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
26476	Migration preserve_default does not works properly?	madeng	nobody	"Hi all, I'm using Django<1.9
When i change my model adding a default to one field or adding a new field to existing model with a default, and I launch:

`./manage.py sqlmigrate my_app_label my_migration_name`

I see:

''BEGIN;
ALTER TABLE `my_app_label` ADD COLUMN `my_char_field` varchar(36) DEFAULT test NOT NULL;
ALTER TABLE `my_app_label` ALTER COLUMN `my_char_field` DROP DEFAULT;
COMMIT;''

Reading Docs ([https://docs.djangoproject.com/en/1.8/ref/migration-operations/#alterfield]) i can see, about  that ''preserve_default'', that :

   The preserve_default argument indicates whether the field’s default value is permanent and should be baked into the project state (True), or if it is temporary and just for this migration (False) - usually because the migration is altering a nullable field to a non-nullable one and needs a default value to put into existing rows. It does not affect the behavior of setting defaults in the database directly - '''Django never sets database defaults and always applies them in the Django ORM code'''.

So why I see launching sqlmigrate **DEFAULT** and than **DROP DEFAULT** ?
For large databases this could be an heavy pair of query.

Best Regards
"	Bug	closed	Migrations	1.8	Normal	invalid	preserve_default sqlmigrate	g.bottalico@…	Unreviewed	0	0	0	0	0	0