Query on Doctrine class table inheritance with required fields - symfony

Question

My domain has a parent IncidenceMessage class and several child classes (i.e. IncidenceMessageText).
I have the following class table inheritance configuration:
Domain\Model\IncidenceMessage\IncidenceMessage:
type: entity
repositoryClass: Infrastructure\Domain\Model\IncidenceMessage\DoctrineIncidenceMessageRepository
table: incidence_messages
inheritanceType: JOINED
discriminatorColumn:
name: type
type: string
length: 30
discriminatorMap:
text: IncidenceMessageText
image: IncidenceMessageImage
audio: IncidenceMessageAudio
video: IncidenceMessageVideo
fields:
...
I can create any IncidenceMessage entity correctly.
Having only a IncidenceMessageText in database, when I try to fetch incidence messages I get the following error:
TypeError: Argument 1 passed to Domain\Model\File\FileId::__construct() must be of the type string, null given
(FileId is a value object that represents the id of a File entity)
IncidenceMessageImage has a File field that is a foreign key and it is required.
It makes no sense to me that Doctrine fetches File when IncidenceMessageText doesn't have that field.
While debugging, I discovered that doctrine does a SELECT with LEFT JOINs with every single IncidenceMessage table and this calls my FileTypeId::convertToPHPValue method:
class FileIdType extends Type
{
public function convertToDatabaseValue($value, AbstractPlatform $platform)
{
return new FileId($value);
}
}
AFAIK, the problem here is that child classes have required fields but that shouldn't be a stopper, right?

Answer 1

I found a possible workaround. On my custom DBAL Type FileIdType, I checked if the value was null before instantiating FileId:
use Doctrine\DBAL\Types\Type;
class FileIdType extends Type
{
public function convertToPHPValue($value, AbstractPlatform $platform)
{
return $value ? new FileId($value) : null;
}
}