId;

is causing the problem. @ManyToOne has a paramater targetEntity which says:

(Optional) The entity class that is the target of the association. Defaults to the type of the field or property that stores the association.

Since you haven't provided that parameter, it defaults to long , which is not a managed Entity .

You'll probably want to use

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

otherwise it won't know what to map to. Or even better

@ManyToOne
private Exam exam;

Answer 2

只需将类Team添加到“hibernate-cfg.xml”文件中，因为 Hibernate 不添加就无法识别。

Answer 3

FYI, this sometimes happens if you have a hibernate annotation:

@org.hibernate.annotations.Entity

and a JPA annotation:

@javax.persistence.Entity 

mixed up

Edit:

Explicitly import the javax annotation.

Answer 4

It took me hours to find the actual issue

I had forgotten the @Entity annotation on the Parent class and the error use to show on the child class.

Answer 5

在我的情况下，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。