[英]Detect field change using post_save instead of pre_save signal
當一個字段更改時,我需要執行一些操作。
由於此操作需要處理已保存的對象,因此無法使用pre_save
信號,如下所示:
@receiver(pre_save, sender=reservation_models.Reservation)
def generate_possible_pairs(sender, instance, **kwargs):
try:
reservation_old = sender.objects.get(pk=instance.pk)
except sender.DoesNotExist:
pass # Object is new, so field hasn't technically changed, but you may want to do something else here.
else:
if not reservation_old.datetime == instance.datetime: # Field has changed
do_something(instance) # It would be better to be sure instance has been saved
是否可以為此使用post_save
信號?
我想避免向此模型添加臨時屬性。
使用post_save信號,您將無法從db檢索以前的狀態-但是為什么要使用信號呢?
class Reservation(models.Model):
def save(self, *args, **kw):
old = type(self).objects.get(pk=self.pk) if self.pk else None
super(Reservation, self).save(*args, **kw)
if old and old.datetime != self.datetime: # Field has changed
do_something(self)
您可能還需要閱讀以下內容: https : //lincolnloop.com/blog/django-anti-patterns-signals/
是的,您也可以使用post_save。 但是,您應該記住信號是同步的
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