与条件的多对一关系

Question

我有两张表，student 和 teacher，关系为 ManyToOne。表结构如下

student(
    id long,
    student_id string,
    ....
    teacher_id string,
    active boolean
)

teacher(
    id long,
    teacher_id string,
    ....
    active boolean
)

我正在使用 Spring Boot 和 Hibernate。此处更新实体时，表中现有行的活动列将设置为 false，并且将添加一个新行，并使用新的 id(long) 和活动为 true。这就是为什么每个表中有两个 id 值。这里的问题是我已经在我的实体中指定了学生与教师的关系，外键为teacher_id。

@Entity
@Table(name = "student")
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "student_id")
    private String studentId;

    @ManyToOne
    @JoinColumn(name = "teacher_id", referencedColumnName = "teacher_id")
    private Teacher teacher;

    @Column(name = "active")
    @JsonIgnore
    private Boolean active = true;
}

@Entity
@Table(name = "teacher")
public class Teacher {

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

    @Column(name = "teacher_id")
    private String teacherId;

    @OneToMany(mappedBy = "teacher")
    private Set<Student> students = new HashSet<>();

    @Column(name = "active")
    @JsonIgnore
    private Boolean active = true;
}

但是由于可以使用相同的teacher_id 出现多个教师，因此失败了。有没有办法给关系提供条件以获取 active 为 true 的老师？在表中，将只有一位具有给定 id 且 active 为 true 的教师。

Answer 1

Teacher 实体中不应有 teacher_id 外键字段。相反，只需使用主键 id 列。考虑这个版本的实体：

@Entity
@Table(name = "student")
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "student_id")
    private String studentId;

    @ManyToOne
    @JoinColumn(name = "teacher_id", referencedColumnName = "id")
    private Teacher teacher;

    @Column(name = "active")
    @JsonIgnore
    private Boolean active = true;
}

@Entity
@Table(name = "teacher")
public class Teacher {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @OneToMany(mappedBy = "teacher")
    private Set<Student> students = new HashSet<>();

    @Column(name = "active")
    @JsonIgnore
    private Boolean active = true;
}

这种设计应该强制一个给定的学生只能与一个老师相关联（尽管一个给定的老师可以有多个学生）。