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我发现很难在django模型中规范化字段。我有:django中的非规范化字段
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)
...
我希望num_answers包含集合中答案的数量。
如果5个答案最初与AnswerSet“Food”相关联,并且我编辑了一个答案以便它与AnswerSet“Colors”相关联,那么如何重新计算AnswerSet中含有“Food”的答案数?所有的信号似乎只发送新的数据,所以我不能只是重写保存方法。
我试过使用m2m_changed信号,但是当我通过管理窗体编辑关系时,它永远不会被调用。
这里是我的代码吗:
def update_answer_set_num_answers(sender, **kwargs):
"""
Updates the num_answers field to reflect the number of answers
associated with this AnswerSet
"""
instance = kwargs.get('instance', False)
print "no instance" # never gets here
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, weak=False)
是的,它会很方便。例如,我想要显示5个随机答案集,它们都有3个答案。我希望有很多答案集,这将有助于扩大规模 – Roger 2010-09-13 20:47:12