Query Expressions support

[aidsoid]

From Django documentation https://docs.djangoproject.com/en/1.11/ref/models/querysets/#order-by

You can also order by query expressions by calling asc() or desc() on the expression:
Entry.objects.order_by(Coalesce('summary', 'headline').desc())

Or another example from documentation https://docs.djangoproject.com/en/1.11/ref/models/expressions/#some-examples

# Expressions can also be used in order_by()
Company.objects.order_by(Length('name').asc())
Company.objects.order_by(Length('name').desc())

But when I try to use code like this:

sort = ['-some_field_name', Length('some_field_name').asc()]
current_obj = SomeModel.objects.get(pk=current_pk)
some_qs = SomeModel.objects.all().order_by(*sort)
prev_obj = prev_in_order(current_obj, qs=some_qs)

I get an error:
'OrderBy' object does not support indexing
in this file https://github.com/gregplaysguitar/django-next-prev/blob/master/next_prev.py in line 49
if field[0] == '-':

Could you please add support of Query Expressions and fix it?

[aidsoid]

Test example:

    def test_custom_with_query_expression(self):
        qs = Post.objects.all().order_by(Length('text').desc())
        first = qs.first()
        self.assertEqual(first, self.post3)

        second = next_in_order(first, qs)
        self.assertEqual(second, self.post1)

[gregplaysguitar]

Ok - that's a great suggestion, I haven't got time right now but I'll see what I can do in the next few weeks.

In this case though, could you not just go something like this?

Entry.objects.order_by('-summary', '-headline')

[aidsoid]

Coalesce('summary', 'headline').desc() - it's just an example of "Query Expression" from the documentation. In my case I need to sort by length of text inside a field Length('text').desc(). Thanks for support.

[gregplaysguitar]

Ah ok, that makes sense.