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
14373	annotate() will gladly delete your data	Patryk Zawadzki	Carl Meyer	"Consider the following example:

{{{
class Foo(models.Model):
    name = models.CharField(max_length=100)

class Bar(models.Model):
    name = models.CharField(max_length=100)
    foos = models.ManyToManyField(Foo, related_name='bars')
}}}

Create your database, fill it with important data, then do the following:

{{{
bars = Bar.objects.all().annotate(foos=Sum('foos'))
}}}

Now all your data connections are gone. Yay.

What happens is that {{{annotate}}} gladly accepts ""foos"" even if that attribute name is already taken. It then retrieves all the objects from the result set and proceeds to destroy your data by assigning aggregated values to your precious related manager. The manager then happily swallows the integer it receives and goes to delete all the relations.

Possible fixes:
 * Make {{{annotate}}} call {{{delattr}}} before calling {{{setattr}}}
 * Make {{{annotate}}} raise an exception when passed an already existing attribute

Also:
 * Make the many-to-many manager think for a while before it accepts 5 or any other integer as the new relation set"		closed	Database layer (models, ORM)	1.2		duplicate			Accepted	0	0	0	0	0	0