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