使用OpenJPA从数据库中检索主键（ID）（？）
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？
POJOclass
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 getAllPeople() { Query query=entityManager.createQuery("SELECT x FROM People x"); return query.getResultList(); } }
用于打印数据的类
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() { ListpeopleList=peopleGetter.getAllPeople(); for(People person: peopleList) { out.println(person.getId()+"=>"+person.getName()); } } }
主测试类
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。
我假设您正在使用Eclipse增强器，它有几个已知的错误 。 我建议你花点时间或javaagent增强器。