Spring Boot JPA-延迟加载不适用于一对一映射 [英] Spring boot JPA - Lazy loading is not working for One to One mapping
问题描述
请注意，我已经看过类似的问题，并且已经解释了为什么它们没有为我工作
我有一个简单的Spring boot JPA-Hibernate应用程序，其中User和Address之间是一对一的映射. (请注意，我没有一对多映射的问题)
I have a simple Spring boot JPA-Hibernate application with one to one mapping between User and Address. (Please note that I do not have this issue with one to many mapping)
用户实体
@Entity
@Table(name = "users")
public class User implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private Integer id;
@Column
private String name;
@OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "user")
private Address address;
@OneToMany(fetch = FetchType.LAZY, mappedBy = "user")
private Set<Note> notes;
}
地址实体
@Entity
@Table(name = "addresses")
public class Address implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private Integer id;
@Column
private String street;
@Column
private String city;
@JsonIgnore
@OneToOne
@JoinColumn(name = "user_id")
private User user;
}
注释实体
@Entity
@Table(name = "notes")
public class Note implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private Integer id;
@Column
private String date;
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "user_id", nullable = false)
private User user;
}
我的问题是，每当我调用映射为要获取所有用户的控制器时，我都会得到该地址以及所有相关的注释.但是我希望FetchType.LAZY能够解决这个问题.
My problem is that whenever I call the controller mapped to get all users I was getting the address and all the associated notes with it as well. But I would expect FetchType.LAZY to take care of that.
我在StackOverflow上阅读了很多问题，提到杰克逊可能是罪魁祸首:
I read a lot of questions on StackOverflow mentioning that Jackson might be the culprit here:
我还阅读到spring.jpa.open-in-view defualt值可能是罪魁祸首:
I also read that spring.jpa.open-in-view defualt value might be the culprit:
所以我尝试了以下选项:
So i tried the following options:
我通过向application.properties添加spring.jpa.open-in-view=false来禁用默认打开的视图属性，该属性开始为我提供
I disabled default open in view property by adding spring.jpa.open-in-view=false to my application.properties which started giving me
Could not write JSON: failed to lazily initialize a collection of role error
我认为这是因为杰克逊正在对我的惰性加载对象调用吸气剂，所以我遵循了另一篇文章的说明，并为杰克逊添加了以下内容，以使惰性加载的集合不再存在:
I am assuming its because Jackson is calling the getters on my lazily loaded objects so I followed the instructions from another post and added the following for Jackson to leave the lazily loaded collections alone:
pom.xml
<dependency>
<groupId>com.fasterxml.jackson.datatype</groupId>
<artifactId>jackson-datatype-hibernate5</artifactId>
<version>2.9.9</version>
</dependency>
@Configuration
public class WebMvcConfig extends WebMvcConfigurerAdapter {
@Override
public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
for (HttpMessageConverter converter : converters) {
if (converter instanceof org.springframework.http.converter.json.MappingJackson2HttpMessageConverter) {
ObjectMapper mapper = ((MappingJackson2HttpMessageConverter) converter).getObjectMapper();
mapper.registerModule(new Hibernate5Module());
}
}
}
}
以上解决方案通过一对多"映射解决了该问题，但响应中仍关联了地址".
This solution above fixed the issue with the One to Many mapping but still has the Address associated in the response.
我不确定在这里可以做什么.默认登录页面上的用户实体不需要任何地址详细信息，因此我不想将其加载到登录页面上.当单击记录时，它将导航到另一页，这是我希望在响应中返回所有延迟加载的对象的地方.
I am not sure what can I do here. The User Entity on the default landing page does not need any address details so I do not want to load it on the landing page. When the record is clicked then it navigates to another page and that's where I would like all the lazy loaded objects to be returned in the response.
我已经尝试了所有可以在网上找到的内容，但到目前为止，仍然没有任何效果.我真的很感谢您的帮助.
I have tried everything I could find online but still nothing has worked so far. I would really appreciate some help with this.
正如一个用户提到的那样，它可能是另一个关于SO的问题的副本: 建议可能的重复项 我想提到的是，我通过禁用spring.jpa.open-in-view属性但添加了
As mentioned by one of the users that it might a duplicate of another question on SO: Suggested Possible duplicate I would like to mention that I got the Lazy loading working by disabling spring.jpa.open-in-view property but adding
mapper.registerModule(new Hibernate5Module());
带回与用户在响应中关联的地址.
brings back the address associated to the User in the response.
推荐答案
问题是杰克逊在编写JSON时会触发初始化，因此不要编写当前字段(地址).但是您不应该使用@jsonIgnore，因此在其他地方您可以返回Eager obj.
The problem is jackson triggering initialization when he writes the JSON, so just don't write the current field (address). But you should not use @jsonIgnore so at other places you could return an Eager obj.
您可以使用@jsonView批注，该批注可以在不同的请求下为同一obj提供不同的JSON.您可以看一下以下示例:
You can use the @jsonView annotation that can provide different JSON for the same obj at different requests. You can look this example :
创建视图类:
public class ViewFetchType {
static class lazy{ }
static class Eager extends lazy{ }
}
注释您的实体
@Entity
public class User {
@Id
@JsonView(ViewFetchType.Lazy.class)
private String id;
@JsonView(ViewFetchType.Eager.class)
@OneToOne( fetch = FetchType.LAZY)
private Address address ;
}
在控制器中指定FetchType类:
public class UserController {
private final UserRepository userRepository;
@Autowired
UserController(UserRepository userRepository) {
this.userRepository = userRepository;
}
@RequestMapping("get-user-details")
@JsonView(ViewFetchType.Eager.class)
public @ResponseBody Optional<User> get(@PathVariable String email) {
return userRepository.findByEmail(email);
{
@RequestMapping("get-all-users")
@JsonView(ViewFetchType.Lazy.class)
public @ResponseBody List<User> getUsers() {
return userRepository.findAll();
}
}
这是我从...中获得灵感的答案. https://stackoverflow.com/a/49207551/10162200
Here is the answer that i took the idea from... https://stackoverflow.com/a/49207551/10162200
这篇关于Spring Boot JPA-延迟加载不适用于一对一映射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！
