I've had my share of confusion over delete. Here's a thread that I had with Malcolm recently:
http://groups.google.com/group/django-users/browse_thread/thread/582f21486c1073eb/7f5743953047d9fa?lnk=raot&fwc=1 However, I guess I'm still quite confused. One thing I don't understand is when the "bulk delete" happens. I thought, for example, that it happened when one uses the queryset delete. So I just wrote myself a little test. Here's the model. I have a 'Book' and it has readers (that have ForeignKey back to Book) class Publisher(models.Model): name = models.CharField(max_length=100) class Book(models.Model): title = models.CharField(max_length=100) publisher = models.ForeignKey(Publisher, blank=True, null=True) class Reader(models.Model): book = models.ForeignKey(Book, blank=True, null=True) name = models.CharField(max_length=100) Here's a small snippet of code that creates a book with two readers. I then delete the book using a queryset delete. I thought that in this case neither Book.delete() nor Reader.delete() would get called. However, the output indicates that preDeleteCallBack() does get called, once for the deletion of book1, and once for each of the two reader objects. def preDeleteCallBack(sender, instance=None, **kwargs): print "PreDelete called for instance", instance pre_delete.connect(preDeleteCallBack, sender=Reader) pre_delete.connect(preDeleteCallBack, sender=Book) pub1 = Publisher.objects.create(name="pub1") book1 = Book.objects.create(title="book1", publisher=pub1) reader1 = Reader.objects.create(name="reader1", book=book1) reader2 = Reader.objects.create(name="reader2", book=book1) Book.objects.filter(title="book1").delete() The output from this call to delete() is: PreDelete called for instance book1 PreDelete called for instance Reader object PreDelete called for instance Reader object In my app, I use a lot of formsets. I thought that bulk delete got used for those. Yet again, when I tested it using a little debug app I find that the preDeleteCallBack() function gets called. For example: bookPostDict = { 'form-INITIAL_FORMS': u'1', 'form-TOTAL_FORMS': u'1', 'form-0- title': u'book1', 'form-0-DELETE': u'on', 'form-0-id': u'1', 'form-0- publisher': u'1', } bookFormSet = BookFormSet(data=bookPostDict) if bookFormSet.is_valid(): bookFormSet.save() When bookFormSet.save() gets executed, I get this output: PreDelete called for instance book1 PreDelete called for instance Reader object PreDelete called for instance Reader object So I guess I am totally confused now. I know I have had a ton of problems with my foreignKey objects getting deleted when the thing they point to gets deleted. Based on Malcolm's response in the thread above, it certainly seemed like I was in bulk delete territory, but using these pruned down examples I find I can't even get a bulk delete to happen. George, would you be able to clarify when the bulk delete happens? I see in the doc that it says: "Keep in mind that this will, whenever possible, be executed purely in SQL, and so the delete() methods of individual object instances will not necessarily be called during the process." Perhaps in my queryset delete I am not hitting the case where bulk delete will be called? I am also interested particularly in formsets and what happens when can_delete is True and what happens when the delete occurs as a result of doing a formset save() when some objects have been targeted for deletion. Sorry for the length of this. I've spent all morning trying to grock this and am disappointed that my debugging work has resulted in me being even more confused than before! Margie On May 9, 8:33 am, George Song <geo...@damacy.net> wrote: > On 5/9/2009 7:14 AM, Rune Bromer wrote: > > > > > Hi, > > > I run a small project handling payments from users. Each user has the > > possibility to delete their account and if they do I have to keep > > their payment data. Also, I would like to disable admins from deleting > > the data as there are NEVER a valid reason to do so. The payment model > > has foreign keys so obviously I need to set these to None before I > > delete the instances ref'ed by the payment. I do this in a pre_delete > > () signal for all the models ref'ed by the payment model. > > > Also, I created a delete() method on the payment model that will not > > call the supers delete() when the payment is complete. > > > The only thing missing is the admin. As I understand the admin will > > send a pre_delete() signal so hopefully it will not find the payment > > objects when deleting a user because the link will go away in the > > signal. What I'm more worried about is if a stupid admin tries to > > delete the payment objects themselves. I can remove the actions of > > cause, but how about the per-object delete functionality? Removing the > > permission will not work for people having is_superuser = True. > > > Hope the problem is understandable. Hopefully I'm overlooking > > something simple? > > If you already did an override on `Payment.delete()`, then you should be > fine. > > Although be mindful of bulk delete, as it doesn't use `Model.delete()`: > <http://code.djangoproject.com/ticket/11022> > > Also you might want to think about setting up a group in auth to have > finer grained permission control. It's pretty simple to just leave out > delete for this specific model. Is there a reason they need to be > superusers? > > -- > George --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. 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