What is the key difference between `OneToOneField()` and `ForeignKey()` with `unique=True` in Django?

OneToOneField() vs ForeignKey() in Django

OneToOneField() and ForeignKey() are two Django model fields used to establish relationships between models. While both fields can create a one-to-one relationship, there are subtle differences in their behavior:

OneToOneField()

• Conceptual Similarity: Similar to ForeignKey with unique=True.
• "Reverse" Relation: Directly returns a single object on the other side of the relationship.

ForeignKey() with unique=True

• Conceptual Difference: Specifies a one-to-one relationship by setting unique=True.
• "Reverse" Relation: Returns a QuerySet on the other side of the relationship.

Example

Consider the following models:

In the Python shell:

The OneToOneField's "reverse" relation (engine.car) returns a single object (the Car instance), while the ForeignKey with unique=True's "reverse" relation (engine2.car2_set.all()) returns a QuerySet (a list of all Car2 instances related to that Engine2 instance).

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