Doctrine, ralation ManyToOne - php

Question

When a try update my database I got error:
SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails
(symfony.#sql-d8c_55, CONSTRAINT FK_957A6479A233CB39 FOREIGN KEY
(klient_id) REFERENCES klient (id))
My class user:
namespace AppBundle\Entity;
use Doctrine\Common\Collections\ArrayCollection;
use FOS\UserBundle\Model\User as BaseUser;
use Doctrine\ORM\Mapping as ORM;
/**
* Class User
* #package AppBundle\Entity
*
* #ORM\Table("fos_user")
* #ORM\Entity()
*/
class User extends BaseUser
{
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
*/
protected $id;
/**
* #ORM\ManyToOne(targetEntity="AppBundle\Entity\Klient", inversedBy="users")
* #ORM\JoinColumn(nullable=false)
*/
private $klient;
/**
* #return mixed
*/
public function getKlient()
{
return $this->klient;
}
/**
* #param mixed $klient
*/
public function setKlient($klient)
{
$this->klient = $klient;
}
public function __construct()
{
parent::__construct();
}
}
class Klient
namespace AppBundle\Entity;
use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\ORM\Mapping as ORM;
/**
* Klient
*
* #ORM\Table(name="klient")
* #ORM\Entity(repositoryClass="AppBundle\Repository\KlientRepository")
*/
class Klient
{
/**
* #var int
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var string
*
* #ORM\Column(name="nazwa", type="string", length=255, unique=true)
*/
private $nazwa;
/**
* #ORM\OneToMany(targetEntity="AppBundle\Entity\User", mappedBy="klient")
*/
private $users;
/**
* Get id
*
* #return int
*/
public function getId()
{
return $this->id;
}
/**
* Set nazwa
*
* #param string $nazwa
*
* #return Klient
*/
public function setNazwa($nazwa)
{
$this->nazwa = $nazwa;
return $this;
}
/**
* Get nazwa
*
* #return string
*/
public function getNazwa()
{
return $this->nazwa;
}
public function __construct()
{
$this->users = new ArrayCollection();
}
}

Answer 1

in my opinion you have this error because you already have datas in your database. When you try to add the foreign key on your user table, kcient_id is null. And in your definition, you specify nullable: false.
I suggest you proceed in two times.
Edit your annotation to nullable: true, update your database and link your client to klient
Re-edit your annotation to nullable: false, it should be ok