java - JPA query.getResultList() 返回错误的对象？

Question

我正在执行以下查询以测试 JPA 是否正在从数据库中检索预期结果。

我不明白为什么row instanceof Ativo返回错误。row.getClass()返回br.meuspila.entity.Ativo，打印的对象是br.meuspila.entity.Ativo[ id=1 ]。该类的导入是好的，并且同一个包内没有其他名为 Ativo 的类。

// OUTPUT:
INFO:   br.meuspila.entity.Ativo[ id=1 ]  // row
INFO:   false  // row instanceof Ativo?
INFO:   class br.meuspila.entity.Ativo  // row.getClass()

---

MyMB 类：

package br.meuspila.mb;

import br.meuspila.database.JpaUtil;
import br.meuspila.entity.Ativo;
import java.util.List;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.persistence.EntityManager;
import javax.persistence.EntityTransaction;
import javax.persistence.Query;

@ManagedBean
@SessionScoped
public class MyMB {

    public String teste = "testando, 123";

    /**
     * Creates a new instance of ManagedBean
     */
    public MyMB() {
    }

    public String getTeste() {
        return teste;
    }

    public void setTeste(String teste) {
        this.teste = teste;
    }

    public void actionTeste() {
        EntityManager em = JpaUtil.getInstance().createEntityManager();

        try {
            EntityTransaction t = em.getTransaction();
            t.begin();

            Query query = em.createQuery("select x from Ativo x");
            List result = query.getResultList();

            for (Object row : result) {
                System.out.println(row);
                System.out.println(row instanceof Ativo);
                System.out.println(row.getClass());
            }

            t.commit();

        } finally {
            em.close();
        }        
    }

}

---

JpaUtil 类：

package br.meuspila.database;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public final class JpaUtil {

    private JpaUtil() {
    }

    public static JpaUtil getInstance() {
        return JpaUtilHolder.INSTANCE;
    }

    private static class JpaUtilHolder {
        private static final JpaUtil INSTANCE = new JpaUtil();
        private static final EntityManagerFactory EMF = Persistence.createEntityManagerFactory("MeusPila3_WebPU");
    }

    public EntityManager createEntityManager() {
        return JpaUtilHolder.EMF.createEntityManager();
    }
}

---

持久性.xml：

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
  <persistence-unit name="MeusPila3_WebPU" transaction-type="JTA">
    <jta-data-source>jdbc/meuspiladb</jta-data-source>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <properties>
    </properties>
  </persistence-unit>
</persistence>

---

我的项目配置（Web 项目）：

JPA 2.1 - EclipseLink-2.5.0.v20130507-rNA
GlassFish Server 4

NetBeans IDE 7.3.1 (Build 201306052037)
Java: 1.7.0_25; Java HotSpot(TM) 64-Bit Server VM 23.25-b01
Runtime: Java(TM) SE Runtime Environment 1.7.0_25-b17
System: Windows 7 version 6.1 running on amd64; Cp1252; pt_BR (nb)

注意：JpaUtil类在br.meuspila.database包内。

Answer 1

随机装载机出现！如果没有看到整个应用程序，我会情不自禁——但在这里你可以快速解决：Ativo从你WEB-INF/lib的 .容器文档）。这样，由于委托，bean 类将始终从同一个加载器加载。

再次确保没有 bean 类定义存在WEB-INF（既不在 JAR 中，也不在普通的 .class 文件中）。如果您使用支持以下的构建工具，请尝试将 bean 放在单独的项目（子项目/模块/子模块）中，使其他项目依赖它，并将依赖范围设置为提供（或等效，即类是编译和测试需要，但不得包含在输出工件、war、jar 或 ear 中）

Answer 2

As suggested by @Rafaelle, I think the problem was my singleton class: JpaUtil. Fixed the code by deleting that class.

Maybe if I changed that class the problem would be solved. I was observing it and noticed that I did something (possibly) wrong: in the singleton I tried to create 2 instances inside the internal class (JpaUtilHolder)... Maybe I should remove EMF from that internal class and put it as a not static attribute of the JpaUtil class.

Replaced in MyMB:

EntityManager em = JpaUtil.getInstance().createEntityManager();

by

EntityManagerFactory emf = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT);
EntityManager em = emf.createEntityManager();

Answer 3

就我而言，实体的复合 PK 与表的 PK 不同。修复映射，解决问题。