Question

我有一个班级Subject，

@Entity
@IdClass(SubjectId.class)
@Data
public class Subject {
    @Id
    private String name;
    @ManyToOne
    @JsonBackReference
    @Id
    private Teacher teacher;
    @OneToMany(mappedBy = "student")
    private List<StudentSubject> students;
}

其复合ID在SubjectId类中定义，

public class SubjectId implements Serializable{
    private String name;
    private Teacher teacher;

    public SubjectId(String name, Teacher teacher) {
        this.name = name;
        this.teacher = teacher;
    }
    SubjectId(){}
}

编译时，我收到错误

org.hibernate.MappingException：集合外键映射列数错误：com.example.Subject.students类型：component [name，teacher]

虽然这会将错误指向学生元素，但是在我删除了Subject的自动生成的ID之后发生了错误，并将其替换为名称和教师的组合。

无论如何，students元素在StudentSubject类中映射，

@Entity
@IdClass(StudentSubjectId.class)
public @Data
class StudentSubject {

    String studentId;
    @ManyToOne
    @Id
    private Subject subject;
    @ManyToOne
    @Id
    private Student student;

Answer 1

发生此错误时，通常意味着hibernate在正确数量的列上映射外键时出现问题。

在上面的情况中，subject类中的StudentSubject实体未被映射到两列，即name和teacher_email（这是Teacher表）。

要解决此类错误，请添加@JoinColumns，如下所示

class StudentSubject {
    @Id
    @ManyToOne
    @JoinColumns({
            @JoinColumn(referencedColumnName = "name"),
            @JoinColumn(referencedColumnName = "teacher_email") })
    private Subject subject;
}

referencedColumnName指的是外表中列的名称。

Answer 2

尝试以这种方式设置OneToMany：

 @OneToMany(
    cascade = CascadeType.ALL, 
    orphanRemoval = true)
    private List<StudentSubject> students = new ArrayList<>();

org.hibernate.MappingException：集合外键映射的列数错误

2 个答案: