Django - how to write off quantity from one model to another?

Question

Django

Hello!
There is a model:

class Material(models.Model):
    name = models.CharField("Материал:", max_length=100)
    coming = models.IntegerField(u"Приход Кол-во")
    balance = models.IntegerField(u"Остаток Кол-во")

class Plot(models.Model):
    plot = models.CharField("Участок:", max_length=100)
    material = models.ForeignKey(Material, verbose_name=u"Материал")
    expenditure = models.IntegerField(u"Израсходование Кол-во Материала")

    def amount(self):
        try:
            calculation = ((self.material.coming) - (self.expenditure))
            return "%d" % calculation
        except:
            return False

@receiver(pre_save, sender=Plot)
def total(sender, instance, **kwargs):
    instance.material.balance = instance.calculation()

Task, there is a Material model, with the quantity of the arrival of the Material, let's say 10 pcs. There is a Plot model, where the material consumption is indicated, it is necessary to write off exactly the material that was selected in the Plot model, if the material is written off more than it is in the form, this is indicated in the form. The balance of the material is indicated in the Material model in the balance field.
Maybe in the form to produce a reduction in quantity?
Thank you!

Answer 1

ay