建立三个表之间的关系

Question

I am building Demo application in which we have three tables and i am using spring-boot data Jpa with mysql. I have following requirement

Table1 name->Student

sid sname srole //columns name

Table2 name->Courses

cid cname ctime //columns name

Table3 name-> Tutioncenter

id Name sid(student table sid) cid(Courses table cid)

@Entity
public class Student{

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long sid;
  private String sname;
  private String srole;

  //getter and setter
}

@Entity
public class Courses{

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long cid;
  private String cname;
  private String ctimme;

  //getter and setter
}

@Entity
public class Tutioncenter{

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

  private String name;

  @ManyToOne(fetch = FetchType.LAZY, optional = false)
  @JoinColumn(name = "sid", nullable = false)
  @OnDelete(action = OnDeleteAction.CASCADE)
  @JsonIgnore
  private Student student;

  @ManyToOne(fetch = FetchType.LAZY, optional = false)
  @JoinColumn(name = "cid", nullable = false)
  @OnDelete(action = OnDeleteAction.CASCADE)
  @JsonIgnore
  private Courses courses;

  //getter ans setter
}

@Repository
public interface CoursesRepository extends JpaRepository<Courses,Long>{}

@Repository
public interface StudentRepository extends JpaRepostiroy<Student,Long>{}

@Repository
public interface TutionRepository extends JpaRepository<Tutioncenter,Long>{

  Page<SecretManager> findBySIdAndCId(Long sId, Pageable pageable);
    
  Optional<SecretManager> findBySecretIdAndSIdAndCId(Long sid, Long cid);

}

Now I can design controller for Student and Courses but how should i design controller of Tutioncenter for crud operations??

Answer 1

The create, read, update operations of both student and courses table should be no relationship with tutioncenter table. Then we only need to consider how to deal with delete operation. Considering data in tutioncenter table, there would be 2 opotions:

1. Delete all related data in tutioncenter table at the same time.
2. Do not delete related data, or do not delete imediaterly.

The following are the SQL of delete both table together:

delete c, t from `courses` c join `tutioncenter` t on c.cid = t.cid where id = 1;

For tutioncenter table, I think there may be no update operation according to your business. Therefore we only need to focus on create, read, delete operations.

read operation is as following:

select s.sname, c.cname, c.ctime from `tutioncenter` t join `student` s on s.sid = t.sid join `courses` c on c.cid = t.cid;

delete operation is as following:

delete t from `tutioncenter` t join `student` s on s.sid = t.sid join `courses` c on c.cid = t.cid where t.sid = 1 and t.cid = 2;

insert operation as following:

insert into `tutioncenter` (name, sid, cid)
select 'test3', sid, cid from `student` s, `courses` c where s.sid = 1 and c.cid = 1;

Back to how to design your controller for TutionRepository , I think that should base on how to design your business. For example, If this demo system is designed only for student and administrator, then you need to consider both situations.

The following are what I could give till now how a student use your system:

1. Log in. With that said, all operation will have a sid now. Query student.
2. List all chozen courses. Query all courses have been choozen by this student.
3. If add new course, get all valid courses, then add chozen course. Query all courses operation. Add courses for this student.
4. Or delete chozen courses. Delete chozen courses.

To sum up, choosing courses system for student need the following interface:

1. Query student by name or id. url may be GET /students/<sid> or GET /students/<sname> . If you have login interface, you could use it instead.
2. Query all valid courses have been choozen by this student's id. GET /students/<sid>/courses
3. Query all valid courses. GET /courses
4. Add courses for this student (courses ids and student id). POST /students/<sid>/courses body is cid list like [cid1, cid2]
5. Delete courses for this student (courses ids and student id). DELETE /students/<sid>/courses/<cid>

The same to analysis what interfaces needed if you want to add a administrator role, who can manage courses and students.

Anyway, all should begin from business requirements.