I've already started this topic in django-users (
https://groups.google.com/forum/#!topic/django-users/k9K7VsPe6aA) and got
an advice there to ask here.
It's not a big issue and it can be solved quite easily as I can see from
django sources. Also there're some workarounds to deal with it but I write
here coz I thinks that it makes django behaviour inconsistent.
So we have 2 models:
class Group(models.Model):
name = models.CharField()
class Meta:
ordering = ('name',)
class Entity(models.Model):
group = models.ForeignKey(Group, null=True)
Now I want to perform a really simple query like this (to order by group_id
field itself):
SELECT * FROM `app_entity` ORDER_BY `app_entity`.`group_id` ASC;
So we use smth like that:
Entity.objects.order_by('group')
and get (not a big surprise, it's well documented behaviour):
SELECT * FROM `app_entity`
LEFT OUTER JOIN `app_group` ON ( `app_entity`.`group_id` = `app_group`.`id`
)
ORDER BY `app_group`.`name` ASC
The only way to get rid of JOIN is to remove ordering attribute from Group
Meta class. But it's not a solution coz it's used in many other places.
So the inconsistency is that we have 2 different behaviours with and
without ordering attribute in related model.
When we don't have ordering defined we can easily order by the field itself
as well as order by any field in related model if we need to.
While when it's defined we loose the way to order by the field itself
(still can use extra or even explicitly specify table name but it's all
quite ugly).
Quite obvious solution is to use `order_by('group_id')` for explicit field
ordering.
But in django<1.7 trying to order by `order_id` raises FieldError. In 1.7
order_by('group_id') became identical to order_by('group').
So if 1.7 is released with that new behaviour it will become
backwards-incompatible to use `order_by('group_id')` for this purpose.
Related topic: #19195 <https://code.djangoproject.com/ticket/19195>
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