提取和在Spring Data REST中更新延迟加载的许多字段 [英] Fetching & Updating lazy-loaded many-many fields in Spring Data REST

问题描述

如何正确显示延迟加载许多字段，以便用户可以GET/PATCH/POST/DELETE许多Spring Data REST中有很多实体关系?

How do I correctly expose lazy-loaded many-many fields so that users can GET/PATCH/POST/DELETE many-many entity relationships in Spring Data REST?

例如，给定Student实体和Teacher实体之间存在多对多关系，并具有以下POJO:

For example, given a Student entity and Teacher entity bound by a many to many relationship, with the following POJOs:

@Entity
public class Teacher { // owner of bidirectional relationship
    @Id
    private int id;
    private String name;
    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "teacher_student",
            joinColumns = @JoinColumn(name = "teacher_id"),
            inverseJoinColumns = @JoinColumn(name = "student_id"))
    private Set<Student> students;

    // Constructor, getters/setters...
}

@Entity
public class Student {
    @Id
    private int id;
    private String name;
    @ManyToMany(mappedBy = "students", fetch = FetchType.LAZY)
    private Set<Teacher> teachers;

    // Constructor, getters/setters...
}

为实体提供存储库:

@RepositoryRestResource(path = "teacher")
public interface TeacherRepository extends CrudRepository<Teacher, int> {}

// similar repository for student

当我将GET发送到localhost:8080/teacher时，我得到了:

When I send a GET to localhost:8080/teacher, I get:

"_embedded": {
    "teacher": [
        {
        "name": "Bill Billie",
        "_links": {
            "self": { "href": "http://localhost:8080/teacher/1" },
            "teacher": { ... },
            "students": { "href": "http://localhost:8080/teacher/1/students" }
        }},
        (more teachers here...)
    ]
}
...

但，当我尝试GET来 http://localhost :8080/teacher/1/学生，尽管老师"Bill Billie" 确实有一个与他相关的学生，但我还是得到 404未找到数据库.

BUT, when I try a GET to http://localhost:8080/teacher/1/students, I get a 404 Not Found, even though the teacher "Bill Billie" does have a student associated with him in the database.

有趣的是，如果将FetchType更改为FetchType.EAGER，一切正常，我可以执行预期的GET，PATCH等.这有什么用?也许是一个错误，还是我搞砸了?

Interestingly, if I change the FetchType to FetchType.EAGER, everything works fine and I can perform the expected GET, PATCH, etc. What gives? Is this a bug, perhaps, or am I screwing something up?

tl; dr延迟获取无法正确显示很多关系，但是渴望获取可以很好地工作.我该如何懒惰地抓取它?

编辑:如果有关系，我将使用Spring 4.2.6和Spring Boot 1.3.5，并使用OpenJPA 2.4.1作为我的JPA提供程序.

Edit: If it matters, I am using Spring 4.2.6 with Spring Boot 1.3.5, and OpenJPA 2.4.1 as my JPA provider.

推荐答案

尝试使RestResources具有事务性.

Try making your RestResources transactional.

用@Transactional

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