Hi,
I've modeled a Book that has Chapters, with each Chapter having an ordering
'sequence'.
So when someone decides the first chapter in the book should become the
third, they can just change the sequence number.
That's fine, but when that happens, I want the other chapters to
automatically change their sequence to reflect the change.
To accomplish this I thought I could add a custom 'save' method to my
Chapter model, but I get the message:
'Manager isn't accessible via ChapterMembership instances'
My code seems straightforward enough:
class ChapterMembership(models.Model):
chapter = models.ForeignKey(Chapter, blank=True, null=True)
book = models.ForeignKey(Book, blank=True, null=True)
sequence = models.PositiveIntegerField()
def save(self):
chapters = self.objects.filter(book=self.book) # get all instances
for the related book
sequences = [x.sequence for x in chapters] # a list of all the
sequence numbers
if self.sequence in sequences: #if we have a duplicate sequence
take care of it
for chapter in chapters:
if self.sequence == chapter.sequence:
chapter.sequence = chapter.sequence + 1
chapter.save() # makes this a recursive method
super(ChapterMembership, self).save()
I suppose I'm missing something basic, but I haven't seen an example like
this in my searches.
Can anyone see what I'm doing wrong?
thanks,
--Tim
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