JPA Hibernate@ManyToone外键约束失败

Question

我正在做一个基本的例子来测试级联删除操作，但我得到了异常。这是我的实体

@Table(name = "project")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Project implements Serializable {

    private static final long serialVersionUID = 1L;

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

    @Column(name = "project_name")
    private String projectName;

    @ManyToOne(cascade = CascadeType.REMOVE)
    private Student student;

    ...
} 

@Entity
@Table(name = "student")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Student implements Serializable {

    private static final long serialVersionUID = 1L;

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

    @Column(name = "name")
    private String name;
 
    ...
}

Caused by: java.sql.SQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`document_control`.`project`, CONSTRAINT `FKjvi932wdxw4ux6m7u6abiy7qv` FOREIGN KEY (`student_id`) REFERENCES `student` (`id`))

@DeleteMapping("/students/{id}")
    public ResponseEntity<Void> deleteStudent(@PathVariable Long id) {
        log.debug("REST request to delete Student : {}", id);
        studentRepository.deleteById(id);
        return ResponseEntity
            .noContent()
            .headers(HeaderUtil.createEntityDeletionAlert(applicationName, false,
                ENTITY_NAME, id.toString()))
            .build();
    }

Answer 1

从父级到子级的级联移除操作将需要从父级到子级的关系（而不仅仅是相反的关系，这似乎是您目前所拥有的）。话虽如此，试着创建一个双向关系，如下所示：

@Entity
@Table(name = "student")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Student implements Serializable {

    private static final long serialVersionUID = 1L;

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

    @Column(name = "name")
    private String name;
 
    @OneToMany(mappedBy = "student", cascade = CascadeType.REMOVE)
    private Set<Project> projects;
}

此外，请考虑从项目中删除级联删除操作，否则您可能会在删除项目时删除学生。