Re: [Django] #26706: ManyToMany clear doesn't clear the items from the object but deletes from db

[Django]

#26706: ManyToMany clear doesn't clear the items from the object but deletes 
from
db
-------------------------------------+-------------------------------------
     Reporter:  cosmosgenius         |                    Owner:  nobody
         Type:  Bug                  |                   Status:  new
    Component:  Database layer       |                  Version:  1.8
  (models, ORM)                      |
     Severity:  Normal               |               Resolution:
     Keywords:  manytomany, m2m,     |             Triage Stage:
  clear                              |  Unreviewed
    Has patch:  0                    |      Needs documentation:  0
  Needs tests:  0                    |  Patch needs improvement:  0
Easy pickings:  0                    |                    UI/UX:  0
-------------------------------------+-------------------------------------
Changes (by cosmosgenius):

 * status:  closed => new
 * resolution:  worksforme =>


Old description:

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

> class Tag(models.Model):
>     tag = models.CharField(max_length=100)
>     medias = models.ManyToManyField(Media)
>
>     def __unicode__(self):
>         return self.tag
> }}}
>
> Assume tag object below already has three items of Media model in medias
> which are saved in db. [m1, m2, m3].
>
> {{{
> tag = Tag.objects.get(id=1)
> tag.medias.clear()
> print(tag.medias.all())
> }}}
>
> The above code prints all the three [m1, m2, m3]. Fetching the tag again
> using get and printing givens an empty list "[ ]"

New description:

 {{{

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


 class Tag(models.Model):
     tag = models.CharField(max_length=100)
     medias = models.ManyToManyField(Media)

     def __unicode__(self):
         return self.tag
 }}}

 Assume tag object below already has three items of Media model in medias
 which are saved in db. [m1, m2, m3].

 {{{
 tag = Tag.objects.get(id=1)
 tag.medias.clear()
 print(tag.medias.all())
 }}}

 The above code prints all the three [m1, m2, m3]. Fetching the tag again
 using get and printing givens an empty list "[ ]"

 Failing Testcase

 {{{
 class Test(TestCase):
     def test(self):
         tag = Tag.objects.create(tag='Tag')
         tag.medias.create(name='A')
         tag.medias.create(name='B')
         tag.medias.create(name='C')
         tag = Tag.objects.prefetch_related('medias').get(id=1)
         tag.medias.clear()
         print(tag.medias.all())
 }}}

 I guess its related to prefetch_related function.

--

Comment:

 {{{
 class Test(TestCase):
     def test(self):
         tag = Tag.objects.create(tag='Tag')
         tag.medias.create(name='A')
         tag.medias.create(name='B')
         tag.medias.create(name='C')
         tag = Tag.objects.prefetch_related('medias').get(id=1)
         tag.medias.clear()
         print(tag.medias.all())
 }}}

--
Ticket URL: <https://code.djangoproject.com/ticket/26706#comment:2>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.

-- 
You received this message because you are subscribed to the Google Groups 
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to django-updates+unsubscr...@googlegroups.com.
To post to this group, send email to django-updates@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/django-updates/070.20ac0a493db239631a6013f59d92b93f%40djangoproject.com.
For more options, visit https://groups.google.com/d/optout.