In Django, what is a one-to-one relationship?

Question

I've always been using ForeignKeys.

Answer 1

A one-to-one relationship is a unique relation between two entities in both directions. I.e. for an entity A there exists only one entity B and vice versa.

The documentation says:

Conceptually, this is similar to a ForeignKey with unique=True, but the "reverse" side of the relation will directly return a single object.

This is most useful as the primary key of a model which "extends" another model in some way; Multi-table inheritance is implemented by adding an implicit one-to-one relation from the child model to the parent model, for example.