gistfile1.php

<?php

namespace AppBundle\Form\DataTransformer;

use Symfony\Component\Form\DataTransformerInterface;
use Symfony\Component\Form\Exception\TransformationFailedException;
use AppBundle\Manager\CategoryManager;
use AppBundle\Entity\Category;

class CategoryToStringTransformer implements DataTransformerInterface
{
    private $categoryManager;

    public function __construct(CategoryManager $categoryManager)
    {
        $this->categoryManager = $categoryManager;
    }

    /**
     * Transforms a Category to a string.
     *
     * @param  Category|null $user
     * @return string
     */
    public function transform(Category $category = null)
    {
        if (null === $category) {
            return "";
        }

        return $category->getName();
    }

    /**
     * Transforms a string to a Category.
     *
     * @param  string $email
     * @return Category|null
     * @throws TransformationFailedException if User is not found.
     */
    public function reverseTransform($name)
    {
        if (!$name) {
            return null;
        }

        $cateogry = $this->categoryManager->findOneByName($name);

        if (null === $category) {
            $category = new Category();
            $category->setName($name)
        }

        return $category;
    }
}