JPA - 字段必须与引用的主键具有相同的列数

Question

在我的项目中，我有两个班级： School和Teacher 。 一所学校可以指派多名教师。 到目前为止，这是我的代码：

@Entity
@Table(name = "schools", uniqueConstraints = {
    @UniqueConstraint(columnNames = {
            "name"
    }})
public class School {

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

...

@OneToMany(fetch = FetchType.LAZY)
@JoinTable(name = "teachers",
        joinColumns = @JoinColumn(name = "school_id"),
        inverseJoinColumns = @JoinColumn(name = "teacher_id"))
private Set<Teacher> teachersList = new HashSet<>();

另一个类如下所示：

@Entity
@Table(name = "teachers", uniqueConstraints = {
    @UniqueConstraint(columnNames = {
            "id"
    })
})
public class Teacher {

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

...

现在，当我尝试构建此项目时，出现错误：

org.hibernate.MappingException: Foreign key (FK4hetjkgnpo354f7uwax5aewc0:teachers
 [teacher_id])) must have same number of columns as the
referenced primary key (teachers [school_id,teacher_id])

我迷路了。 我到底错过了什么？ 谢谢！

Answer 1

@JoinTable 用于 ManyToMany 关系，您必须在Many Entity 端（Teachers）中使用 @JoinColumn

尝试这个：

public class Teacher{
//...

@ManyToOne
@JoinColumn(name="fk_school_id") // this is your foreign key in your Teacher table of your DB
private School school;

}

但是，如果您还想检索每所学校的教师列表，则必须将其放入您的单一实体（学校）中：

@OneToMany(mappedBy="school")
private List<Teacher> teachers = new ArrayList();