使用 post_save 而不是 pre_save 信号检测字段变化
Detect field change using post_save instead of pre_save signal
我需要在某个字段更改时执行一些操作。
由于此操作需要与已保存的对象一起使用,我不能像这样使用 pre_save
信号:
@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
是否可以为此使用 post_save
信号?
我想避免向该模型添加临时属性。
是的,您也可以使用 post_save。但是你应该记住信号是同步的
使用 post_save 信号,您将无法从数据库中检索以前的状态 - 但为什么要使用信号呢?
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)
您可能还想阅读此内容:https://lincolnloop.com/blog/django-anti-patterns-signals/
我需要在某个字段更改时执行一些操作。
由于此操作需要与已保存的对象一起使用,我不能像这样使用 pre_save
信号:
@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
是否可以为此使用 post_save
信号?
我想避免向该模型添加临时属性。
是的,您也可以使用 post_save。但是你应该记住信号是同步的
使用 post_save 信号,您将无法从数据库中检索以前的状态 - 但为什么要使用信号呢?
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)
您可能还想阅读此内容:https://lincolnloop.com/blog/django-anti-patterns-signals/