java - 延迟初始化异常 : could not initialize proxy - no Session

Question

我用 spring-data-jpa与 spring-boot(v2.0.0.RELEASE) ，我刚刚在MySQL上写了一个CRUD的demo，但是运行时出现异常，源码如下:

源代码

用户.java

@Entity
public class User implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    private Integer id;
    private String username;
    private String password;

    ...getter&setter
} 

用户存储库.java

public interface UserRepository extends JpaRepository<User, Integer> {

}

用户服务测试.java

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserServiceTest {

    @Autowired
    private UserRepository userRepository;

    @Test
    public void getUserById() throws Exception{
        userRepository.getOne(1);
    }

}

application.yml

spring:
  datasource:
    username: ***
    password: ***
    driver-class-name: com.mysql.jdbc.Driver
    url: ********
  thymeleaf:
    cache: false
  jpa:
    show-sql: true
    hibernate:
      ddl-auto: update

异常详情

org.hibernate.LazyInitializationException: could not initialize proxy - no Session

at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:155)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:268)
at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:73)
at cn.shuaijunlan.sdnsecuritysystem.domain.po.User_$$_jvstc90_0.getUsername(User_$$_jvstc90_0.java)
at cn.shuaijunlan.sdnsecuritysystem.service.UserServiceTest.getUserById(UserServiceTest.java:33)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)

I try to another method userRepository.findOne(1), it can run successfully.

Answer 1

您可以添加 @Transactional注释到您的测试方法以避免此异常。

方法getOne返回可以延迟加载属性的实体的“引用”(代理)。看到它code - 它使用 getReference EntityManager的方法.从它javadoc:

Get an instance, whose state may be lazily fetched.

在 Spring 中实现 EntityManager是 org.hibernate.internal.SessionImpl - 所以如果没有 Session Spring 就无法获得这个方法。

要进行 session ，您只需创建一个事务...