spring boot hibernate双向映射多对一无法建立关系

Question

我有两个实体表，一个是类别，另一个是主题

我的类别实体

@Entity
public class Category extends AuditableEntity {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;

@Column(unique = true)
private String name;

@OneToOne(cascade = CascadeType.ALL)
@JoinColumn(name = "description_id")
private CategoryDescription description;

@OneToMany( mappedBy = "category", cascade = CascadeType.ALL, 
orphanRemoval = true)
private List<Subject> subjects;

//getter and setter
}

还有我的主题实体

@Entity
public class Subject extends AuditableEntity {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;

@Column(unique = true)
private String name;

@OneToOne(cascade = CascadeType.ALL)
@JoinColumn(name = "description_id")
private SubjectDescription description;

@ManyToOne(fetch = FetchType.EAGER)
private Category category;

//Getter and Setter
}

类别存储库

@Repository
@Transactional
public interface CategoryRepository extends 
JpaRepository<Category, Integer> {
}

主题库

@Repository
@Transactional
public interface SubjectRepository extends JpaRepository<Subject, 
Integer> {
}

类别控制器

@RestController
@RequestMapping("/category/api/")
public class CategoryResource {

private final CategoryService categoryService;
private final SubjectService subjectService;
private final TopicService topicService;

public CategoryResource(CategoryService categoryService, 
SubjectService subjectService, TopicService topicService) {
    this.categoryService = categoryService;
    this.subjectService = subjectService;
    this.topicService = topicService;
}

@PostMapping("save")
public void saveCategory(@RequestBody Category category) {

    categoryService.save(category);

}

我正在使用邮递员来保存数据。问题是在将数据保存到类别和主题表后，我的主题表列 category_id 为空，我无法在它们之间建立关系，我的 sql 结构和数据在保存数据后显示如下

分类表

主题表

category_id 为 NULL 如何设置类别 id 我尝试了很多方法但找不到解决方案。请帮我解决这个问题

Answer 1

你在学习spring boot真是太好了！

回答您的问题，因为答案很简单，您的代码缺少主题中的类别。

subject.setCategory(category);

现在这可能会导致您出现异常，因此请确保在保留主题之前保存类别。

干杯！