How to display multiple related objects in Django

Question

I have two models that look like this:

class EventDrink(models.Model):
    name = models.CharField(max_length=255)
    drink_active = models.BooleanField()

    def __str__(self):
        return self.name


class EventIngredient(models.Model):
    drink = models.ManyToManyField(EventDrink)
    name = models.CharField(max_length=255)
    url = models.URLField()

    def __str__(self):
        return self.name

I now want to display all drinks with drink_active set to True to display in my view. I also want to display the ingredients related to that drink. I know I can filter on the drinks in my view like this:

drinks = EventDrink.objects.filter(drink_active=1)

But how do I now display the ingredients related to each drink?

Answer 1

You can access the related ones with:

my_drink.eventingredient_set.all()

this will trigger a query to fetch the related EventIngredients. If we have to do that for several drinks that is not very efficient. We can use .prefetch_related(…) ^[Django-doc] to batch all these requests in one additional query, so:

drinks = EventDrink.objects.filter(drink_active=True).prefetch_related(
    'eventingredient_set'
)

We can then for example enumerate over the drinks and their ingredients:

for drink in drinks:
    print(drink.name)
    for ingredient in drink.eventingredient_set.all():
        print(f' - {ingredient.name}')
    print()