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
26539	Using Annotation As Update Parameter Generates Invalid SQL.	David Sanders	PREMANAND	"If you try to use an annotation which spans tables in an update, everything will resolve and attempt to execute but the SQL will fail because for MySQL the query is broken into a `SELECT` and then an `UPDATE`, but the necessary info is not available in the UPDATE. On sqlite3 it generates an `UPDATE` that looks similar but with the `SELECT` as a subquery.

Example:

{{{
class Bar(models.Model):
    name = models.CharField(max_length=32)

class Foo(models.Model):
    related_bar = models.ForeignKey(Bar)
    bar_name = models.CharField(max_length=32)

Foo.objects.annotate(related_bar_name=F('related_bar__name')).update(bar_name=F('related_bar_name'))
}}}

On MySQL produces:

{{{
SELECT `test_foo`.`id`, `test_bar`.`name` AS `bar_name` FROM `test_foo` LEFT OUTER JOIN `test_bar` ON ( `test_foo`.`related_bar` = `test_bar`.`id` );

UPDATE `test_foo` SET `bar_name` = `test_bar`.`name` WHERE `test_foo`.`id` IN (1);
}}}

I don't think there's a trivial fix for this. Doing an `UPDATE` with a `JOIN` appears to have different syntax in the various implementations and isn't possible at all on sqlite3, so it would need to be multiple queries.

Seems that until it can be made to work correctly an error should occur if attempted, similar to the [https://github.com/django/django/blob/master/django/db/models/sql/compiler.py#L1098 error for aggregates] in an `UPDATE`."	Bug	closed	Database layer (models, ORM)	dev	Normal	duplicate			Accepted	0	0	0	0	0	0