Doctrine ODM: Embedding multiple GridFS documents exception - mongodb

Question

I'm trying to embed a thumbnail image inside of it's main larger image in GridFS via Doctrine / Symfony 2.
The main image document is as follows,
<?php
namespace namespace\goes\here\Document;
use Doctrine\ODM\MongoDB\Mapping\Annotations as MongoDB;
/**
* #MongoDB\Document
*/
class FullSizeImage
{
/** #MongoDB\Id */
private $id;
/** #MongoDB\File */
private $file;
/** #MongoDB\String */
private $filename;
/** #MongoDB\String */
private $mimeType;
/** #MongoDB\Date */
private $uploadDate;
/** #MongoDB\Int */
private $userId;
/** #MongoDB\Int */
private $length;
/** #MongoDB\Int */
private $chunkSize;
/** #MongoDB\String */
private $md5;
/** #MongoDB\Collection */
private $tags = array();
/** #MongoDB\EmbedOne(targetDocument="Thumbnail") */
private $thumbnail;
public function getId()
{
return $this->id;
}
public function setId($id)
{
$this->id = $id;
}
public function getTags()
{
return $this->tags;
}
public function setTags($tags)
{
$this->tags = $tags;
}
public function getFile()
{
return $this->file;
}
public function setFile($file)
{
$this->file = $file;
}
public function getFilename()
{
return $this->filename;
}
public function setFilename($filename)
{
$this->filename = $filename;
}
public function getMimeType()
{
return $this->mimeType;
}
public function setMimeType($mimeType)
{
$this->mimeType = $mimeType;
}
public function getChunkSize()
{
return $this->chunkSize;
}
public function getLength()
{
return $this->length;
}
public function getMd5()
{
return $this->md5;
}
public function getUploadDate()
{
return $this->uploadDate;
}
public function getUserId()
{
return $this->userId;
}
public function setUserId($userId)
{
$this->userId = $userId;
}
public function getThumbnail()
{
return $this->thumbnail;
}
public function setThumbnail($thumbnail)
{
$this->thumbnail = $thumbnail;
}
}
and the thumbnail document, that lives under the same namespace, is as follows,
<?php
namespace namespace\goes\here\Document;
use Doctrine\ODM\MongoDB\Mapping\Annotations as MongoDB;
/** #MongoDB\EmbeddedDocument */
class Thumbnail
{
/** #MongoDB\Id */
private $id;
/** #MongoDB\File */
private $file;
/** #MongoDB\String */
private $filename;
/** #MongoDB\String */
private $mimeType;
/** #MongoDB\Date */
private $uploadDate;
/** #MongoDB\Int */
private $length;
/** #MongoDB\Int */
private $chunkSize;
/** #MongoDB\String */
private $md5;
public function getId()
{
return $this->id;
}
public function setId($id)
{
$this->id = $id;
}
public function getFile()
{
return $this->file;
}
public function setFile($file)
{
$this->file = $file;
}
public function getFilename()
{
return $this->filename;
}
public function setFilename($filename)
{
$this->filename = $filename;
}
public function getMimeType()
{
return $this->mimeType;
}
public function setMimeType($mimeType)
{
$this->mimeType = $mimeType;
}
public function getChunkSize()
{
return $this->chunkSize;
}
public function getLength()
{
return $this->length;
}
public function getMd5()
{
return $this->md5;
}
public function getUploadDate()
{
return $this->uploadDate;
}
}
When I try to persist / flush the FullSizeImage,
$thumbnail = new Thumbnail();
$thumbnail->setFile($thumbPath);
$thumbnail->setFilename($thumbName);
$thumbnail->setMimeType($thumbMimeType);
$thumbnail->setUserId($user->getId());
$fsi = new FullSizeImage();
$fsi->setFile($file->getRealPath());
$fsi->setTags(array('tag', 'tag', 'tag'));
$fsi->setFilename($file->getFilename());
$fsi->setMimeType($file->getMimeType());
$fsi->setUserId($user->getId());
$fsi->setThumbnail($thumbnail);
$dm->persist($fsi);
$dm->flush();
I encounter this exception,
Could not store file: zero-length keys are not allowed, did you use $
with double quotes?
Am I missing something? Or is there a better way to go about storing these images and their relationship in mongo?

Answer 1

Field, which maps GridFS have to be the top-most-level document. It can be referenced by other documents, but it can't be embed by any other document. It's because GridFS implementation in Mongo ODM.
I've had a similiar issue some time ago. I've ended up with solution described above.
More details: https://github.com/doctrine/mongodb-odm/issues/911