Question

So basically my app has users of course and each user can create 5 instances of “ModelA”. Simple enough, but there is also “ModelB” with a relation to “ModelA” and the user model. I want the user to be able to create a total of 15 “ModelB” instances, but each “ModelA” instance can only have 5 “ModelB” instances tied to it?

Any tips?

The way I handle the first part for 5 “ModelA” instances per user is like this:

def clean(self):
        new_instance = self.__class__
        if (new_instance.objects.count() > 4):
            raise ValidationError(
                "Users may only create 5 %s." % new_instance.verbose_name_plural
            )
        super(ModelA, self).clean()

Thanks

EDIT:(Built in Django Users functionality assumed)

class ModelB(models.Model):
    user = models.ForeignKey(User)
    modelA = models.ForeignKey('ModelA')
    other_field = models.CharField(max_length=50)

class ModelA(models.Model):
    user = models.ForeignKey(User)
    other_field = models.CharField(max_length=50)

Basically The user can create 5 ‘ModelA’ instances and for each of those instances they can create 3 ‘ModelB’ instances.

How can I do this within the model logic?

thanks

Answer 1

Does this work?

class ModelB(models.Model):
  user = models.ForeignKey(User)
  modelA = models.ForeignKey('ModelA', related_name = 'modelbs')
  other_field = models.CharField(max_length=50)

  def clean(self):
    if (self.modelA.modelbs.all().count() > 2):
        raise ValidationError(
            "ModelA may create may only create 3 modelBs "
        )
    super(ModelB, self).clean()


class ModelA(models.Model):
  user = models.ForeignKey(User, related_name = 'modelas')
  other_field = models.CharField(max_length=50)

  def clean(self):
    if (self.user.modelas.all().count() > 2):
        raise ValidationError(
            "User may create may only create 3 modelAs "
        )
    super(ModelA, self).clean()