在数据库中搜索时，EntityManager为null和NullPointerException [英] EntityManager null and NullPointerException while searching in DB

问题描述

我真的是Java ee的菜鸟

i am really noob in java ee

我要查询以确认电子邮件是否唯一

i want to make a query to verify if email is unique

在网上搜索后，我很生气，得出的结论是我的EntityManeger为空

after i search on web i mad i came to conclusion that me EntityManeger is null

这是我的实体客户，是一个查询 Customer.findByEmail ，这是我的关注点

this is my entity Customer and is an query Customer.findByEmail that is my point of focus

@Entity
@Table(name = "customer")
@NamedQueries({
@NamedQuery(name = "Customer.findAll", query = "SELECT c FROM Customer c"),
@NamedQuery(name = "Customer.findById", query = "SELECT c FROM Customer c WHERE c.id = :id"),
@NamedQuery(name = "Customer.findByName", query = "SELECT c FROM Customer c WHERE c.name = :name"),
@NamedQuery(name = "Customer.findByEmail", query = "SELECT c FROM Customer c WHERE c.email = :email"),
(...)

我有一个名为CutomerFacade的会话

i have a session named CutomerFacade

@Stateless
public class CustomerFacade extends AbstractFacade<Customer> {
@PersistenceContext(unitName = "AffableBeanPU")
public EntityManager em;

public List<Customer> GetPorEmail(String match){
   return  em.createNamedQuery("Customer.findByEmail").setParameter("email", match).getResultList();
}

如何避免实体管理器中的为空

Whats the solution to avoid null in entity manager

推荐答案

确保您正在Java EE服务器上运行并通过容器访问SessionBean.

Ensure you are running in a Java EE server and accessing the SessionBean through the container.

您在哪台服务器上运行?您如何访问SessionBean?

What server are you running in? How do you access the SessionBean?

这篇关于在数据库中搜索时，EntityManager为null和NullPointerException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！