Doctrine query distinct related entity

Question

I'm probably overlooking something very simple and just been staring at it too much, but I can't get this DQL query to work. I get an exception stating:

Cannot select entity through identification variables without choosing at least one root entity alias.

Here's my query. User has a many-to-one relation to Group. Note that this is a unidirectional relation! That may make no sense to you, but it makes sense in our domain logic.

SELECT DISTINCT g
FROM Entity\User u
LEFT JOIN u.group g
WHERE u.active = :active

Can you tell me what I am missing here?

Answer 1

Since this is the first Google match when searching for the error message "Cannot select entity through...", I decided to respond despite the topic was posted few months ago.

The trick is to use JOIN ... WITH ... (like JOIN ... ON ... in SQL).

I was having the message with this code:

SELECT ro, COUNT(ro)
FROM FH\MailerBundle\Entity\Recipient r
JOIN r.selectedOption ro
GROUP BY ro.id

I solved the problem by this code:

SELECT ro, COUNT(ro)
FROM FH\MailerBundle\Entity\RecipientOption AS ro
JOIN FH\MailerBundle\Entity\Recipient AS r WITH r.selectedOption = ro
GROUP BY ro.id

I needed to specify full namespaces and classes for both entities.

Answer 2

You need to select FROM the root entity alias.. meaning you can't SELECT only from a table you're joining on, as you can in plain sql.. so something like this should do it:

SELECT DISTINCT g
FROM Entity\Group g
INNER JOIN g.user u
WHERE u.active = :active

Answer 3

I worked around the problem by doing a subselect:

SELECT g
FROM Entity\Group
WHERE g.id IN (
    SELECT DISTINCT g2.id
    FROM Entity\User u
    LEFT JOIN u.group g2
    WHERE u.active = :active
)