= The queryset-refactor branch =

This branch contains a major refactoring of the {{{django.db.models.query.QuerySet}}} class to fix a group of SQL problems and make SQL generation easier for database backends requiring customization.

== How to get the branch ==

{{{
svn co http://code.djangoproject.com/svn/django/branches/queryset-refactor
}}}

See our [http://www.djangoproject.com/documentation/contributing/#branch-policy branch policy] for full information on how to use a branch.

== Status ==

Branch was created on 13 September, 2007.

At the moment, the branch is fairly unusable. All the tests pass, but there are a lot of other places in the code that attempt to construct SQL fragments and pass them around and they will tend to break.

The focus right now is on correctness, but some significant performance profiling and tuning will need to be done. Current performance is quite a bit slower than the existing code. The good news here is that there are some obvious places to speed things up and, no doubt, some unobvious as well once we get to that point. An optimisation pass is still some way off at the moment; getting all the relevant bugs fixed is the current focus.

Tickets of interest for this branch are marked with ''qs-rf'' (and ''qs-rf-fixed'' when fixed) in the keywords field in Trac. [http://code.djangoproject.com/query?status=new&status=assigned&status=reopened&keywords=%24qs-rf&order=priority This report] shows all the tickets being worked on (To view ''qs-rf'' with the ''qs-rf-fixed'' tagged tickets, [http://code.djangoproject.com/query?status=new&status=assigned&status=reopened&keywords=%7Eqs-rf&order=priority view this report]).

== Changes introduced on the branch ==

A few backwards incompatible changes are created by the changes in this branch. Most people won't be affected by many of these, and porting code is reasonably straightforward.

 * The {{{Options.get_order_sql()}}} method is now gone in {{{django.db.models.options}}}. There appears to be no use for this method any longer.
 * Ordering querysets across related models has a new syntax that is the same as the way you specify relations in a filter: {{{field1__field2__field3}}}, etc. Previously, you had to specify the database table name and the ''model'' field name, separated by a period. This led to some problems with multiple joins, as well as requiring you to remember the database table name, which depended on things like the application name. The new syntax is more natural and consistent, as well as helping solve a few bugs. See the {{{order_by()}}} documentation in db-api.txt for more information and some examples.
 * {{{Q}}} objects have changed internally. This is only relevant if you have created custom Q-like objects. You would have created a {{{get_sql()}}} method that returned a data structure that was inserted into the query. In the new code, you create a {{{add_to_query()}}} method that accepts one argument -- the {{{django.db.models.sql.query.Query}}} instance for the current query. Your Q-like object can then add to the various attributes of this class (`select`, `where`, etc) to have whatever effect it likes on the result. Note that the {{{add_to_query()}}} method is called when the object is added to the {{{Query}}} object and more changes may be made before it is turned into SQL and executed against the database.