Doctrine repository for entities implementing a common interface - php

Question

I have a few different doctrine entities implementing a common interface and I want to (ideally) create a repository in doctrine that allows me to query with ordering/pagination across all those entities (a union in plain SQL). The entities don't inherit from a common base class.
Specifically the interface allows an object to be used as a tag:
interface My\TaggableInterface
{
// get object UUID
public function getObjectIdentity(): string
// get the tag text
public function getTagString(): string
}
class My\Entity implements My\TaggableInterface
class My\Other\Entity implements My\TaggableInterface
I was hoping to create a custom repository that managed the union, so I could write:
$entityManager()->getRepository('My\\TaggableInterface')
->findBy(
//criteria
)`
But there doesn't seem to be a way to create a temporary table from an interface or support for union in the doctrine query builder. I want to avoid using native (My)SQL if possible, but I can't see how to achieve this using Doctrine?
Many thanks.

Answer 1

You can't do it with a single query. Even if you could somehow construct this query, doctrine wouldn't know how to hydrate the results.
You can however find and query all entities implementing your interface without having to list them all somewhere in your code:
$result = array();
$criteria = array(
// criteria
);
foreach ($em->getMetadataFactory()->getAllMetadata() as $m) {
$class = $m->getName();
$reflClass = new \ReflectionClass($class);
if ($reflClass->implementsInterface('My\TaggableInterface')) {
$result = array_merge($result, $em->getRepository($class)->findBy($criteria));
}
}
// results of various entity classes are now all in $result

Answer 2

An outline of the solution I used is below. Since I'm hydrating the results from each table into a tag entity (which can be persisted using the ORM if the tag is selected by the user) there's no need to hydrate multiple entity classes from the same result set.
$sql = <<<EOF
SELECT `id`, `text`
FROM tag_table
GROUP BY `text`
UNION
SELECT UUID() as `id`, `some_text_field` as `text`
FROM another_table
GROUP BY `some_text_field`
EOF;
$resultMapping = new ResultSetMapping();
$resultMapping->addEntityResult('My\Tag\Entity', 'tag');
$resultMapping->addFieldResult('tag', 'id', 'id');
$resultMapping->addFieldResult('tag', 'text', 'text');
$nativeQuery = $entityManager->createNativeQuery($sql, $resultMapping);
$result = $nativeQuery->getResult();
The SQL can then be extended to handle pagination, and to make sure the tag entity table is used (instead of a newly generated uuid for the same tag text) when duplicate entries across the tables are removed by the union.