ODM: Cannot achieve bi-directional relationship - doctrine

Question

I have two documents. I am trying to find all papers that are associated to a specific person. The documents are saving in their collections, and a reference is being created from Person to Paper, but not the other way around.
/** #ODM\Document */
class Paper
{
/**
* #ODM\Id
*/
protected $id;
/** #ODM\ReferenceOne(targetDocument="Person", cascade={"all"}, mappedBy="papers") */
protected $person;
public function __get($property) {
return $this->$property;
}
public function __set($property, $value) {
$this->$property = $value;
}
public function toArray() {
return get_object_vars($this);
}
}
/** #ODM\Document */
class Person
{
/**
* #ODM\Id
*/
protected $id;
/** #ODM\ReferenceMany(targetDocument="Paper", cascade={"all"}, inversedBy="person") */
protected $papers;
public function __get($property) {
return $this->$property;
}
public function __set($property, $value) {
$this->$property = $value;
}
public function toArray() {
return get_object_vars($this);
}
}
CREATE A NEW BI-DIRECTIONAL REFERENCE
$person = $dm->getRespository('Person')->find($person_id);
$paper = new Paper();
$person->papers->add($paper);
$dm->persist($person);
$dm->flush();
Later in the code, this query returns 0 results; shouldn't it be returning papers written by specified person?
$papers = $dm->createQueryBuilder('Paper')
->field('person.$id')->equals(new \MongoId($person_id_as_string))
->getQuery()->execute();

Answer 1

If Paper::person is annotated with "mappedBy" it means that Paper is not the "owning side" and doctrine will not persist any changes to Paper::person.
To make your query work, make Paper the owning side so Paper stores the reference to Person.
/** #ODM\Document */
class Person
{
/** #ODM\ReferenceMany(targetDocument="Paper", mappedBy="person") */
protected $papers;
}
/** #ODM\Document */
class Paper
{
/** #ODM\ReferenceOne(targetDocument="Person", inversedBy="papers") */
protected $person;
}
Creating a paper and persisting a reference to person:
$person = $dm->getRespository('Person')->find($person_id);
$paper = new Paper();
$paper->person = $person;
$dm->persist($paper);
$dm->flush();
Querying Papers by $person:
$papers = $dm->createQueryBuilder('Paper')
->field('person')->references($person)
->getQuery()->execute();