symfony2 - add value to protected object - symfony

Question

How can I set the protected object user? After filling the form i have to add user object with current user data (for example like saving comments). I tried something like that:
if ($form->isValid()) {
$comment = $form->getData();
$comment->user = $this->contextSecurity->getToken()->getUser();
$this->model->save($comment);
}
And i've got this error
FatalErrorException: Error: Cannot access protected property AppBundle\Entity\Comment::$user in /home/AppBundle/Controller/CommentsController.php line 184
Here is my Comment entity:
class Comment
{
/**
* Id.
*
* #ORM\Id
* #ORM\Column(
* type="integer",
* nullable=false,
* options={
* "unsigned" = true
* }
* )
* #ORM\GeneratedValue(strategy="IDENTITY")
*
* #var integer $id
*/
private $id;
/**
* Content.
*
* #ORM\Column(
* name="content",
* type="string",
* length=250,
* nullable=false
* )
* #Assert\NotBlank(groups={"c-default"})
* #Assert\Length(min=3, max=250, groups={"c-default"})
*
* #var string $content
*/
private $content;
/**
* #ORM\ManyToOne(targetEntity="User", inversedBy="comments")
* #ORM\JoinColumn(name="user_id", referencedColumnName="id", nullable=false)
*/
protected $user;
I'm using Symfony2.3. Any help will be appreciated.

Answer 1

You can't modify protected properties from outside of the object. You need a public property or a setter for that.
class Comment
{
// ...
public function setUser(User $user)
{
$this->user = $user;
}
}
And in a controller you can write:
$comment->setUser($this->getUser());

Answer 2

This question is not related to Symfony2, at first you should read about php types, especially about objects. read here and then here
You should understand how Visibility works. After that you will understand that access to protected/private properties of the object is only available from the object itself, so you need to create public method
setUser($user) {
$this->user = $user;
}

Answer 3

I always use protected, If i want edit variable or take the value, I use the getter and setter:
public function setUser($user) {
$this->user = $user;
}
public function getUser(){
return $this->user;
}