Are django signals also included inside of the transaction.atomic decorator?

Question

I have a model file that uses a post_save signal to create a linked row in another table. In typical fashion, I can create a page from one of my views which is decorated with @transaction.atomic.

I would like to know if this decorator will put the creation of the Page object and the SharedPage object in the same transaction. It is not clear from the django docs that signals are a part of this atomic transaction.

models.py

class Page(models.Model):
    name = models.CharField(default='My default page',max_length=200,blank=False)
    created_at = models.DateTimeField(auto_now_add=True)
    owner = models.ForeignKey(User, on_delete=models.CASCADE)
    slug = models.SlugField()
    uuid = models.UUIDField(default=uuid.uuid4, editable=False)
    is_public = models.BooleanField(default=False)

    def __str__(self):              # __unicode__ on Python 2
        return self.name

    class Meta:
        ordering = ['position','created_at']

@receiver(post_save, sender=Page)
def create_shared_page_entry(sender, instance, created, **kwargs):
    if created:
        shared_page = SharedPage.objects.create(
            page=instance,
            user=instance.user,
            can_edit=True
        )

view.py

@require_http_methods(["POST"])
@transaction.atomic
def page_create(request):
    name = request.POST.get('name')
    page = Page.objects.create(name=name, owner=request.user)

    data = serializers.serialize("json", [page])
    return HttpResponse(data, content_type='application/json')

score 20 · Accepted Answer · answered Jan 07 '17 at 13:40

Yes, signals are dispatched with the same value for autocommit setting of connection(which is tweaked by transaction.commit decorator), which is used to save model. Referring the code in django.db.models.base.Model.save_base() method,

    if not meta.auto_created:
        signals.pre_save.send(sender=origin, instance=self, raw=raw, using=using, update_fields=update_fields)

    with transaction.atomic(using=using, savepoint=False):
        if not raw:
            self._save_parents(cls, using, update_fields)
        updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
    # Store the database on which the object was saved
    self._state.db = using
    # Once saved, this is no longer a to-be-added instance.
    self._state.adding = False

    # Signal that the save is complete
    if not meta.auto_created:
        signals.post_save.send(sender=origin, instance=self, created=(not updated),update_fields=update_fields, raw=raw, using=using)

As you can see, no special code is written to change autocommit settings. So, if your view declares that all the database-related stuff must ensure atomicity by using @transaction.atomic, then db changes made by your view(either model.save() or through signal handlers), is not committed, until your view execution is finished.

I hope, it may help you out.

What if I don't decorate my view function and use context managers `with transaction.atomic():` for object creation? Does it have the same effect? — Masked Man, Dec 16 '21 at 16:01

Are django signals also included inside of the transaction.atomic decorator?

1 Answers1

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