使用OpenJPA从数据库中检索主键（ID）（？） [英] Primary Key (ID) not retrieved (?) from database using OpenJPA

问题描述

这是一个写入和读取mysql数据库的简单程序。当我输入测试数据时，所有这些都在mySQL客户端中可见。然而，当我使用OpenJPA检索相同的数据时，所有ID都显示为0，但名称是正确的。在交易过程中ID可能会丢失的原因是什么？

This is a simple program to write to and read from a mysql database. When I enter the test data, all of it is visible in the mySQL client. Yet, when I use OpenJPA to retrieve the same data, all the ids appear "0", but the names are correct. What might be the cause for IDs to get lost during the transaction?

POJO等级

import java.io.Serializable;

import javax.persistence.*;

@Entity (name="People")
public class People implements Serializable{

/**
 * 
 */
private static final long serialVersionUID = 801578124126646759L;

@Id
private int id;

@Column(length=32)
private String name;

public People(int id,String name)
{
    setId(id);
    setName(name);
}

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}   

}

从数据库中读取的类

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.Query;


 public class PeopleGetter {

EntityManager entityManager;

public PeopleGetter(EntityManager entityManager)
{
    this.entityManager=entityManager;
}

@SuppressWarnings("unchecked")
public List<People> getAllPeople()
{
    Query query=entityManager.createQuery("SELECT x FROM People x");
    return query.getResultList();
}

}

打印数据的类

import java.io.PrintStream;
import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.Query;

public class PeoplePrinter {

private PeopleGetter peopleGetter;

private PrintStream out = System.out;

public PeoplePrinter(PeopleGetter peopleGetter)
{
    this.peopleGetter=peopleGetter;
}

public void setPrintStream (PrintStream stream){
    out = stream;
}

public void getAllPeopleAndPrint() 
{
    List<People>peopleList=peopleGetter.getAllPeople();
    for(People person: peopleList) {
        out.println(person.getId()+"=>"+person.getName());
    }
}
}

Main Tester类

Main Tester class

import javax.persistence.*;


public class MainClass {

public static void generateNames()
{
    EntityManager entityManager = getEntityManager();
    EntityTransaction userTransaction = entityManager.getTransaction();
    userTransaction.begin();
    entityManager.persist(new People(1,"Ali"));
    userTransaction.commit();
    userTransaction.begin();
    entityManager.persist(new People(2,"Veli"));
    userTransaction.commit();
    userTransaction.begin();
    entityManager.persist(new People(3,"Ahmet"));
    userTransaction.commit();
    userTransaction.begin();
    entityManager.persist(new People(4,"Mehmet"));
    userTransaction.commit();       
    entityManager.close();
}

public static EntityManager getEntityManager()
{
     EntityManagerFactory entityManagerFactory =      Persistence.createEntityManagerFactory("openjpa");
     EntityManager entityManager = entityManagerFactory.createEntityManager();
     return entityManager;
}

public static void resetTable()
{
    EntityManager em = getEntityManager();
    Query query = em.createQuery("DELETE FROM People x");
    EntityTransaction userTransaction = em.getTransaction();
    userTransaction.begin();
    query.executeUpdate();
    userTransaction.commit();
    em.close();
}

public static void main(String[] args)
{
        resetTable();
        generateNames();
        EntityManager em = getEntityManager();
        PeoplePrinter peoplePrinter=new PeoplePrinter(new PeopleGetter(em));
        peoplePrinter.getAllPeopleAndPrint();   
        em.close();
}
 }

提前致谢。

推荐答案

我假设你正在使用Eclipse增强器，它有几个已知错误。我建议你去 uild time或者javaagent 增强器。

I assume you're using the Eclipse enhancer, which has a couple of known bugs. I'd advise getting build time or the javaagent enhancer going.

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