Django: Overriding the save() method: how do I call the delete() method of a child class
- by Patti
The setup =
I have this class, Transcript:
class Transcript(models.Model):
body = models.TextField('Body')
doPagination = models.BooleanField('Paginate')
numPages = models.PositiveIntegerField('Number of Pages')
and this class, TranscriptPages(models.Model):
class TranscriptPages(models.Model):
transcript = models.ForeignKey(Transcript)
order = models.PositiveIntegerField('Order')
content = models.TextField('Page Content', null=True, blank=True)
The Admin behavior I’m trying to create is to let a user populate Transcript.body with the entire contents of a long document and, if they set Transcript.doPagination = True and save the Transcript admin, I will automatically split the body into n Transcript pages.
In the admin, TranscriptPages is a StackedInline of the Transcript Admin.
To do this I’m overridding Transcript’s save method:
def save(self):
if self.doPagination:
#do stuff
super(Transcript, self).save()
else:
super(Transcript, self).save()
The problem =
When Transcript.doPagination is True, I want to manually delete all of the TranscriptPages that reference this Transcript so I can then create them again from scratch.
So, I thought this would work:
#do stuff
TranscriptPages.objects.filter(transcript__id=self.id).delete()
super(Transcript, self).save()
but when I try I get this error:
Exception Type: ValidationError
Exception Value: [u'Select a valid
choice. That choice is not one of the
available choices.']
... and this is the last thing in the stack trace before the exception is raised:
.../django/forms/models.py in save_existing_objects
pk_value = form.fields[pk_name].clean(raw_pk_value)
Other attempts to fix:
t =
self.transcriptpages_set.all().delete()
(where self = Transcript from the
save() method)
looping over t (above) and deleting each item individually
making a post_save signal on TranscriptPages that calls the delete method
Any ideas? How does the Admin do it?
UPDATE: Every once in a while as I'm playing around with the code I can get a different error (below), but then it just goes away and I can't replicate it again... until the next random time.
Exception Type:
MultiValueDictKeyError Exception
Value: "Key 'transcriptpages_set-0-id'
not found in "
Exception Location:
.../django/utils/datastructures.py in
getitem, line 203
and the last lines from the trace:
.../django/forms/models.py in _construct_form
form = super(BaseInlineFormSet, self)._construct_form(i, **kwargs)
.../django/utils/datastructures.py in getitem
pk = self.data[pk_key]
