MongoDBModel.php

<?php

/**
 * @mongodb:Document
 */
class Band
{
    /**
     * @mongodb:Field(type="string")
     * @var string
     */
    protected $name;
}

/**
 * @mongodb:Document
 */
class Artist
{
    /**
     * @mongodb:Field(type="string")
     * @var string
     */
    protected $name;
}

/**
 * @mongodb:Document
 */
class Performer
{
    /**
     * @mongodb:ReferenceOne(targetDocument="Artist")
     * @var Artist
     */
    protected $artist;

    /**
     * @mongodb:ReferenceOne(targetDocument="Band")
     * @var Band
     */
    protected $band;

    /**
     * @mongodb:EmbedOne(targetDocument="Image") 
     * @var Image
     */
    protected $photo;

    /**
     * @mongodb:Field(type="string")
     * @var string
     */
    protected $instrument;
}

/**
 * @mongodb:EmbeddedDocument
 */
class Image
{
    /**
     * Relative path like "artist/alainsouchon.bmp" 
     * 
     * mongodb:Field(type="string")
     * @var string
     */
    protected $path;
}