Prevent Object recursion/loop by reference in PHP - php

Question

Haven't found an answer yet but I'm sure there must be one: how do I prevent an object recursion/loop when objects reference each other? An example:
class Patient {
private $Issues = array();
[...]
public function __construct($id) {
[ Get data from DB ]
while ($row = $result->fetch_assoc()) {
$this->Issues[$row['idIssue']] = new Issue($row['idIssue']);
}
[...]
}
}
class Issue {
private $Patient;
[...]
public function __construct($id) {
[ Get data from DB ]
$this->Patient = new Patient($row['idPatient']); <-- Leads to recursion as the patient will load all it's Issues() etc. etc.
[...]
}
}
How do I prevent this? I could use the id of the Patient() instead of the real object but that feels like a hack. Is there a way to use the real object?

Answer 1

Do not recreate object. Just pass the instance of the master object to the detail constructor. E.g.:
class Patient {
private $Issues = array();
[...]
public function __construct($id) {
[ Get data from DB ]
while ($row = $result->fetch_assoc()) {
$this->Issues[$row['idIssue']] = new Issue($row['idIssue'], $this);
}
[...]
}
}
class Issue {
private $Patient;
[...]
public function __construct($id, Patient $patient) {
[ Get data from DB ]
$this->Patient = $patient
[...]
}
}

Answer 2

You can (should !) separate the DB connection/queries from the entities definitions and pass references to relations, otherwise, you can't mock entities, plus mixing DB connection and entities definition goes against the separation of concerns :
// somewhere in your code
$idPatient = 42;
$patient = new Patient();
$patient->setId($idPatient);
// get datas from DB
while ($row = $result->fetch_assoc())
{
$issue = new Issue();
$issue->setId($row['idIssue'])
->setPatient($patient);
$patient->addIssue($issue);
// or, shorter way :
// $patient->addIssues((new Issue())->setId($row['idIssue'])
// ->setPatient($patient));
}
class Patient {
private $Issues = array();
private $Id;
public function addIssue(Issue $issue): self
{
$this->Issues[] = $issue;
return $this;
}
public function setId(int $id): self
{
$this->Id = $id;
return $this;
}
}
class Issue {
private $Patient;
private $Id;
public function addPatient(Patient $patient): self
{
$this->Patient = $patient;
return $this;
}
public function setId(int $id): self
{
$this->Id = $id;
return $this;
}
}