Question

I have the following code:

class Album(models.Model):
  name = models.CharField(max_length=255, unique=True, null=False)
  rating = models.ForeignKey("Rating", null=False)

class Rating(models.Model):
  value = models.IntegerField(null=False, default=0)

What is the best way (in the django/python philosophy) to create an object (Album) and it’s sub object (Rating) and save it?

I have done this:

a = Album()
a.name = "..."
r = Rating()
r.save()
a.rating = r
a.save()

I don’t like this because the part of creating the sub object empty is totally not useful.
I’d prefer some simple way like this – the sub-object should be created automatically:

a = Album()
a.name = "..."
a.save()

Answer 1

You’ll want to look into signals.

Essentially a signals are sent when an Object is saved.

Using a pre_save signal you can then create a Rating and associate it to the new Album jsut before it is saved for the first time.

from django.db.models.signals import pre_save
from django.dispatch import receiver
from myapp.models import Album, Rating

@receiver(pre_save, sender=Album)
def add_rating_to_album(sender, **kwargs):

    # If saving a new Album
    if not instance.id:

        # Create and save a new rating
        rating = Rating()
        rating.save()

        # Associate it to the Album being saved
        instance.rating = rating

    # Continue to normal save with new rating applied

I haven’t tested this specific code but it should get you in the right direction