[Django] #27332: Specifying additional JOIN arguments

[Django]

#27332: Specifying additional JOIN arguments
----------------------------------------------+--------------------
     Reporter:  MikiSoft                      |      Owner:  nobody
         Type:  Uncategorized                 |     Status:  new
    Component:  Database layer (models, ORM)  |    Version:
     Severity:  Normal                        |   Keywords:
 Triage Stage:  Unreviewed                    |  Has patch:  0
Easy pickings:  0                             |      UI/UX:  0
----------------------------------------------+--------------------
 For example, this raw SQL:
 {{{
 SELECT event.*
 FROM event
 INNER JOIN
     business
     ON (event.business_id = business.id AND business.manager_id = 1)
 LEFT JOIN
     'like'
     ON (event.id = object_id AND content_type_pk = 17 AND person_id = 1)
 ORDER BY COALESCE('like'.date, event.'when') DESC;
 }}}

 Can't be translated to equivalent Django ORM expression even if using
 `extra()` command, because there isn't anywhere a possibility to set
 additional arguments on `JOIN` clauses. And when I'm using
 `filter(Q(argument) | ...)` it happens to always push all arguments to
 `WHERE` clause, which just causes a performance hit. I wish there was some
 parameter which would determine the destination of the argument, whether
 it has to go to the (last) `JOIN` clause, or to be put in `WHERE` (which
 goes by default). Also, I'm not able to comprehend how to perform
 correctly `LEFT JOIN` so in the end I have made some jumbled up expression
 which is completely inefficient (as it executes two queries, but it's the
 only way to do the same from above and get `QuerySet` in return):

 {{{
 from django.db.models import Q, Coalesce

 Event.objects.filter(Q(pk__in=Like.objects.filter(person__pk‌​‌​=1,
 
content_type=17).prefetch_related('content_object').values_l‌​‌​ist('object_id',
 flat=True)) | Q(business__manager=1)).order_by(Coalesce('likes__date',
 'when').desc())
 }}}

 I'm filing this issue because some (or many?) people like me desperately
 need output in a form of a `QuerySet` because of the pagination and many
 other things `RawQuerySet` doesn't support, so using `raw()` isn't
 definitely an option in my case. Django has left me out of choice.

--
Ticket URL: <https://code.djangoproject.com/ticket/27332>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.

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