Get values from second table by ID that is in first table-CodePudding

So i have grades controller, and i want to display table that will show students first name, students last name and then grades from table grades. I linked grades by grades_id in students so that every student has their own grades.

Problem is, i cant figure out how to make it work.

@GetMapping("/grades")
public String grades(Model theModel){

    List<students> theStudents = studentService.findAll();
    List<grades> theGrades = null;

    for(students s : theStudents){

        theGrades = (List<grades>) gradesService.findById(s.getGrades_id());


    }

    theModel.addAttribute("grades",theGrades);
    theModel.addAttribute("students",theStudents);

    return "/ediary/principal/grades";
}

  public grades findById(int theId) {

    Optional<grades> result = gradesRepository.findById(theId);

    grades theGrades = null;

    if(result.isPresent()){
        theGrades = result.get();
    } else{
        throw new RuntimeException("Did not find grade id - "   theId);
    }

    return theGrades;
}

I tried something like this, but its obviously not working,

so the main thing im trying is this:

How do i do this?

CodePudding user response：

Instead of returning Optional from findById() return List and instead of findById() write findAllById() inside the findById().
for example

    List<grades> result = gradesRepository.findAllById(theId);

CodePudding user response：

I think you might reconsider your conception , you can achieve that easily if you did Student have a list of grades and the Grade entity is the owner of the relationship in terms of holding the primary key of the Student entity as a foreign key , and then when you fetch the Student you can get every Grade object associated with it.