Question

I have the following models:

class City(models.Model):
    name = models.CharField(max_length=100)

class Pizza(models.Model):
    name = models.CharField(max_length=100)
    cities = models.ManyToManyField('City')

class Price(models.Model):
    cad = models.DecimalField()
    usd = models.DecimalField()
    pizza = models.ForeignKey(Pizza)

I can create a brand new pizza with the following code:

new_pizza = Pizza(name='Canadian')
new_pizza.save()
# I already calculated the following before, the syntax might not 
# be correct but that's how you see it from the shell
new_pizza.cities = [<City: Toronto>, <City: Montreal>]
new_pizza.save()
new_price = Price(cad=Decimal('9.99'), usd=Decimal('8.99'), pizza=new_pizza.id)
new_price.save()

I might have some typo here and there but the above works fine but I just don’t like saving the objects so many times. Is there a better way to create a Pizza object from scratch with the current models above?

Answer 1

You can use the Model.objects.create method, which creates a new instance, saves it and returns a pointer to the new object, ready to define relationships to other instances.

#create a new Pizza
#There's no need to explicitly save the new Pizza instance
new_pizza = Pizza.objects.create(name='Canadian')

#Add Cities to Pizza
#Here, Toronto and Montreal are City instances you created earlier
#There's no need to save new_pizza after adding cities
new_pizza.cities.add(Toronto, Montreal)

#Create a new Price object for new_pizza
#There's no need to explicitly save new_pizza or the new Price instance.
new_pizza.price_set.create(usd=Decimal('8.99'),cad=Decimal('9.99'))

Note that by defining the pizza ForeignKey in the Price model, a Pizza can have more than one Price. Is this what you meant? Defining a price ForeignKey in Pizza would give one price per Pizza.