Django 如何检查模型是否正在创建或更新

Question

在不使用信号的情况下，在模型保存方法中是否可以检查模型是否正在创建或更新？如果是这样怎么办？

def save(self, force_insert=False, force_update=False, *args, **kwargs):
        """
        Override of save() method which is executed the same
        time the ``pre_save``-signal would be
        """

        models.Model.save(self, *args, **kwargs)

Answer 1

您可以检查主键是否已创建（即不是None）：

def save(self, force_insert=False, force_update=False, *args, **kwargs):

    if self.pk is None:
        # model is going to be created
    else:
        # model will be updated

    super(YourModelClass, self).save(*args, **kwargs)

注意：当您仅检查

if id:

时，如果

False

具有值

id

，它将被视为

0

。看看这个：

>>> id = 0
>>> if id:
...     print("ID is set to %s" % id)
... # no result, but the value is set!

>>> id = 1
>>> if id:
...     print("ID is set to %s" % id)
...
ID is set to 1

>>> id = 0
>>> if id is not None:
...     print("ID is set to %s" % id)
...
ID is set to 0

Answer 2

尝试这样，

def save(self, force_insert=False, force_update=False, *args, **kwargs):

   if self.id:
      # updated
   else:
      # inserted

   models.Model.save(self, *args, **kwargs)

Answer 3

根据 Django 文档执行此操作的另一种方法：

def save(self, force_insert=False, force_update=False, *args, **kwargs):
  is_create = self._state.adding

  if is_create:
    # Do create stuff
  else:
    # Do update stuff
  super().save(*args, **kwargs)