= The queryset-refactor branch = (Up to date as of 22 March, 2008) 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 should be fairly usable for people wishing to test (with the exception of the Oracle backend, as noted below). It is not appropriate for production usage. Some of the new features, such as model inheritance still have rough edges or are incomplete, but all the porting work is complete and code that fixed existing bugs should all work. There are still some internal changes that need to be made prior to merging with trunk, so any code that tries to rely on internal methods may need to change before the next release. Bug reports against code '''not''' listed in the [#Workinprogress work in progress] section should be filed in Trac. Please take some extra effort to check for duplicates first. 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]). == New features == Along with, and as part of, all the bug fixes mentioned above there are a number of new features in the branch. A number of these features are purely internal details, but there are a few that add extra public functionality. 1. 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. 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. 2. Model inheritance is now possible. Both abstract base classes and multi-table inheritance are possible. See the model-api.txt documentation for details. 3. The {{{__iter__()}}} method on querysets does not pull all the results into memory immediately. This reduces memory usage for large querysets where you don't end up accessing all the results. Queryset caching still occurs, though, so a single queryset object will only hit the database once. This change means that testing the boolean value of a queryset will only pull in the first few rows of the result, not all of them. 4. Slicing a queryset from a particular value to the end of a queryset is possible. 5. Querysets have a {{{reverse()}}} method that reverses whatever the current ordering is. 6. The queryset {{{values()}}} method can retrieve fields that are related via a {{{ForeignKey}}} or {{{OneToOneField}}} relation. 7. A new {{{valueslist()}}} method has been added to querysets. This is similar to {{{values()}}} except that it returns a list of tuples, rather than a list of dictionaries. 8. You can specify a list of related fields to traverse in a {{{select_related()}}} call. This provides a way to select only the related data you are interested in. Only single-valued relations can be selected in this way, however (not {{{ManyToManyFields}}}). 9. Filtering a queryset by checking if a field attribute is {{{None}}} is equivalent to testing if the corresponding database column is {{{NULL}}}. So {{{qs.filter(foo=None)}}} is now identical to {{{qs.filter(foo__isnull=True)}}}. 10. An {{{update()}}} method has been added to querysets to allow multiple objects to have an attribute updated in a single SQL query. == Backwards incompatible changes == 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. * {{{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. * The {{{OneToOneField}}} class has finally been updated, as the documentation has indicated would be happening for a long while. There are few externally visible changes, with one exception: a {{{OneToOneField}}} is no longer automatically the primary key for a model that includes it. It still accepts the {{{primary_key}}} attribute, however, so you should add {{{primary_key=True}}} to the declaration of any existing {{{OneToOneField}}} instances in your code to preserve backwards compatibility. * If you pass a bad field name into a filter or {{{order_by()}}}, Django now raises {{{FieldError}}} (from {{{django.core.exceptions}}}), rather than Python's built in {{{TypeError}}}. Also, the list of legal field names is now sorted alphabetically for easier searching. This should have no effect on most production code, however some test suites may need to be updated to accommodate the changed traceback output. * It is possible to use extra select fields -- those included via {{{extra(select=...)}}} -- for ordering the results. Previously, those fields could be specified to the {{{order_by()}}} method. Due to increased error checking, that is no longer practical. Instead, pass those extra columns to the {{{order_by}}} argument of the {{{extra()}}} method: {{{ #!python qs.extra(select={'a': ...}).order_by('a') # Old style qs.extra(select={'a': ...}, order_by=('a',)) # New style }}} * Still on {{{extra(select=...)}}}... if you want to substitute parameters into these extra selection columns, use the {{{select_params}}} argument to {{{extra()}}}. The {{{params}}} arumgent is only applied to the extra where conditions. * {{{select_related(False)}}} is no longer possible. Don't worry. You didn't know this existed, so you won't miss it. It was never part of the official API. * There is a slight difference between these two filter statements {{{ #!python qs.objects.filter(f1).filter(f2) qs.objects.filter(f1, f2) }}} This difference only applies when `f1` and `f2` are referencing the same multi-valued relationship (a `ManyToManyField` or reverse `ForeignKey`). The first version allows filtering against different items from the relationship (things that match `f1` on one object in the related table as well as `f2` on another object in the related table), whereas the second version's filters will be applied to the same item. See the database API documentation section called "Lookups that span relationships" for details. == Work in progress == If you are testing this branch, there are a few areas that need caution. These are known places that are work-in-progress, so expecting them to work perfectly (or even at all) would be optimistic. Obviously, in addition to these points there are a lot of little things being tweaked and fixed, as well as optimisation work going on. That's to be expected on a branch. * Model inheritance has not been integrated into the admin. It's unclear at this time whether it will be worth doing this for existing admin or just port straight to newforms-admin. In any case, trying to use multi-table inheritance via the admin interface won't work. * {{{OneToOneField}}} in the admin interface has similar problems.