Django OneToOneField - One-to-one relationships

A OneToOneField is used when you want to create a One-to-one relations. In this article, we will go over the usecase for such a field and how it should be implemented.

When to use a one-to-one relationship?

You generally won't use one-to-one relationships that often and I also won't really advise them, except for very specific cases, like this one:

Say you have a user model. In that model you also store details about their profile (bio, address, profile picture etc). When that table gets very big, a lot of columns could influence the speed of retrieving items from that table. In that case, it might be a good idea to split the user details from the profile details and create a separated table from that. Connecting the two through a OneToOneField would make sense here, since generally a user won't have two profiles or vice versa.

OneToOneField example

Let's take the previous example and turn that into some code. It would look like this:

class User(AbstractBaseUser):
    profile = OneToOneField(Profile, on_delete=models.CASCADE)
    # other fields you want to add beside the default ones from AbstractBaseUser

class Profile(models.Model):
    bio = TextField()
    # more profile fields

You can then get the bio from the user by doing this:

u = User.objects.get(id=1)
print(u.profile.bio)

Another advantage of this approach is that you can generally cache the Profile table for a longer time. But, again, I generally wouldn't recommend this approach as it makes things a lot more complicated.

Written by Stan Triepels

Stan is professional web developer working mainly with Django and VueJS. With years of experience under the belt, he is comfortable writing about his past mistakes and ongoing learnings.