A custom ordering SQL and Django models

[Daybreaker]

I want to run a query like this:

select * from bbs_article a, bbs_article_tags a2, bbs_tag t where t.id
= a2.tag_id and a.id = a2.article_id order by (case when t.name =
'notice' then '' else t.name end)

which has a custom ordering rule.

As far as I know, Django model currently does not support such custom
orderings, but only field-based native orderings.

How do I use the above sql in most clear way (like using typical model
query with manually changed order clause), or is there any workaround
to do the same jobs?

[Daniel Roseman]

Sounds like the queryset .extra() method with the order_by parameter
might help.
http://docs.djangoproject.com/en/dev/ref/models/querysets/#extra-select-none-where-none-params-none-tables-none-order-by-none-select-params-none
--
DR.

[Daybreaker]

Finally I implemented a custom manager.

http://dpaste.com/hold/75010/

But another problem arised, that Django's object_list generic view
only accepts a QuerySet object, not list neither other iterables.
Of course I can implement my own pagination with the given Paginator
class, but this seems not so much clean...

[Daybreaker]

I've tried that also, but it ALSO only accepts field names. Its
intention to be there is not to override previously set order clauses.

> might help.http://docs.djangoproject.com/en/dev/ref/models/querysets/#extra-sele...
> --
> DR.

[krylatij]

Use extra() method of query set with little hack ;)

mymodel.objects.extra(select={'ordering_field': 'IF(STRCMP
(bbs_tag.name, 'notice'), '',bbs_tag.name)'},
order_by=['ordering_field'])

[Daybreaker]

Thanks, that works! (but I already changed my implementation not to
use tag-based ordering...)
For more generality, you could replace bbs_tag with Tag._meta.db_table
value.