Abstract Doctrine association mapping without discriminator (legacy DB) - php

Question

I'm working with a legacy database (that means no schema changes!) and I need to create a associations between the the Doctrine entities involved. I'll describe the data structure first and then explain what I've tried.
The database has a user table with various other tables also storing user related info. Eg:
siteUser has:
contentId (PK)
firstName
lastName
username
password
...
and siteUser entities have metadata in this system which is along the lines of:
metadataId (PK)
title
description
keywords
createDate
publishDate
contentId
contentTable (discriminator)
...
Almost everything in the database can have Metadata by storing it's PK in the metadata.contentId field and the table name in the metadata.contentTable field. Note that metadata.contentId is not a foreign key, these must have been alien to the DBA as I'm yet to see a single one.
Users on the system can save information they find relevant to them so that they can come back to the system later and don't have to go hunting for the same information again.
This is done with content types called conLink, conVideo, conLeaflet stored as database entities (which have metadata).
For example a conVideo looks like this:
contentId (PK)
embedCode
The way users can store mark this information as being relevant to them is by the system storing it in a link table called userSavedContent:
userSavedContentId (PK)
userId
metadataId
Note that userSavedContent.userId and userSavedContent.metadataId are also not foreign key constraints.
THE APPROACH!
I need to get user's saved content. In SQL this is no problem!
SELECT
metadata.title,
conVideo.embedCode
FROM
userSavedContent
INNER JOIN
metadata ON userSavedContent.metadataId = metadata.metadataId
INNER JOIN
conVideo ON conVideo.contentId = metadata.contentId
WHERE userSavedContent.userId = 193745
AND metadata.contentTable = 'conVideo'
However doing this in Doctrine is more complicated because the value of metadata.contentTable could potentially be any of the conLink, conVideo, conLeaflet entities.
So my application is built using Symfony2 (and Doctrine) and I have models defined for all of the above entities.
In this Metadata is an abstract class with a discriminator on metadata.contentTable:
/**
*
* #ORM\Table(name="metadata")
* #ORM\Entity()
* #ORM\HasLifecycleCallbacks
* #ORM\InheritanceType("SINGLE_TABLE")
* #ORM\DiscriminatorColumn(name="contentTable", type="string")
* #ORM\DiscriminatorMap(
* {
* "conLink" = "MyApp\Bundle\DataApiBundle\Entity\Metadata\ConLinkMetadata",
* "conVideo" = "MyApp\Bundle\DataApiBundle\Entity\Metadata\ConVideoMetadata",
* "siteUser" = "MyApp\Bundle\DataApiBundle\Entity\Metadata\SiteUserMetadata"
* }
* )
*/
abstract class Metadata
The ConVideoMetadata class extends Metadata and adds a content property that associates the ConVideo entity to it:
/**
* #var ContentType $content
*
* #ORM\OneToOne(
* targetEntity="MyApp\Bundle\DataApiBundle\Entity\ContentType\ConVideo",
* inversedBy="metadata",
* cascade={"persist", "remove"}
* )
* #ORM\JoinColumn(name="contentId", referencedColumnName="contentId")
*/
protected $content;
Now the userSavedContent entity has metadata property to associated it to an item of metadata.
/**
* #var Metadata $metadata
*
* #ORM\ManyToOne(
* targetEntity="MyApp\Bundle\DataApiBundle\Entity\Metadata",
* inversedBy="userSavedContent"
* )
* #ORM\JoinColumn(name="id", referencedColumnName="metadataId")
*/
protected $metadata;
And finally the siteUser is related to userSavedContent by the following property on it's entity:
/**
* #ORM\OneToMany(
* targetEntity="MyApp\Bundle\DataApiBundle\Entity\UserSavedContent",
* mappedBy="siteUser",
* cascade={"persist", "remove"},
* orphanRemoval=true
* )
* #ORM\JoinColumn(name="contentId", referencedColumnName="userId")
*/
private $userSavedContentItems;
THE PROBLEM!
In my siteUserRepository class I now need to query for a siteUser and all it's saved content items:
$builder = $this->createQueryBuilder('s')
->select('s', 'm', 'usc', 'uscm', 'uscc')
->innerJoin('s.metadata', 'm')
->leftJoin('s.userSavedContentItems', 'usc')
->leftJoin('usc.metadata', 'uscm')
->leftJoin('uscm.content', 'uscc');
return $builder;
This doesn't work!
"[Semantical Error] Error: Class MyApp\Bundle\DataApiBundle\Entity\Metadata has no association named content"
This makes sense of course since MyApp\Bundle\DataApiBundle\Entity\Metadata doesn't have the content property, it's child MyApp\Bundle\DataApiBundle\Entity\Metadata\ConVideoMetadata is the one with that association. I thought Doctrine would have been able to work this out but apparently not.
So my question is:
Is this approach very wrong? And if not what can I do to make that association/query work?

Answer 1

The fix for this issue was to get Doctrine to eagerly fetch the concrete metadata->content entities. I could declare these explicitly but used Doctrine's MetadataFactory to get the Metadata entity's discriminator for the list of all possible content types.
$metadataFactory = $this->getEntityManager()->getMetadataFactory();
$metadataMetadata = $metadataFactory->getMetadataFor('MyApp\Bundle\DataApiBundle\Entity\Metadata');
foreach ($metadataMetadata->discriminatorMap as $contentEntity) {
$builder->getQuery()
->setFetchMode(
$contentEntity,
'content',
ClassMetadata::FETCH_EAGER
);
}