Symfony 4 #UniqueEntity does not work on GEDMO tree composite fields - php

Question

I seem to have done the set up correctly, but still this does not work, ie, it will not set the database table correctly. In fact it ignores completely the #UniqueEntity annotation.
I am setting up a GEDMO tree, where the title of the category should not be repeated for the same parent_id.
So, looking at the the #UniqueEntity documentation and also at some prior code I built, this should work:
/App/Entity/Category
namespace App\Entity;
use Doctrine\Common\Collections\Collection;
use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;
use Gedmo\Mapping\Annotation as Gedmo;
use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\Validator\Context\ExecutionContextInterface;
use Symfony\Component\Validator\Mapping\ClassMetadata;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
/**
* #Gedmo\Tree(type="nested")
* #ORM\Entity(repositoryClass="App\Repository\CategoryRepository")
* #UniqueEntity(
* fields={"parent", "title"}, // or fields={"parent_id", "title"}
* errorPath="title",
* message="This title is already in use for this parent.")
* #ORM\Table(name="categories")
*/
class Category
{
/**
* #ORM\Column(type="integer")
* #ORM\Id
* #ORM\GeneratedValue
*/
private $id;
/**
* #ORM\Column(type="string", length=190)
*/
private $title;
.....
/**
* #Gedmo\TreeParent
* #ORM\ManyToOne(targetEntity="Category", inversedBy="children")
* #ORM\JoinColumn(referencedColumnName="id", onDelete="CASCADE")
*/
private $parent;
....
}
There's actually a similar question in here, without a solution.

Answer 1

If you want checking on the database level you will need to use Doctrine's UniqueConstraint annotation:
/*
* #ORM\Table(name="categories", uniqueConstraints={
* #ORM\UniqueConstraint(name="uq_cat_parent_title", columns={"parent_id", "title"})
* })
*/
EDIT: Modified my answer to include the name of the index. Doctrine documentation states that it is required.