[FIXED] How can I calculate discount fields from another table's fielsd

Issue

I have a model like this:

class InvoiceItem(models.Model):
   book = models.ForeignKey(Book, on_delete=models.PROTECT)
   invoice = models.ForeignKey(Invoice, on_delete=models.PROTECT, related_name='items')
   title = models.CharField(max_length=100, null=True, blank=True)
   price = models.IntegerField(null=True, blank=True)
   discount = models.IntegerField(blank=True, default=0)
   totalprice = models.IntegerField(null=True, blank=True)
   count = models.IntegerField(null=True, blank=True)

and I want to calculate discount from book's discount table How can I do it? should I calculate it in models?

Solution

Here we can create property for override models fields like this (without override save() method)

class InvoiceItem(models.Model):
    book = models.CharField(max_length=100)
    invoice = models.PositiveIntegerField()
    title = models.CharField(max_length=100, null=True, blank=True)
    og_price = models.IntegerField(null=True, blank=True)
    sell_price = models.IntegerField(null=True, blank=True)
    discount = models.IntegerField(blank=True, default=0)
    discounted_price = models.IntegerField(blank=True, default=0)
    count = models.IntegerField(null=True, blank=True)

    @property
    def discounted_price(self):
        return ((self.og_price*self.discount)/100)

    @property
    def sell_price(self):
        return ((self.og_price - self.discounted_price))

with override save() method

class InvoiceItem(models.Model):
    book = models.CharField(max_length=100)
    invoice = models.PositiveIntegerField()
    title = models.CharField(max_length=100, null=True, blank=True)
    og_price = models.IntegerField(null=True, blank=True)
    sell_price = models.IntegerField(null=True, blank=True)
    discount = models.IntegerField(blank=True, default=0)
    discounted_price = models.IntegerField(blank=True, default=0)
    count = models.IntegerField(null=True, blank=True)

    @property
    def dis_price(self):
        print((self.og_price*self.discount)/100)
        return ((self.og_price*self.discount)/100)

    @property
    def selling_price(self):
        print(self.og_price - self.dis_price)
        return (self.og_price - self.dis_price)

    def save(self, *args, **kwargs):
        self.sell_price = self.selling_price
        self.discounted_price = self.dis_price
        super(InvoiceItem, self).save(*args, **kwargs)

Output

You need to fill only those fields

NOTE: here i changed two fields for data adding in database

book = models.CharField(max_length=100)
invoice = models.PositiveIntegerField()

Answered By - Mahammadhusain kadiwala