Doctrine ODM Unique constraint not validating property - php

Question

I can't figure out why Doctrine's ODM Unique constraint isn't working for me.
Below is a Page Class with the property "title", that needs to be unique amongst all Pages.
namespace App\Document;
use Symfony\Component\Validator\Constraints as Assert;
use Doctrine\Bundle\MongoDBBundle\Validator\Constraints\Unique as MongoDBUnique;
use Doctrine\ODM\MongoDB\Mapping\Annotations as ODM;
use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;
use App\Repository\PageRepository;
use App\Document\Embeded\Section;
/**
* #ODM\Document(repositoryClass=PageRepository::class)
* #MongoDBUnique(fields="title")
*/
class Page
{
/** #ODM\Id() */
private $id;
/** #ODM\ReferenceOne(targetDocument=Site::class) */
private $site;
/** #ODM\Field(type="string")
* #ODM\UniqueIndex(order="asc")
*/
private $title;
// ...
Within the controller, $form->handleRequest($request) is called, followed by the query: if ($form->isSubmitted() && $form->isValid())
The form is always returned as valid. The ODM Unique constraint seems to be ignored. I've also tried to add a custom Validation Constraint and was met with the same issue.
Do I need to add any additional configuration to get this to work?

Answer 1

Symfony forms only validate the top-level object by design. In this case, the Page Class was attached to an embedded form.
Solution: add Symfony's #Valid() constraint to the property, within the top-level object.
/** #ODM\ReferenceOne(targetDocument="App\Document\Page", cascade={"persist"}, orphanRemoval=true)
* #ODM\Index
* #Assert\Valid()
*/
private $page;