Repository from entity in symfony?

I have this code, from an entity:

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;
use JMS\Serializer\Annotation\Type;
use JMS\Serializer\Annotation\Exclude;
use JMS\Serializer\Annotation\Accessor;
use AppBundle\Validator\Constraints as ImplikaAssert;
use Symfony\Component\PropertyInfo\PropertyInfoExtractor;
use Symfony\Component\PropertyInfo\Extractor\PhpDocExtractor;
use Symfony\Component\PropertyInfo\Extractor\ReflectionExtractor;
use AppBundle\Entity\Provincia as Provincia;
use AppBundle\Repository\ProvinciaRepository;
/**
 * Alumno
 *
 * @ORM\Table(name="alumno")
 * @ORM\Entity(repositoryClass="AppBundle\Repository\AlumnoRepository")
 * 
 */
class Alumno
{
    /**
     * @var int
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     * @Type("integer")
     */
    private $id;

    /**
     * @var string
     *
     * @ORM\Column(name="nombre", type="string", length=100)
     * @Type("string")     
     */
    private $nombre;

    /**
     * @var string
     *
     * @ORM\Column(name="apellido_1", type="string", length=100)
     * @Type("string")     
     */
    private $apellido1;

    /**
     * @var string
     *
     * @ORM\Column(name="apellido_2", type="string", length=100, nullable=true)
     * @Type("string")     
     */
    private $apellido2;

    /**
     * @var string
     * @ImplikaAssert\IsValidIdNumber
     * 
     * @ORM\Column(name="dni", type="documento_identidad", length=20)
     * @Type("string")
     */
    private $dni;

    /**
     * @var \DateTime
     *
     * @ORM\Column(name="fecha_nacimiento", type="date")
     * @Type("DateTime<'Y-m-d'>")
     */
    private $fecha_nacimiento;

    /**
     * @var string
     *
     * @ORM\Column(name="email", type="string", length=100)
     * @Type("string")     
     */
    private $email;

    /**
     * @ORM\ManyToOne(targetEntity="Provincia")
     * @ORM\JoinColumn(name="provincia_id", referencedColumnName="id", onDelete="SET NULL")
     * @Type("string")
     * @Accessor(getter="getProvinciaNombre",setter="setProvinciaNombre")     
     */
    private $provincia;


    public function __toString() 
    {
        return $this->apellido1 . ' ' .
               $this->apellido2 . ', ' . 
               $this->nombre . ' - ' . 
               $this->dni;
    } 

    /**
     * Constructor
     */
    public function __construct()
    {
        $this->matriculas = new ArrayCollection();
    }

    /**
     * Get id
     *
     * @return int
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Set nombre
     *
     * @param string $nombre
     *
     * @return Alumno
     */
    public function setNombre($nombre)
    {
        $this->nombre = $nombre;

        return $this;
    }

    /**
     * Get nombre
     *
     * @return string
     */
    public function getNombre()
    {
        return $this->nombre;
    }

    /**
     * Set apellido1
     *
     * @param string $apellido1
     *
     * @return Alumno
     */
    public function setApellido1($apellido1)
    {
        $this->apellido1 = $apellido1;

        return $this;
    }

    /**
     * Get apellido1
     *
     * @return string
     */
    public function getApellido1()
    {
        return $this->apellido1;
    }

    /**
     * Set apellido2
     *
     * @param string $apellido2
     *
     * @return Alumno
     */
    public function setApellido2($apellido2)
    {
        $this->apellido2 = $apellido2;

        return $this;
    }

    /**
     * Get apellido2
     *
     * @return string
     */
    public function getApellido2()
    {
        return $this->apellido2;
    }

    /**
     * Set email
     *
     * @param string $email
     *
     * @return Alumno
     */
    public function setEmail($email)
    {
        $this->email = $email;

        return $this;
    }

    /**
     * Get email
     *
     * @return string
     */
    public function getEmail()
    {
        return $this->email;
    }

    /**
     * Set provincia
     *
     * @param string $provincia
     *
     * @return Alumno
     */
    public function setProvincia($provincia)
    {
        $this->provincia = $provincia;

        return $this;
    }

    /**
     * Get provincia
     *
     * @return string
     */
    public function getProvincia()
    {
        return $this->provincia;
    }

    public function getProvinciaNombre()
    {
        $provincia = new Provincia();
        $provincia = $this->provincia;
        return $provincia->getNombre();
    }

    public function setProvinciaNombre($nombre)
    {
        $this->provincia = ProvinciaRepository->getByNombre($nombre);
    }        
}

As you can see I have a property that deserializar uses the annotation @Accessor. What I would like is for the object when it deserializes in the province to insert a province object that I already have in the database.

My first idea was to create a custom repository and try to call it.

My second idea has been to generate a service to call the repository, but it has not solved either.

Any other ideas ??