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
32944	Simplify where clause creation where the WhereNode is immediately created and then added to and then returned.	Keryn Knight	Keryn Knight	"There are currently 2 places in Django which essentially do:
{{{
where = WhereNode()
where.add(condition, AND)
}}}
and then return the where. 

There are a ''bunch'' of places where a where class is added to and then conditionally added to either immediately or far later in other complex branches, (eg: is it a reffed expression, etc). Those are not for consideration IMHO because the changes would probably add more complexity.

But for those 2 places, `django.db.models.sql.query.Query.build_filter` and `django.contrib.contenttypes.fields.GenericRelation.get_extra_restriction` where the code is respectively:
{{{
clause = self.where_class()
clause.add(condition, AND)
return clause, []
}}}
and
{{{
cond = where_class()
lookup = field.get_lookup('exact')(field.get_col(remote_alias), contenttype_pk)
cond.add(lookup, 'AND')
return cond
}}}
both can be simplified to respectively:
{{{
return self.where_class([condition], connector=AND), []
}}}
and
{{{
return where_class([lookup], connector=AND)
}}}
which end up as the same result, that is:
{{{
x = WhereNode([('a', 1)], connector='AND')
y = WhereNode()
y.add(('a', 1), 'AND')
assert x == y
}}}
but a bit faster. Specifically the proposed form is roughly `550-600ns` per op vs. the unnecessary add which is `650-700ns`:
{{{
In [17]: %%timeit
    ...: x = WhereNode([('a', 1)], connector='AND')
597 ns ± 12.5 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
In [18]: %%timeit
    ...: x = WhereNode()
    ...: x.add(('a', 1), 'AND')
780 ns ± 8.73 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
}}}
Given `build_filter` prevalence (it's called what, at least once per argument to `filter()` or `exclude()` ... maybe more on complex queries?) it's maybe worth having. 

I'll put in a PR shortly to run the bits of the test suite I can't, and boil the ocean on the off-chance that this gets accepted. Naturally if anything fails, we can just move it to invalid without further consideration :)"	Cleanup/optimization	closed	Database layer (models, ORM)	dev	Normal	fixed			Accepted	1	0	0	1	0	0