id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
25774	Refactor of datetime expressions and better, official support for right-hand-side date part extraction	David Filipovic	Josh Smeaton	"As previously stated in [https://code.djangoproject.com/ticket/25556 this ticket] and [https://groups.google.com/forum/#!topic/django-developers/GU8OrPUMjrc this thread], I have begun work on the following:

   - making the so called datetime transforms (currently residing in `django.db.models.lookups`) part of the officially supported ORM API as part of the db expressions,
   - making these transforms easily usable on the right hand side of lookups / Q objects
[[BR]]


To this effect, I propose the following:
     - replace module `django.db.models.expressions` with a package of the same name
     - add module `django.db.models.expressions.datetimes`
     - rename `XTransform` to `XExtract` and move them from `django.db.models.lookups` to `django.db.models.lookups` to `django.db.models.expressions.datetimes`
     - change `YearLookup` and `YearComparisonLookup` to allow for functions on the right hand side
    - extensive testing of these db expressions
    - adding this to the release notes
    - any other change that might support this

[[BR]]

I'm also adding a [https://github.com/django/django/pull/5683 PR] with some of these already implemented. What remains to be done is:
    - replace references `XTransform` type classes in `django.db.models.lookups` with `XExtract` classes from `django.db.models.expressions.datetimes`
    - replace these references anywhere else in the project (I've noticed there are some in the tests, for instance)

[[BR]]

With the API in the [https://github.com/django/django/pull/5683 PR] it becomes possible to do the following lookup:


{{{
from django.db.models.expressions.datetimes import DateExtract

Person.objects.filter(birth_date__year=DateExtract('job__start_date', lookup_name='year'))
}}}

which is equivalent to:


{{{
from django.db.models.expressions.datetimes import YearExtract

Person.objects.filter(birth_date__year=YearExtract('job__start_date'))
}}}


Additionally, @jarshwah suggested that these should maybe be named: `ExtractX` instead of `XExtract`.
"	New feature	closed	Database layer (models, ORM)	dev	Normal	fixed	db,expressions,date,time,extract,transform 1.10	josh.smeaton@… info+coding@… aksheshdoshi@…	Ready for checkin	1	0	0	0	0	0