I have encountered a bug in using Spring Data Jpa. Specifically,when @OneToMany was used to maintain a one-to-many relationship, lazy loading was effective.However,it may passively trigger the cascading query without using the cascading property.
My development environment :
<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.1.11.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent>
**My User.class is as follows **
**My Paper.class is as follows **
My PaperService.class is as follows
My UserController.class is as follows
I would like to use Jpa's @OneToMany default lazy loading mechanism when pagination queries was produced. Additionally, I don't need the collection of papers fields associated with the user.Nevertheless,I find that the papers attribute in the user is still populated with data in the returned results.
Therefore, I conducted the following debugging:**
send a request
Observe the execution of the code:
As you can see, although the lazy loading of Jpa was normal, I found the papers values that needed to be populated by cascading queries in the response data
I guess the user's papers field in Page must have been used by the framework before the data was written back to the browser, so I started with the UserController and continued to trace the source code
Then I was found the following call: Jackson called paper's getter through reflection while serializing the data . in the package com. Fasterxml.
Jackson. Databind. Ser.
**That's why I get a response in which the paper property is populated with a value, right **
**Look at it this way, even though lazy loading of Jpa is in effect, cascading queries are triggered passively **
**Lazy loading is in effect, but the cascading query is still triggered passively, which is not the result we want, I wonder what you think about it **
- solution 1:
@RequestMapping(path = "/getUserByPage") public Page getUserByPage(@RequestParam Integer from, @RequestParam Integer limit, @RequestParam(required = false) String name) { Page<User> page = userService.getUserByPage(from, limit, name); page.getContent().forEach(user->{ user.setPapers(null); }); return page; }
- solution 2:
@JsonIgnore
**@JsonIgnore can handle this pretty well, so why not let @OneToMany have it? **
@JsonIgnore @OneToMany(mappedBy = "user", cascade = CascadeType.ALL,fetch = FetchType.LAZY) private Set<Paper> papers = new HashSet<>();
- solution 3:
We can get rid of the getters (papers), but if we do that, we can't use the property by ourselves
