所有JPA查询都找不到任何结果（即使MySQL数据库中存在数据）

Question

我正在尝试设置爪哇。在我的项目中坚持不懈，我已经开始使用基本方法：实体管理器生成器 package olsa.amex.dao; import javax.persistence.*;  public class EntityManagerGenerator {private EntityManager currentSession;private EntityTransaction currentTransaction;public EntityManager openCurrentSession() {    if ((currentSession == null)||(currentSession != null && !currentSession.isOpen()))        currentSession = getSessionFactory().createEntityManager();    return currentSession;}public EntityManager openCurrentSessionwithTransaction() {    if ((currentSession == null)||(currentSession != null && !currentSession.isOpen()))        currentSession = getSessionFactory().createEntityManager();    currentTransaction = currentSession.getTransaction();    currentTransaction.begin();    return currentSession;}public void closeCurrentSession() {    if (currentSession != null && currentSession.isOpen())        currentSession.close();}public void closeCurrentSessionwithTransaction() {    if (currentSession != null && currentSession.isOpen()) {        currentTransaction.commit();        currentSession.close();    }}private static EntityManagerFactory getSessionFactory() {    EntityManagerFactory entityManager = Persistence.createEntityManagerFactory("JPAAmex");    return entityManager;}public EntityManager getCurrentSession() {    return currentSession;}public void setCurrentSession(EntityManager currentSession) {    this.currentSession = currentSession;}public EntityTransaction getCurrentTransaction() {    return currentTransaction;}public void setCurrentTransaction(EntityTransaction currentTransaction) {    this.currentTransaction = currentTransaction;}}

Answer 1

我发现了问题，显然这都是由错误的jdbc连接字符串引起的。为了生成实体，我使用了以下字符串：

jdbc:mysql://rmarjboss-001c.customer.olsa:3306/amex_digital_sbs_dev?useUnicode=yes&characterEncoding=UTF-8

我在坚持中使用的.xml是这样的：

jdbc:mysql://rmarjboss-001c.customer.olsa:3306/amex_digital_sbs_dev

为了使一切正常工作，我必须在持久性中设置正确的字符串.xml：

jdbc:mysql://rmarjboss-001c.customer.olsa:3306/amex_digital_sbs_dev?useUnicode=yes&characterEncoding=UTF-8