I have Student, Class and StudentClass models. I would like a student to be able to join a new class by inputting the class_code into a form. To join a class the user's student_id and the class_code is saved to the StudentClass model. The student_id isn't a form field so should be obtained by querying the Student model with the logged-in user's username and returning the student_id.

models.py:

class StudentClass(models.Model):
    class Meta:
        unique_together = (('class_code', 'student_id'),)
    class_code = models.ForeignKey(Class, on_delete=models.CASCADE)
    student_id = models.ForeignKey(Student, on_delete=models.CASCADE)

forms.py:

class JoinClassForm(forms.ModelForm):
    class Meta:
        model = StudentClass
        fields = ['class_code']
        exclude = ('student_id',)

views.py

@login_required
def join_class(request):
    if request.method == "POST":
        joinclass_form = JoinClassForm(request.POST or None)
        if joinclass_form.is_valid():
            formclass_code = joinclass_form.data.get('class_code')
            if Class.objects.filter(class_code=formclass_code).exists():
                joinclass_form.save(commit=False)
                joinclass_form.student_id =
                Student.objects.filter(username=request.user.username).values_list('student_id', flat=True)
                joinclass_form.save()
                return redirect('assignments')
            else:
                messages.success(request, ("This class doesn't exist!"))
    else:
        joinclass_form = JoinClassForm
    return render(request, 'join_class.html', {'joinclass_form': joinclass_form})

I've tried using a hidden_field for student_id, excluding student_id from the form fields and saving as commit=False, and I've gotten the same error: IntegrityError Not NULL constraint failed. Is there an error in my code that I have missed or am I using the wrong method? Thanks in advance

Edit: Forgive me but copy-paste went kinda awry on the last set of code and I have no idea how to fix it

CodePudding user response：

you dont need to put .username at request.user. You can just say request.user

CodePudding user response：

Thanks everyone for your help but I managed to fix it now

In case anyone needs this in the future, I realised that I made 2 mistakes:

1. I wasn't saving my form correctly in my views.py, I was trying to save the value student_id to the form rather than an object.

https://docs.djangoproject.com/en/4.1/topics/forms/modelforms/#the-save-method

2. I named my foreign key in my StudentClass table as student_id which meant that Django was renaming it as student_id_id. To fix this, I just removed _id from student_id in the StudentClass table.