Duplicate or Null error when trying to send POST request for JSON Object with Foreign Key using Spring JPA - spring

Question

Here's my parent entity:
#Entity(name = "DrivingInstructor")
#Table(name = "driving_instructor")
#Getter
#Setter
#NoArgsConstructor
public class DrivingInstructor {
#Id
#Column(name = "driving_instructor_id")
private long drivingInstructorId;
#Column(name = "driving_instructor_name")
#Size(max = 128)
private String drivingInstructorName;
#Column(name = "specialization")
#Size(max = 200)
private String specialisation;
}
And here's my supposed child entity:
#Entity(name = "DrivingStudent")
#Table(name = "driving_student")
#Getter
#Setter
#NoArgsConstructor
public class DrivingStudent {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "driving_student_id")
private long drivingStudentId;
#Column(name = "driving_student_name")
#Size(max = 128)
private String drivingStudentName;
#ManyToOne(cascade = CascadeType.ALL, targetEntity = DrivingInstructor.class)
#JoinColumn(name = "driving_instructor_id", referencedColumnName = "driving_instructor_name", insertable = false, updatable = false)
private DrivingInstructor drivingInstructor;
}
Here's the relevant chunk of my service class for inserting/saving an instance of a DrivingStudent into the database:
#RequestMapping(path = "api/v0/driving-school")
#RestController
#AllArgsConstructor
public class DrivingStudentRestController {
private final DrivingStudentServiceImpl drivingStudentServiceImpl;
#PostMapping
Long insertOrUpdateDrivingStudent(#Valid #RequestBody DrivingStudent drivingStudent) {
return drivingStudentServiceImpl.insertOrUpdateDrivingStudent(drivingStudent);
}
}
DrivingStudentServiceImpl is just an abstraction layer for Repository class that extends JpaRepository<DrivingStudent, Long>, so insertOrUpdateDrivingStudent() is practically just using the save() method from CrudRepository.
An instance of DrivingInstructor is already pre-inserted with drivingInstructorId of 1, and so I tried to execute a POST request via Postman using this JSON object:
{
"drivingStudentName": "Peter Parker",
"drivingInstructor": {"drivingInstructorId": 1}
}
And I'm getting this exception:
2021-08-27 20:03:37.554 ERROR 16108 --- [nio-8080-exec-3] o.h.engine.jdbc.spi.SqlExceptionHelper :
ERROR: duplicate key value violates unique constraint "driving_instructor_pkey"
Detail: Key (driving_instructor_id)=(1) already exists.
2021-08-27 20:03:37.590 ERROR 16108 --- [nio-8080-exec-3] o.a.c.c.C.[.[.[/].[dispatcherServlet] :
Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception
[Request processing failed; nested exception is
org.springframework.dao.DataIntegrityViolationException:
could not execute statement; SQL [n/a];
constraint [driving_instructor_pkey];
nested exception is org.hibernate.exception.ConstraintViolationException:
could not execute statement] with root cause
org.postgresql.util.PSQLException: ERROR: duplicate key value violates unique constraint "driving_instructor_pkey"
Detail: Key (driving_instructor_id)=(1) already exists.
I also tried revising my RestController's PostMapping to look like this, but still nothing changes:
#RequestMapping(path = "api/v0/driving-school")
#RestController
#AllArgsConstructor
public class DrivingStudentRestController {
private final DrivingInstructorRepository drivingInstructorRepository;
private final DrivingStudentServiceImpl drivingStudentServiceImpl;
#PostMapping
Long insertOrUpdateDrivingStudent(#Valid #RequestBody DrivingStudent drivingStudent) {
Optional<DrivingInstructor> drivingInstructor = drivingInstructorRepository.findById(drivingStudent.getDrivingInstructor().getDrivingInstructorId());
if (drivingInstructor.isPresent()) {
drivingStudent.setDrivingInstructor(drivingInstructor.get());
return drivingStudentServiceImpl.insertOrDrivingStudent(drivingStudent);
}
return null;
}
}
The error I am getting then changed to:
2021-08-27 21:36:58.622 ERROR 11388 --- [nio-8080-exec-4] o.h.engine.jdbc.spi.SqlExceptionHelper :
ERROR: null value in column "driving_instructor_number" of relation "driving_student" violates not-null constraint
Detail: Failing row contains (Peter Parker, null).
2021-08-27 21:36:58.632 ERROR 11388 --- [nio-8080-exec-4] o.a.c.c.C.[.[.[/].[dispatcherServlet] :
Servlet.service() for servlet [dispatcherServlet] in context with path []
threw exception [Request processing failed;
nested exception is org.springframework.dao.DataIntegrityViolationException:
could not execute statement; SQL [n/a];
constraint [driving_instructor_number" of relation "driving_student];
nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement] with root cause
org.postgresql.util.PSQLException: ERROR: null value in column "driving_instructor_number" of relation "driving_student" violates not-null constraint
Detail: Failing row contains (Peter Parker, null).
There are stuff I've tried but most exceptions simply end up with either of those two. All I really wanted to do was insert an instance of DrivingStudent into the database using POST request, with a foreign key connecting it to a DrivingInstructor instance, and then of course, be able to retrieve those data.
I am able to do insert data manually into the database using the statement:
INSERT INTO driving_student VALUES ('Peter Parker', 1);
And I am able to retrieve that data in JSON format using GET method. So far, my only problem really is how to deal with the POST method.

Answer 1

Ok, I just changed/simplified the annotations in DrivingStudent's drivingInstructor JoinColumn field from this:
#ManyToOne(cascade = CascadeType.ALL, targetEntity = DrivingInstructor.class)
#JoinColumn(name = "driving_instructor_id", referencedColumnName = "driving_instructor_name", insertable = false, updatable = false)
private DrivingInstructor drivingInstructor;
to this:
#ManyToOne
#JoinColumn(name = "driving_instructor_id")
private DrivingInstructor drivingInstructor;
and it somehow worked... I have no idea why though.