Symfony 2: ManyToMany Relation and Unique Objects - symfony

Question

I'm learning SF2 - really impressed with the job done, faced my first real issue I can't solve myself.
I have two entities: Post and Tag. Shortened code below:
class Tag
{
/**
* #ORM\ManyToMany(targetEntity="Post", mappedBy="tags", cascade={"persist"})
*/
private $posts;
public function __construct()
{
$this->posts = new \Doctrine\Common\Collections\ArrayCollection();
}
/**
* #param \My\AppBundle\Entity\Snippet $posts
* #return Tag
*/
public function addSnippet(\My\AppBundle\Entity\Post $posts)
{
$this->posts[] = $posts;
return $this;
}
/**
* #param \My\AppBundle\Entity\Snippet $snippets
*/
public function removeSnippet(\My\AppBundle\Entity\Post $posts)
{
$this->posts->removeElement($posts);
}
/**
* #return \Doctrine\Common\Collections\Collection
*/
public function getSnippets()
{
return $this->posts;
}
}
class Post
{
/**
* #ORM\ManyToMany(targetEntity="Tag", inversedBy="posts", cascade={"persist"})
* #ORM\JoinTable(name="posts_tags",
* joinColumns={#ORM\JoinColumn(name="post_id", referencedColumnName="id", unique=true, onDelete="cascade")},
* inverseJoinColumns={#ORM\JoinColumn(name="tag_id", referencedColumnName="id", unique=true, onDelete="cascade")}
* )
*/
private $tags;
public function __construct()
{
$this->tags = new \Doctrine\Common\Collections\ArrayCollection();
}
/**
* #param \My\AppBundle\Entity\Tag $tags
* #return Snippet
*/
public function addTag(\My\AppBundle\Entity\Tag $tags)
{
$this->tags[] = $tags;
return $this;
}
/**
* #param \My\AppBundle\Entity\Tag $tags
*/
public function removeTag(\My\AppBundle\Entity\Tag $tags)
{
$this->tags->removeElement($tags);
}
/**
* #return \Doctrine\Common\Collections\Collection
*/
public function getTags()
{
return $this->tags;
}
}
As you can see I have M:M relation between two entities.
I have also a form to add Post with embedded Tag collection:
$builder
->add('title')
->add('tags', 'collection', array(
'type' => new \My\AppBundle\Form\TagType(),
'allow_add' => true,
'by_reference' => false,
'prototype' => true
))
;
TagType form class:
$builder->add('name');
Everything works as expected. Except one thing: if there's a Tag object with the following name, I'm getting SQLSTATE[23000]: Integrity constraint violation MySQL error which is obvious. If I apply unique validation constraint I can add a tag to post (if it already exists in database).
It's obvious I need to check if following tag does exist in database and add it only if does not, but... how to do it Symfony way?
Any suggestions appreciated!

Answer 1

You can use UniqueEntity to handle this. I can't see your annotations on your tags class, or your declaration of 'name' but if you add something like the below it should give you a unique validation constraint based on name with an optional message to throw back.
/**
* #ORM\Entity
* #UniqueEntity(fields="name", message="This tag name already exists")
*/
class Tag...
/**
* #var string $name
*
* #ORM\Column(name="name", type="string", length=255, unique=true)
*/
protected $name;