弹簧启动 2.Jackson json 序列化或 Spring Data JPA FetchType.Lazy.

我的情况非常奇怪，坦率地说，我不完全确定这是杰克逊序列化问题还是与Spring Data JPA有关，它如何获取懒惰对象

春季 2.0.2

弹簧-引导-启动器-数据-JPA
弹簧启动启动网
弹簧引导开发工具
MySQL-connector-java

当您搜索大多数人对杰克逊的问题时，序列化是会话外的懒惰获取导致以下异常。但是，我根本没有得到这个例外....

org.hibernate.LazyInitializationException：无法初始化代理 - 无会话

问题

它实际上在我的控制器中获取数据并返回 json 对象(下面的休眠查询(。急切地获取是一个问题，因为它会获取未使用的不必要的大数据。

结构(省略吸气剂和设置器以使螺纹更短(

User
| <---[ OneToMany ]        
Employee { hierarchies entity }
|
+-----+-----+
|           |
PartTime   FullTime

用户

@Entity
public class User {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@OneToMany(mappedBy="user")
@JsonIgnoreProperties("user")
private List<Employee> employee = new ArrayList<>();

恩波利

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class Employee {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@ManyToOne
@JsonIgnoreProperties("employee")
private User user;

全职/兼职(兼职时现场工资更改为小时工资(

@Entity
public class FullTime extends Employee  {
private BigDecimal salary;

UserRepository 扩展了 CrudRepository

用户服务

public User getUserById(Long id) {
Optional<User> optionalUser = userRepo.findById(id);
User user = optionalUser.get();
logger.info("n User -> {}", user);
return user;
}

控制器

@RestController
@RequestMapping(value="/api/user")
public class UserController {
@GetMapping(value="/{userId}" )
public User getUser(@PathVariable("userId") Long id) {
return userService.getUserById(id);
}   
}

在我的应用程序上扩展了命令行运行程序，它允许我在应用程序启动时运行命令

@Override
public void run(String... args) throws Exception {
logger.info("users 1 -> {}" , userService.getUserById(1L));
}

Hibernate: 
select
user0_.id as id1_3_0_,
user0_.name as name2_3_0_ 
from
user user0_ 
where
user0_.id=?
INFO 14434 --- [  restartedMain] ication$$EnhancerBySpringCGLIB$$6cf0457c :     
users 1 -> 
User [id=1, name=Jack]

但是当我通过我的控制器时http://localhost:8080/api/user/1我收到 2 个单独的休眠调用，这两个调用似乎都在我的服务层内。请记住，我的服务层我没有事务性，所以它真的很奇怪......

Hibernate:  << 1st
select
user0_.id as id1_3_0_,
user0_.name as name2_3_0_ 
from
user user0_ 
where
user0_.id=?
com.example.app.service.UserService      : << -- In service 
User -> 
User [id=1, name=Jack]
Hibernate: 
select
employee0_.user_id as user_id2_0_0_,
employee0_.id as id1_0_0_,
employee0_.id as id1_0_1_,
employee0_.user_id as user_id2_0_1_,
employee0_1_.salary as salary1_1_1_,
employee0_2_.hourly_wage as hourly_w1_2_1_,
case 
when employee0_1_.id is not null then 1 
when employee0_2_.id is not null then 2 
when employee0_.id is not null then 0 
end as clazz_1_ 
from
employee employee0_ 
left outer join
full_time employee0_1_ 
on employee0_.id=employee0_1_.id 
left outer join
part_time employee0_2_ 
on employee0_.id=employee0_2_.id 
where
employee0_.user_id=?

现在，如果这是我访问过的杰克逊序列化问题避免对未获取的惰性对象进行杰克逊序列化，将 Jackson 配置为在 Spring 启动中省略延迟加载属性，以及更多，但所有这些都是通过扩展 WebMvcConfigurerAdapter 完成的，我相信在 spring5 中已被弃用？

如果它与Spring Data JPA有关...那么请阐明一些信息，因为我一直认为您需要@Transaction惰性 Fetch 的注释才能将关系与休眠会话相关联......

对不起，线程太长...

我认为您已启用属性spring.jpa.open-in-view(默认值为true(。检查您是否在日志中看到以下消息：

spring.jpa.open-in-view is enabled by default. Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable this warning

如果禁用它，您应该会看到所需的异常。

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