Delete an entity with two OneToOne relations - symfony

Question

I have a probleme for a job in Symfony 4.2.
I'm a beginner on Symfony and I need help for understand cascade deletion, and what I have a foreign key error
I have 3 entity like this :
The first is call Image
class Image
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\Column(type="string", length=255)
*/
private $name;
/**
* #ORM\OneToOne(
* targetEntity="App\Entity\Thumbnail",
* mappedBy="Image",
* cascade={"persist"},
* orphanRemoval=true
* )
*/
private $Thumbnail;
}
the second is the Thumbnail of this image :
class Thumbnail
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\Column(type="string", length=255)
*/
private $name;
/**
* #ORM\OneToOne(
* targetEntity="App\Entity\Image",
* inversedBy="Thumbnail",
* cascade={"persist", "remove"}
* )
* #ORM\JoinColumn(nullable=false)
*/
private $image;
}
and a Div which contain a Thumbnail :
class Div
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\Column(type="string", length=255)
*/
private $name;
/**
* #ORM\OneToOne(targetEntity="App\Entity\Thumbnail", cascade={"persist", "remove"})
*/
private $Thumbnail;
}
this is my three entities, and my problem is when I try to delete one of this three entities because :
When I delete an Image I need to delete his Thumbnail, but the Div can live without Thumbnail so I mustn't delete the Div.
When I delete a Thumbnail, I mustn't delete the Image, and I mustn't delete the Div
When I delete the Div I mustn't delete the Thumbnail.
I would like to know the best practice for do this job.
Thank for help and sorry for my bad english.

Answer 1

Try below code in your Div entity:
/**
* #ORM\OneToOne(targetEntity="App\Entity\Thumbnail", cascade={"persist", "remove"})
* #ORM\JoinColumn(name="thumbnail_id", referencedColumnName="id", onDelete="SET NULL")
*/
private $Thumbnail;