Getting the values of one-to-many relationships in the parent entity? - doctrine-orm

Question

So I have a Doctrine 2 ORM entity, Trust, with several one-to-many relationships. I can't work out how to populate the arrays for these.
class Trust implements \JsonSerializable {
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #ORM\Column(type="string", nullable=true)
*/
private $name;
/**
* #ORM\OneToMany(targetEntity="TrustPurpose", mappedBy="trust")
*/
private $purpose;
public function __construct() {
}
public function jsonSerialize() {
return [
'id' => $this->id,
'name' => $this->name,
[...]
'purpose' => $this->purpose,
[...]
];
}
}
In my controller, I might use something like the following.
return new JsonResponse($this->entityManager->find(Trust::class, 1));
And get the following output
{
"id" : 1,
"name" : "Some Trust",
"purpose" : {
}
}
I'm struggling to find documentation on how to edit entity Trust to automatically populate my purpose records?
TrustPurpose
class TrustPurpose implements \JsonSerializable {
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #ORM\Column(type="string", nullable=false)
*/
private $purpose;
/**
* #ORM\ManyToOne(targetEntity="Trust", inversedBy="purpose")
* #ORM\JoinColumn(name="trust_id", referencedColumnName="id")
*/
private $trust;
public function __construct() {
}
public function jsonSerialize() {
return [
'id' => $this->id,
'purpose' => $this->purpose,
'trust' => $this->trust,
];
}
}