subquery in join with doctrine dql - doctrine-orm

Question

I want to use DQL to create a query which looks like this in SQL:
select
e.*
from
e
inner join (
select
uuid, max(locale) as locale
from
e
where
locale = 'nl_NL' or
locale = 'nl'
group by
uuid
) as e_ on e.uuid = e_.uuid and e.locale = e_.locale
I tried to use QueryBuilder to generate the query and subquery. I think they do the right thing by them selves but I can't combine them in the join statement. Does anybody now if this is possible with DQL? I can't use native SQL because I want to return real objects and I don't know for which object this query is run (I only know the base class which have the uuid and locale property).
$subQueryBuilder = $this->_em->createQueryBuilder();
$subQueryBuilder
->addSelect('e.uuid, max(e.locale) as locale')
->from($this->_entityName, 'e')
->where($subQueryBuilder->expr()->in('e.locale', $localeCriteria))
->groupBy('e.uuid');
$queryBuilder = $this->_em->createQueryBuilder();
$queryBuilder
->addSelect('e')
->from($this->_entityName, 'e')
->join('('.$subQueryBuilder.') as', 'e_')
->where('e.uuid = e_.uuid')
->andWhere('e.locale = e_.locale');

Answer 1

You cannot put a subquery in the FROM clause of your DQL.
I will assume that your PK is {uuid, locale}, as of discussion with you on IRC. Since you also have two different columns in your query, this can become ugly.
What you can do is putting it into the WHERE clause:
select
e
from
MyEntity e
WHERE
e.uuid IN (
select
e2.uuid
from
MyEntity e2
where
e2.locale IN (:selectedLocales)
group by
e2.uuid
)
AND e.locale IN (
select
max(e3.locale) as locale
from
MyEntity e3
where
e3.locale IN (:selectedLocales)
group by
e3.uuid
)
Please note that I used a comparison against a (non empty) array of locales that you bind to to the :selectedLocales. This is to avoid destroying the query cache if you want to match against additional locales.
I also wouldn't suggest building this with the query builder if there's no real advantage in doing so since it will just make it simpler to break the query cache if you add conditionals dynamically (also, it's 3 query builders involved!)