How to pull out the total price from this “self.gifts.all()” with one request?

Question

Django

There are three models, each has a price field

class Tomato(models.Model):
    price=...
class Potatoes(models.Model):
    price=...
class Eggplant(models.Model):
    price=...

And there is a 4th model:

class Vegetable(models.Model):
    tomato = models.OneToOneField(Tomato, verbose_name='Томат', on_delete=models.CASCADE, blank=True, null=True)
    potatoes = models.OneToOneField(Potatoes, verbose_name='Potatoes', on_delete=models.CASCADE, blank=True, null=True)
    eggplant = models.OneToOneField(Eggplant, verbose_name='Eggplant', on_delete=models.CASCADE, blank=True, null=True)
    gifts = models.ManyToManyField('self', blank=True, symmetrical=False)

How to get the total price from this (self is Vegetable) "self.gifts.all()" with one query?
The problem is that ANY instance of vegetable should and only contains one thing:

print vegetable.tomato, vegetable.potatoes, vegetable.eggplant
.... "Tomato-delicious", none, none

gifts of course, contains links to several instances of Vegetable, how to get the sum of the price of these instances?

Answer 1

That's how you can. Just google for select and prefetch_related for self.gifts.all()

class Vegetable(models.Model):
    tomato = models.OneToOneField(Tomato, verbose_name='Томат', on_delete=models.CASCADE, blank=True, null=True)
    potatoes = models.OneToOneField(Potato, verbose_name='Potatoes', on_delete=models.CASCADE, blank=True, null=True)
    eggplant = models.OneToOneField(Eggplant, verbose_name='Eggplant', on_delete=models.CASCADE, blank=True, null=True)
    gifts = models.ManyToManyField('self', blank=True, symmetrical=False)

    @property
    def get_price(self):
        tomato = self.tomato.price if self.tomato is not None else 0
        potatoes = self.potatoes.price if self.potatoes is not None else 0
        eggplant = self.eggplant.price if self.eggplant is not None else 0
        return sum([tomato, potatoes, eggplant])
        
    @property   
    def get_gift_price(self):
        return sum([x.get_price for x in self.gifts.all()])