Symfony: Handling file entity - symfony

Question

What is the best way to handle a File entity where you have multiple ManyToOne relationships.
Let's say I have 5 entities that has a OneToMany relationship with the File entity.
File.php
/**
* #ORM\ManyToOne(targetEntity="Entity1", inversedBy="files")
* #ORM\JoinColumn(name="entity1_id", referencedColumnName="id", nullable=true, onDelete="CASCADE")
*/
private $entity1;
/**
* #ORM\ManyToOne(targetEntity="Entity2", inversedBy="files")
* #ORM\JoinColumn(name="entity2_id", referencedColumnName="id", nullable=true, onDelete="CASCADE")
*/
private $entity2;
and so one....
Entity1.php
/**
* #ORM\OneToMany(targetEntity="File", mappedBy="entity1" , cascade={"persist", "remove"}, orphanRemoval=true)
*/
protected $images;
The great thing about the above is the getter and setter are set, I can persist and save to the database automatically. The relationship is set and I can load the files by just calling $entity1->getFiles().
What I don't like is every time I want to add another entity that has a OneToMany with File it creates a new column in the database so potential I could have 10 columns referencing Ids from other entities.
What I would like to achieve is saving the class of the entity in the class field and saving the id of the record in an id field but also somehow still allowing the persist and collection saving to work.
entity_id | class
------------------------------------------
2 | ProjectBundle/Entity/Entity1
3 | ProjectBundle/Entity/Entity2

Answer 1

You don't need the class field at all.
Use Doctrine's inheritance mapping by creating a base class for all entities you want to refer from File:
/**
* #ORM\Entity()
* #ORM\InheritanceType("SINGLE_TABLE")
* #ORM\DiscriminatorColumn(name="entityType", type="string")
* #ORM\DiscriminatorMap({
* "entity1" = "Entity1",
* "entity2" = "Entity2"
* })
*/
abstract class BaseEntity
{
/**
* #ORM\ManyToMany(targetEntity="File", mappedBy="entities" , cascade={"persist", "remove"}, orphanRemoval=true)
*/
protected $images;
}
/**
* #ORM\Entity
*/
class Entity1 extends BaseEntity
{
...
}
/**
* #ORM\Entity
*/
class Entity2 extends BaseEntity
{
...
}
This way you can refer to both Entity1 and Entity2 by their base class from File. When calling getEntities, Doctrine creates instances of the proper class "automatically", based on the discriminator value of each entity.
File
/**
* #ORM\ManyToMany(targetEntity="Entity", inversedBy="images")
* #ORM\JoinColumn(name="entity_id", referencedColumnName="id", nullable=true, onDelete="CASCADE")
*/
protected $entities;
OneToMany, ManyToOne become ManyToMany because now the file may have many entities.