記: Spring Data Jpa @OneToMany 級聯查詢被動觸發的問題

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

原文出處：https://www.cnblogs.com/ZhuChangwu/p/12158405.html