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
25693	Data loss if a ManyToManyField is shadowed by Prefetch	Ian Foote	nobody	"With two models:

{{{#!python
class Book(Model):
    name = CharField(max_length=100)

class Author(Model):
    books = ManyToManyField(Book)
}}}

it is possible to create a prefetch query that loses data from Author.books:

{{{#!python
poems = Book.objects.filter(name='Poems')
Author.objects.prefetch_related(
    Prefetch('books', queryset=poems, to_attr='books'),
)
}}}

When this queryset is evaluated, each Author's books is overridden by the poems queryset."	Bug	new	Database layer (models, ORM)	master	Normal				Unreviewed	0	0	0	0	0	0