Question

每个人都对使用注释@OneToMany / @ManyToOne有疑问；是否可以在该模型中创建两套主题的用户模型（针对教师和参加学生的行为），而不用创建单独的学生模型和教师模型？我编写了这样的代码，但是当我想获取有关项目和用户的数据时，休眠会导致“堆栈溢出”错误崩溃。我将添加使用H2数据库的信息。

用户实体：

@Entity
public class User{
    @OneToMany(
            mappedBy = "student",
            cascade = CascadeType.ALL,
            fetch = FetchType.EAGER,
            orphanRemoval = true
    )
private Set<Item> items = new HashSet<>();

    @OneToMany(mappedBy = "teacher",
            cascade = CascadeType.ALL,
            fetch = FetchType.EAGER,
            orphanRemoval = true
    )
private Set<Item> carriedItems= new HashSet<>();
}
//id and other data

项目实体：

@Entity
public class Item{
    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "student_id", nullable = false)
    private User student;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "teacher_id", nullable = false)
    private User teacher;
}
//id and other data

感谢@Leviand

Answer 1

根据您的评论，您的代码和逻辑看起来需要一些返工。首先，使用两个专用的类代替Item pojo：

@Entity
@Table(name = Studend) // I'm guessing a table name
public class Student{
    @JoinColumn(name = "student_id", nullable = false)
    private User user;
}

@Entity
@Table(name = Teacher) // I'm guessing a table name
public class Teacher{
    @JoinColumn(name = "teacher_id", nullable = false)
    private User user;
}

然后，由于User仅可连接到单个Teacher或Student，因此请以类似的方式加以说明：

@Entity
@Table(name = User) // I'm guessing a table name
public class User{
    @OneToOne(
            mappedBy = "student",
            cascade = CascadeType.ALL,
            fetch = FetchType.EAGER,
            orphanRemoval = true
    )
    private Student student;

    @OneToMany(mappedBy = "teacher",
            cascade = CascadeType.ALL,
            fetch = FetchType.EAGER,
            orphanRemoval = true
    )
    private Teacher teacher;
}

希望这会有所帮助：）

休眠@OneToMany @ManyToOne映射

1 个答案: