How to update one to many relationship in laravel?

Question

I have a problem with updating the following table

And the data come from the view like below

this is my code

 foreach ($request->input('class_teacher') as $key=>$value){
                $class_teacher =ClassTeacher::where('class_id',$id);
                $class_teacher->class_id = $classes->class_id;
                $class_teacher->teacher_id =$value;
                $class_teacher->save();
            }

after the update I want it to be like this one

Answer 1

First delete the relationships, then recreate them all again.

 ClassTeacher::where('class_id',$id)->whereIn('teacher_id', $request->input('class_teacher'))->delete();
  
  foreach ($request->input('class_teacher') as $key=>$value){
    $class_teacher =new ClassTeacher;
    $class_teacher->class_id = $classes->class_id;
    $class_teacher->teacher_id =$value;
    $class_teacher->save();