Doctrine: one to many relationship and cascade persistance - doctrine-orm

Question

I mean I have these two classes (one to many relationship). As you can appreciate in both I have included cascade={"persist"}.
namespace Project\FrontendBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
* #ORM\Entity
* #ORM\Table(name="task")
*/
class Task
{
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
*/
protected $id;
/**
* #ORM\Column(type="string", length=255, name="description", nullable=true)
*/
protected $description;
/**
* #ORM\OneToMany(targetEntity="Tag", mappedBy="task", cascade={"persist"})
**/
protected $tags;
/*************************************/
public function __toString()
{
return $this->description;
}
/**
* Constructor
*/
public function __construct()
{
$this->tags = new \Doctrine\Common\Collections\ArrayCollection();
}
/**
* Get id
*
* #return integer
*/
public function getId()
{
return $this->id;
}
/**
* Set description
*
* #param string $description
* #return Task
*/
public function setDescription($description)
{
$this->description = $description;
return $this;
}
/**
* Get description
*
* #return string
*/
public function getDescription()
{
return $this->description;
}
/**
* Add tags
*
* #param \Project\FrontendBundle\Entity\Tag $tags
* #return Task
*/
public function addTag(\Project\FrontendBundle\Entity\Tag $tags)
{
$this->tags[] = $tags;
return $this;
}
/**
* Remove tags
*
* #param \Project\FrontendBundle\Entity\Tag $tags
*/
public function removeTag(\Project\FrontendBundle\Entity\Tag $tags)
{
$this->tags->removeElement($tags);
}
/**
* Get tags
*
* #return \Doctrine\Common\Collections\Collection
*/
public function getTags()
{
return $this->tags;
}
}
namespace Project\FrontendBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
* #ORM\Entity
* #ORM\Table(name="tag")
*/
class Tag
{
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
*/
protected $id;
/**
* #ORM\Column(type="string", length=255, name="name", nullable=true)
*/
protected $name;
/**
* #ORM\ManyToOne(targetEntity="Task", inversedBy="tags", cascade={"persist"})
* #ORM\JoinColumn(name="task_id", referencedColumnName="id")
**/
private $task;
/**
* Get id
*
* #return integer
*/
public function getId()
{
return $this->id;
}
/**
* Set name
*
* #param string $name
* #return Tag
*/
public function setName($name)
{
$this->name = $name;
return $this;
}
/**
* Get name
*
* #return string
*/
public function getName()
{
return $this->name;
}
/**
* Set task
*
* #param \Project\FrontendBundle\Entity\Task $task
* #return Tag
*/
public function setTask(\Project\FrontendBundle\Entity\Task $task = null)
{
$this->task = $task;
return $this;
}
/**
* Get task
*
* #return \Project\FrontendBundle\Entity\Task
*/
public function getTask()
{
return $this->task;
}
}
In my controller I have this:
$task = new Task();
$tag = new Tag();
$task->addTag($tag);
$em = $this->getDoctrine()->getManager();
$em->persist($item);
$em->flush();
but the foreign key is always NULL, why?

Answer 1

I think in the Task class, the addTag and removeTag should look like this:
public function addTag($tag)
{
$tag->setTask($this);
$this->tags->add($tag);
}
public function removeTag($tag)
{
$tag->setTask(null);
$this->tags->removeElement($tag);
}
Or if you want to add and remove many tags in one function call use these:
public function addTags(Collection $tags)
{
foreach ($tags as $tag) {
$tag->setTask($this);
$this->tags->add($tag);
}
}
public function removeTags(Collection $tags)
{
foreach ($tags as $tag) {
$tag->setTask(null);
$this->tags->removeElement($tag);
}
}