How to know if an object from a relation exists in the database

I'm using Symfony with Doctrine.

I have two classes defined, Person and Student, a relation one to one.

Each Student is related to a Person, but not every Person has a relation with a Student.

When I call ...

$person->getStudent();

... I always get and object, regardless some Person's doesn't have a Student. How can I know it doesn't (the Student) exist in the database?

Thanks.

Solution

I think

$person->getStudent()->exists();

should do it. At least according to the Doctrine API documentation.
The object you get is probably some kind of Null record.