I'm finding it difficult to denormalise a field in a django model. I
have:
class AnswerSet(models.Model):
title = models.CharField(max_length=255)
num_answers = models.PositiveIntegerField(editable=False,
default=0)
answers = models.ManyToManyField(Answer,
through='AnswerSetAnswer')
...
class AnswerSetAnswer(models.Model):
answer = models.ForeignKey(Answer)
answer_set = models.ForeignKey(AnswerSet)
...
I want num_answers to contain a count of the number of answers in the
set.
If 5 answers are initially associated with the AnswerSet "Food" and I
edit one so it becomes associated with the AnswerSet "Colours", how
can I recalculate the number of answers in the AnswerSet with "Food"?
All the signals only seem to send the new data so I can't just
override the save method.
I've tried using the m2m_changed signal, but it never gets called when
I edit relationships through the admin form.
Here's my code anyway:
def update_answer_set_num_answers(sender, **kwargs):
"""
Updates the num_answers field to reflect the number of answers
associated with this AnswerSet
"""
print "hello" #
never gets here
instance = kwargs.get('instance', False)
print "no instance"
if not instance:
return
action = kwargs.get('action')
print "action: ", action
if (action != 'pre_remove' and action != 'pre_add' and action !
= 'clear'):
return
reverse = kwargs.get('reverse')
if reverse:
answer_set = instance.answer_set
else:
answer_set = instance.answer_set
num_answers =
AnswerSetAnswer.objects.filter(answer_set=answer_set.id).count()
if (action == 'pre_remove'):
num_answers -= int(kwargs.get('pk_set'))
elif (action == 'pre_add'):
num_answers += int(kwargs.get('pk_set'))
elif (action == 'clear'):
num_answers = 0
answer_set.num_answers = num_answers
print 'n a: ', answer_set.num_answers
answer_set.save()
m2m_changed.connect(update_answer_set_num_answers, \
AnswerSet.answers.through)
Setting weak=False or weak=True makes no difference.
How can I get the signal to work?
Thanks
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