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
29185	Migrations with `default=some_callable` populate all existing rows with the same value	Stavros Korokithakis	nobody	"A migration that adds a field with `default=some_func` run that function once and then use the value as the default for the new rows. This fact is [documented](https://docs.djangoproject.com/en/2.0/howto/writing-migrations/#migrations-that-add-unique-fields), though still surprising.

I propose that `makemigrations` either issues a warning when a field with a `default=callable` is encountered, or, better yet, that it asks what the user intends and generates the three-step migration in the documentation instead. An acceptable solution would also be to generate the three-step migration without asking and then warn about slowness, as that is more in line with users' expectations."	Bug	closed	Migrations	2.0	Normal	duplicate			Unreviewed	0	0	0	0	0	0