Doctrine OneToMany Relation based on entityUid field - php

Question

i'me working on a project with alot of the entities have string uid LIKE ENTITY.XXXX.
I'm seaching a way to relate some entities using doctrine annotations.
In particular the entity Media that contains all the links to the media files, to other entities becouse the relations between Media and the other entities like Document, Building etc is based on a field entityUid inside the Media entity, so the field entityUid is promiscuous becouse can contain the uid form different other entities.
I realize that cannot do a reverse mapping becouse i cant populate correctoy the reversed entity becouse is promiscuous, what i'm trying to do is a direct relation between for example Document 1:n Media based on Document.uid 1:n Media.entityUid and Bulding 1:n Media based on Document.uid 1:n Media.entityUid.
I write the entities:
class Media(){
/**
* #var integer
*
* #ORM\Column(name="id", type="integer", nullable=false)
* #ORM\Id
* #ORM\GeneratedValue(strategy="IDENTITY")
*
*/
private $id;
/**
* #var string
* #ORM\Column(name="entityUid", type="string", nullable=false)
*/
private $entityUid;
/**
* #var string
*
* #ORM\Column(name="link", type="string", nullable=true)
*/
private $link;
... other stuff.
}
class Document(){
/**
* #var integer
*
* #ORM\Column(name="id", type="integer", nullable=false)
* #ORM\Id
* #ORM\GeneratedValue(strategy="IDENTITY")
*
*/
private $id;
/**
*#var Media[]
*
*/
private $medias;
/**
* #var string
* #ORM\Column(name="uid", type="string", nullable=false)
*/
protected $uid;
... other stuff
}
class Building(){
/**
* #var integer
*
* #ORM\Column(name="id", type="integer", nullable=false)
* #ORM\Id
* #ORM\GeneratedValue(strategy="IDENTITY")
*
*/
private $id;
/**
*#var Media[]
*
*/
private $medias;
/**
* #var string
* #ORM\Column(name="uid", type="string", nullable=false)
*/
protected $uid;
... other stuff
}
The problem is on the definition on the relation OneToMany, based not form the id fiels but uid fileds.
I was not able to find a correct annotation to create an unidirection OneToMany relation without creating a support table like a ManyToMany document_media , building_media, that would make useless the entities uids.
Tx for your time.