JPA @Version字段不会增加

Question

我是JPA和Hibernate的新手,我遇到了乐观锁定的问题.我有一个有@Version注释字段的课程.当我更新此类所代表的实体时,版本计数器不会增加.这是我的代码:班级:

@Entity
@Table (name = "Studenten")
public class Student implements Serializable{

private static final long serialVersionUID = 705252921575133272L;

@Version
private int version;
private int matrnr;
private String name;
private int semester;


public Student (){

}
public Student (int matrnr, String name){
    this.matrnr = matrnr;
    this.name = name;
}

public Student (int matrnr, String name, int semester){
    this(matrnr, name);
    this.semester = semester;
}

这是主要方法:

public static void main(String[] args) {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("VEDA_Vortrag");
    EntityManager em = emf.createEntityManager();

    EntityTransaction tx = em.getTransaction();

    try{
        tx.begin();
        Student s = em.find(Student.class, 195948);
        s.setSemester(1);
        em.persist(s);
        tx.commit();
    }catch(Exception e){
        if(tx != null && tx.isActive()){
            tx.rollback();
            System.out.println("Error in Transaction. Rollback!");
        }
    }
    finally{
        em.close();
        emf.close();
    }
}

以下是控制台所说的内容:

Hibernate: 
select
    student0_.matrnr as matrnr0_0_,
    student0_.name as name0_0_,
    student0_.semester as semester0_0_,
    student0_.version as version0_0_ 
from
    Studenten student0_ 
where
    student0_.matrnr=?
Hibernate: 
    update
        Studenten 
    set
        name=?,
        semester=?,
        version=? 
    where
        matrnr=?

有人能告诉我什么是错的吗？

编辑: 好的,我尝试了一些东西.我已将锁定设置为LockModeType.OPTIMISTIC_FORCE_INCREMENT并获得此错误消息:

ERROR: HHH000099: an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session): org.hibernate.AssertionFailure: cannot force version increment on non-versioned entity
Jun 20, 2014 9:00:52 AM org.hibernate.AssertionFailure <init>

所以很明显我有一个非版本化的实体.但为什么？我班上有@Version Annotation.

编辑: 我开始认为问题出在persistence.xml中.这里是:

<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="VEDA_Vortrag">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <properties>
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/uni"/>
        <property name="javax.persistence.jdbc.user" value="*******"/>
        <property name="javax.persistence.jdbc.password" value="******"/>
        <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
        <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
        <property name="hibernate.show_sql" value="true"/>
        <property name="hibernate.format_sql" value="true"/>
    </properties>
</persistence-unit>

有什么不对的吗？

Answer 1

这可能不完全是主题（因为我使用的是 SpringData 存储库）但是当我在寻找问题的答案时，我最终来到了这里，所以这可能对下一个人有所帮助。

以下和我的版本字段没有被返回更新。

savedJpa = repository.save(updateJpa);

最后我的解决方案是

savedJpa = repository.saveAndFlush(updateJpa);

Answer 2

正如我在本文中解释的那样,该entityManager.persist()方法仅用于之前从未持久化的新实体.

因为您正在获取实体,所以无论如何都不需要调用persist或merge.在脏检查将做代表您的更新.

提交将始终触发刷新,因此您应该看到更新.

确保使用javax.persistence.Version注释而不是其他包(弹簧数据或类似的东西).