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
31368	"Document Field.from_db_value()'s ""expression"" parameter."	Paolo Lammens	Hasan Ramezani	"The documentation on the semantics and usage for the `expression` parameter in the [https://docs.djangoproject.com/en/3.0/ref/models/fields/#django.db.models.Field.from_db_value `from_db_value` converter] is nowhere to be found.

The only two places that mention this method are the [https://docs.djangoproject.com/en/3.0/ref/models/fields/#django.db.models.Field.from_db_value Model field reference] and the [https://docs.djangoproject.com/en/3.0/howto/custom-model-fields/#converting-values-to-python-objects ""Writing custom model fields"" guide], but neither mention what `expression` is or how it should be used. 

In fact, there is no specification for `value` or `connection` either, but at least the meaning of these parameters can be inferred.


See also: https://stackoverflow.com/q/60560775/6117426"	Cleanup/optimization	closed	Documentation	3.0	Normal	fixed	documentation, missing		Ready for checkin	1	0	0	0	1	0