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
27021	Add explicit support for Q object annotations	Josh Smeaton	Ian Foote	"A common pattern that has arisen with expressions is to annotate a Q object to the query without going through the Case/When ceremony.

{{{
Model.objects.annotate(boolfield=ExpressionWrapper(Q(field__gte=4), output_field=BooleanField()))
}}}

We've tried to discourage this pattern because the Case/When structure is a lot more powerful and correct. Sometimes the power isn't required and users really just want to annotate a boolean expression. Q objects and the WhereNode it resolves to aren't really proper expressions, but they could be. Case/When uses Q objects internally, which is why it's important to test Case/When for any major changes to Q and WhereNode.

Explicit support for Q object annotations should implement an implicit BooleanField as the output_field. I believe this is only required on the WhereNode since that is what is ultimately resolved. Once this happens, the above query becomes a lot nicer.

{{{
Model.objects.annotate(boolfield=Q(field__gte=4))
}}}

For this to work the following is definitely required:

- Add an `output_field=BooleanField()` to `WhereNode`
- Add a `resolve_expression()` to `WhereNode` (unsure what this should return - requires significant testing with Case/When)

Might be required:

- Add an `output_field=BooleanField()` to `Q`

Tests:

- Adding a subquery containing a Q annotation to a parent query
- Adding a subquery containing a Case/When annotation to a parent query (if it's not already tested)
- Standard tests that most other annotations already implement
- Nullable fields used in Q annotations"	New feature	closed	Database layer (models, ORM)	dev	Normal	fixed		josh.smeaton@… Ryan Hiebert Balazs Endresz Matthijs Kooijman Petr Přikryl Ian Foote	Ready for checkin	1	0	0	0	0	0