class User{
    /**
     * @var ArrayCollection
     *
     * @ORM\OneToMany(targetEntity="Shop\Product\ProductBundle\Entity\Product", mappedBy="author")
     */
    private $categories;


    public function __construct()
    {
        $this->salt = bin2hex(random_bytes(10));
        $this->categories = new ArrayCollection();
    }

    /**
     * @return \Doctrine\Common\Collections\Collection
     */
    public function getCategories()
    {
        return $this->categories;
    }

    /**
     * @param Category $category
     * @return User
     */
    public function addCategories(Category $category)
    {
        $this->categories[] = $category;

        return $this;
    }
}
}

class Product
{
/**
     * @var int
     *
     * @ORM\Column(name="author_id", type="integer")
     */
    private $authorId;

    /**
     * @var string
     *
     * @ORM\ManyToOne(targetEntity="Customers\User\UserBundle\Entity\User", inversedBy="categories")
     * @ORM\JoinColumn(name="author_id", referencedColumnName="id")
     */
    private $author;

    /**
     * @var string
     *
     * @ORM\Column(name="createdOn", type="datetime", length=255)
     */
    private $createdOn;

    function __construct()
    {
        $this->createdOn = new \DateTime('now', new \DateTimeZone('Europe/Sofia'));
    }

    /**
     * @return int
     */
    public function getAuthorId()
    {
        return $this->authorId;
    }

    /**
     * @param int $authorId
     *
     * @return Product
     */
    public function setAuthorId($authorId)
    {
        $this->authorId = $authorId;

        return $this;
    }

    /**
     * Set author
     *
     * @param User $author
     *
     * @return Product
     */
    public function setAuthor(User $author = null)
    {
        $this->author = $author;

        return $this;
    }

    /**
     * Get author
     *
     * @return User
     */
    public function getAuthor()
    {
        return $this->author;
    }
}

//new product controller

$product->setAuthor($this->getUser());