Btukfyl

i am learning django and I am working on an project to make a pizza ordering portal.

I decided to make models for Toppings and Pizza seperately, so that more toppings can be added later and for pizza to of them can be selected, but I cannot seem to figure out the relation schema that should be used to link these two.

I stumbled upon Foreign key method but that is not I want
Here is the part of code for models:

class Topping(models.Model):

name = models.CharField(max_length = 30)



def __str__(self):

    return self.name



class Pizza(models.Model):

    name = models.CharField(max_length=40)

    first_toppping = models.Topping()

    second_topping = models.Topping()

    # in inches

    size = models.IntegerField(max_length=3)

    price = models.FloatField()

Please, suggest a method to link these two.

Given that a Pizza has two Toppings, you should add two ForeignKeys to Topping:

from django.utils.translation import gettext_lazy as _



class Topping(models.Model):

    # ...

    pass



class Pizza(models.Model):

    name = models.CharField(max_length=40)

    first_toppping = models.ForeignKey(

        Topping,

        on_delete=models.DO_NOTHING,

        related_name='pizza_first'

    )

    second_topping = models.ForeignKey(

        Topping,

        on_delete=models.DO_NOTHING,

        related_name='pizza_second'

    )



    size = models.IntegerField(max_length=3)

    price = models.FloatField()



    def clean(self):

        # given we want the two toppings to be different

        if self.first_topping_id == self.second_topping_id:

            raise ValidationError(_('Toppings should be different.'))

        return super(Pizza, self).clean()

or you can make the ForeignKeys nullable, such that if one of the toppings is NULL, this thus means that we do not select a first/second topping:

from django.utils.translation import gettext_lazy as _



class Topping(models.Model):

    # ...

    pass



class Pizza(models.Model):

    name = models.CharField(max_length=40)

    first_toppping = models.ForeignKey(

        Topping,

        on_delete=models.SET_NULL,

        null=True,

        related_name='pizza_first'

    )

    second_topping = models.ForeignKey(

        Topping,

        on_delete=models.SET_NULL,

        null=True,

        related_name='pizza_second'

    )



    size = models.IntegerField(max_length=3)

    price = models.FloatField()



    def clean(self):

        # given we want the two toppings to be different

        if self.first_topping_id is not None and self.second_topping_id is not None and self.first_topping_id == self.second_topping_id:

            raise ValidationError(_('Toppings should be different.'))

        return super(Pizza, self).clean()

Here we thus model that a pizza links twice to a topping.

Depending on the the application, you might want to allow a user to pick an arbitrary number of toppings, and sometimes it is even possible to pick the same topping multiple times.

We can use a ManyToManyField [Django-doc] for that, and in case we want to be able to add the same topping twice (or more) we can work with a through table, like:

# a pizza can have the same topping multiple times



class Topping(models.Model):

    # ...

    pass



class PizzaTopping(models.Model):

    pizza = models.ForeignKey('Pizza')

    topping = models.ForeignKey(Topping)



class Pizza(models.Model):

    name = models.CharField(max_length=40)

    toppping = models.ManyToManyField(

        Topping,

        through=PizzaTopping,

        related_name='pizzas'

    )



    size = models.IntegerField(max_length=3)

    price = models.FloatField()

If I understand you correcyly, each pizza has many toppings, so you have to use many to many. This way, you can add as many toppings as you want (0-*)

class Topping(models.Model):

    name = models.CharField(max_length = 30, unique = True)



    def __str__(self):

        return self.name



class Pizza(models.Model):

    name = models.CharField(max_length=40)

    toppings = models.ManyToManyField(Topping)

    # in inches

    size = models.IntegerField(max_length=3)

    price = models.FloatField()

As you can see in the following example, I create a pizza object and I add as many toppings as I want :

pizza = Pizza(name="CheesePizza",size=5,price=25.22)

pizza.save()



topping1 = Topping(name="chocolate")

topping1.save()

topping2 = Topping(name="whataver")

topping2.save()

topping3 = Topping(name="component")

topping3.save()



pizza.toppings.add(topping1,topping2,topping3)