Solved
I was culling children based on redundancy but a missing child was being
automatically inserted again. The error was being correctly reported as
a DoesNotExist problem but until I noticed the incremented pk in the
database I was looking in the wrong places.
Thanks again for your effort - I'm sorry to waste your time.
Mike
On 6/02/2013 2:14pm, Mike Dewhirst wrote:
Pankaj, thank you
I have tried the code in a number of ways - including the way you wrote
it[1] - and located in either Master[2] or Parent and it always runs to
completion without raising its own exception. It happily prints out
progress flags in the dev server and then finally delivers the 500
ValidationError mentioned below.
My conclusion is the Admin doesn't like me.
My code (equivalent with yours) seems to be working but the entire
transaction seems to be getting rolled back when it is nearly finished.
I think it must be something to do with the data so I'm simplifying as
hard as I can and ...
I'm currently studying the traceback - which is *all* Django code and
none of mine.
More later
Thanks again.
Mike
[1] Your version was what I tried first because that is what the docs
illustrate. I eventually used the list to make sure the query_set
actually ran and I was deleting actual objects. I have now gone back to
the way you wrote it because I'm convinced the problem is elsewhere.
[2] It now lives in the Master and is called with the 'mark' from the
Parent on the pre-delete signal. I do this despite using pre-delete
because of the warning in docs about deleted objects trying to do
things. I know the Master won't be deleted.
On 6/02/2013 4:57am, Pankaj Singh wrote:
Hey Mike,
I tried to replicate what you were trying to do and I got it working.
By the way, you can directly delete filtered child objects, no need to
create a list. And you don't need to create a list for iterating over a
queryset.
Queryset supports iteration by
default(https://docs.djangoproject.com/en/dev/topics/db/queries/#querysets-are-lazy).
Here is models.py:
|from django.dbimport models
from django.db.models.signalsimport pre_delete
from django.dispatchimport receiver
class Master(models.Model):
name= models.CharField(max_length=200)
def __unicode__(self):
return self.name
class Parent(models.Model):
name= models.CharField(max_length=200)
master= models.ForeignKey(Master)
mark= models.CharField(max_length=40)
def __unicode__(self):
return self.name
def clean_out(self):
Child.objects.filter(master=self.master,
tags=self.mark).delete()
child_lst= Child.objects.filter(master=self.master,
tags__contains=self.mark)
for child in child_lst:
marks= child.tags.split()
marks.remove(self.mark)
child.tags= ''.join(marks)
child.save()
class Child(models.Model):
name= models.CharField(max_length=200)
tags= models.TextField()
master= models.ForeignKey(Master)
def __unicode__(self):
return self.name
@receiver(pre_delete, sender=Parent)
def parent_delete_handeler(sender, instance, *args, **kwargs):
instance.clean_out()|
Sincerely,
Pankaj Singh
http://about.me/psjinx
On Tue, Feb 5, 2013 at 12:15 PM, Mike Dewhirst <mi...@dewhirst.com.au
<mailto:mi...@dewhirst.com.au>> wrote:
Could someone please point out my mistake?
def clean_out(self):
child_lst = list(Child.objects.filter(__master=self.master,
tags=self.mark))
for child in child_lst:
child.delete()
child_lst = list(Child.objects.filter(__master=self.master,
tags__contains=self.mark))
for child in child_lst:
marks = child.tags.split()
marks = marks.remove(self.mark)
child.tags = ' '.join(marks)
child.save()
The "self" in this case is an instance of the Parent class and
clean_out() is a Parent model method. Both Parent and Child have a
foreign key relationship with the Master model. Nothing has a
foreign key pointing to either Parent or Child.
Parent.clean_out() method is connected to the pre_delete signal of
the Parent model.
The purpose of the method is more or less documented below.
I've tried this a number of different ways and always get the
"Select a valid choice ..." error mentioned below.
On 4/02/2013 6:14pm, Mike Dewhirst wrote:
This is the error ... Select a valid choice. That choice is not
one of
the available choices.
I want to delete a bunch of "child" records when a "parent"
record is
deleted. While I'm using that terminology they are not actually
related
in the usual sense. All however are in foreign key relationships
with
the same owner/master.
The child records all know which parents they have because the
parent
added its mark to a field in the child when the child record got
created
and linked to the master. In fact if that child had been added by
another parent, the next parent just adds its mark instead of
adding
another child.
When a parent gets deleted from the master, its mark is removed
from all
the child records it was involved with and if it was the only
mark the
child gets deleted too. Or at least that is what I want to
happen.
My question is:
In overview, how should I be doing this?
At the moment I'm trying to do it all via model methods calling
various
managers because it feels like the right place to do it.
I have tried to make a custom manager with
use_for_related_fields = True
but still get the same error.
Thanks for any help
Mike
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