pythondjangodjango-models

Django model has ManyToMany field, how to get all IDs without fetching the objects?

I have a data structure like this:

class Pizza(models.Model):
    name = models.CharField(max_length=100)
    toppings = models.ManyToManyField(Topping, related_name="pizzas")

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

And to get all topping IDs related to a pizza I can do this:

list(map(lambda t: t.id, pizza.toppings.all()))

But this fetches all toppings completely from the database, even thought I only need the IDs. Is there a way to get the IDs without fetching the complete objects (for performance reasons)?

Solution

  • Use .values_list() methods to get only the IDs as tuples:

    topping_ids = pizza.toppings.all().values_list("id")
# Example of result ( (4), (5), (12), (54) )