Doctrine DQL, class table inheritance and access to subclass fields

You can easily solve this by left-joining your base entity with your inheritance class using the id:

SELECT a FROM Entities\Auction a
    INNER JOIN a.item i 
    INNER JOIN Entities\Book b WITH b.id = i.id 
    INNER JOIN b.bookTypes bt
    WHERE bt.type = 'Fantasy' 
    AND...

or with a queryBuilder:

$queryBuilderb->select('a')
   ->from('Entities\Auction', 'a')
   ->innerJoin('a.item', 'i')
   ->innerJoin('Entities\Book', 'b', 'WITH', 'b.id = i.id')
   ->innerJoin('b.bookTypes', 'bt')
   ->where('bt.type = :type')
   ->andWhere(...
   ->setParameter('type', 'Fantasy');

This is based on the answer given by Ian Philips in the question here

Updated:

I've discovered a solution for this. See my answer for this related question:

Doctrine2: Polymorphic Queries: Searching on properties of subclasses

The Doctrine team has stated that they're not going to add support for this:

https://github.com/doctrine/orm/issues/2237

Pertinent comments from that page:

Thats indeed tricky. That syntax alone can, however, never work, because there might be several subclasses that have a field named "d", so Doctrine would not know which field you mean.

---

I am closing this one.

The requirement of this issue is basically violating OO principles.

If you really need to filter across multiple child-entities in your inheritance, then try something as following instead:

SELECT r FROM Root r WHERE r.id IN ( SELECT c.id FROM Child c WHERE c.field = :value )

As Matt stated, this is an old issue that Doctrine Project won't fix (DDC-16).

The problem is that doctrine's DQL is a statically typed language that comes with a certain amount of complexity in its internals.

We thought about allowing upcasting a couple of times, but the effort to get that working is simply not worth it, and people would simply abuse the syntax doing very dangerous things.

As stated on DDC-16, it is also indeed not possible to understand which class the property belongs to without incurring in nasty problems such as multiple subclasses defining same properties with different column names.

If you want to filter data in subclasses in a CTI or JTI, you may use the technique that I've described at https://stackoverflow.com/a/14854067/347063 . That couples your DQL with all involved subclasses.

The DQL you would need in your case is most probably (assuming that Entities\Book is a subclass of Entities\Item):

SELECT
    a
FROM
    Entities\Auction a 
INNER JOIN
    a.item i
INNER JOIN
    i.bookTypes b
WHERE
    i.id IN (
        SELECT 
            b.id
        FROM
            Entities\Book b
        WHERE
            b.type = 'Fantasy'
    )

That is the pseudo-code for your problem. It is not nice, but keep in mind that SQL and DQL are very different and follow different rules.