Set a limit for forms with the same value Django - django

Question

So what I want to do is to set a limit of forms with the same value. There are different activities from a foreign model to which students can apply.
I have name(naam), student number(studentnummer), activity(activiteit) and class(klas), and I want to set a limit of 10 forms with the same activity (max of people who can do the same activity) and a limit of 1 for student number (so students can only apply for one activity).
models.py
class Klas(models.Model):
klas = models.CharField(max_length=8)
def __str__(self):
return f"{self.klas}"
class Activiteit(models.Model):
titel = CharField(max_length=64)
docent = CharField(max_length=32)
icon = models.ImageField()
uitleg = models.TextField()
def __str__(self):
return f"{self.id}:{self.titel}:{self.docent}"
class Aanmelden(models.Model):
naam = CharField(max_length=32)
studentnummer = IntegerField()
klas = ForeignKey(Klas, on_delete=models.CASCADE, default=None, blank=True)
activiteit = ForeignKey(Activiteit, on_delete=models.CASCADE, default=None, blank=True)
def __str__(self):
return f"{self.id}:{self.naam}:{self.studentnummer}"
views.py
def home(request):
activiteiten = Activiteit.objects.all()
form = AanmeldenForm()
if request.method == 'POST':
form = AanmeldenForm(request.POST)
if form.is_valid():
form.save()
return render(request, 'home.html', {
'activiteiten': activiteiten,
'form':form,
})
forms.py
class AanmeldenForm(forms.ModelForm):
class Meta:
model = Aanmelden
fields = (
'naam','studentnummer','klas','activiteit'
)
If you know how to solve this or have a better idea of doing this kind of system please let me know.
Thanks in advance!!

Answer 1

You probably need to have a variable inside your Aktiviteit class, such as plaatsen_beschikbaar that is initialised at 10 when you create a new instance of an Aktiviteit. Then on successful Aanmelden to an instance you reduce it by one. You need to make sure in your model that plaatsen_beschikbaar cannot be less than zero, and if someone deletes the aanmelding then increase the variable by 1. Edit: or you use a validator such as the one below to restrict Aanmelden. You could also make your model have a #property that returns the plaatsen_beschikbaar instead of using a field. On second thought, this seems like a better plan, hence this edit
To make sure a student may only have 1 Aanmelden, you could just make your studentnummer unique in your Aanmelden class. But that makes your model not future-proof if you decide in future that students may subscribe to two or three activities. In that case you need to have a foreign key relationship to Student and restrict the number of Aanmelden that a student may have using a validator like so for instance
def beperk_aanmelden(value):
if Aanmelden.objects.filter(student_id=value).count() >= 1:
raise ValidationError('Student heeft al de maximale aanmeldingen')
else:
return value
Then in your Aanmelden model:
student = ForeignKey(Student, validators=[beperk_aanmelden,])
Edit: based on your current model it would look like this:
def beperk_aanmelden(value):
if Aanmelden.objects.filter(studentnummer=value).count() >= 1:
raise ValidationError('Student heeft al de maximale aanmeldingen')
else:
return value
And in your model:
studentnummer = IntegerField(validators=[beperk_aanmelden,])
Edit 2:
To check the plaatsen_beschikbaar you could do something like this:
def beperk_activiteit(value):
if Activiteit.objects.get(activiteit_id=value).plaatsen_beschikbaar <= 0:
raise ValidationError('Activiteit heeft geen plaatsen beschikbaar meer! Kies een andere activiteit.')
Then for the field in your model:
activiteit = ForeignKey(Activiteit, on_delete=models.CASCADE, default=None, blank=True, validators=[beperk_activiteit,])
Edit 3:
For the plaatsen_beschikbaar I would do something like this. Each Activiteit has a capaciteit where you set the maximum places available. Then define an #property, which gives you a non-db calculated field which you can access just like a normal field. The difference is that it's not stored, but re-calculated each time you access it. Inside count the number of Aanmelden that have the Activiteit instance as related object. That's your number of already booked placed. Then subtract this from capaciteit and you'll have a current plaatsen_beschikbaar
class Activiteit(models.Model):
titel = CharField(max_length=64)
docent = CharField(max_length=32)
icon = models.ImageField()
uitleg = models.TextField()
capaciteit = models.IntegerField()
#property
def plaatsen_beschikbaar(self):
geboekt = Aanmelden.objects.filter(activiteit_id=self.id).count()
return self.capaciteit - geboekt
def __str__(self):
return f"{self.id}:{self.titel}:{self.docent}"