0

这是我的模型：

class MyModel(models.Model):
    timeStamp = models.DateTimeField(default=datetime.datetime.utcnow())
    def __unicode__(self):
        return "MyModel ID=%s at <%s %s>" % (
            self.id, 
            self.timeStamp.strftime("%H:%M:%S.000").rstrip("0").rstrip("."), 
            self.timeStamp.strftime("%m/%d/%Y")
        )

看看当我从控制台运行一些命令时会发生什么：

>>> from MyApp.models import *
>>> import datetime

>>> MyModel()
<MyModel: MyModel ID=None at <02:04:45 03/25/2014>>

>>> # Wait several seconds
>>> MyModel()
<MyModel: MyModel ID=None at <02:04:45 03/25/2014>>

>>> # Wait several seconds
>>> MyModel()
<MyModel: MyModel ID=None at <02:04:45 03/25/2014>>


>>> # Wait several seconds
>>> MyModel(timeStamp=datetime.datetime.utcnow())
<MyModel: MyModel ID=None at <02:07:16 03/25/2014>>

>>> # Wait several seconds
>>> MyModel()
<MyModel: MyModel ID=None at <02:04:45 03/25/2014>>

>>> # Wait several seconds
>>> MyModel()
<MyModel: MyModel ID=None at <02:04:45 03/25/2014>>

为什么 timeStamp 的默认值（应该为每个 MyModel 分配给 datetime.datetime.utcnow()）与我创建的第一个值保持不变？

如果我在构造函数中手动设置该值，它唯一会改变，这是一个丑陋的黑客！

看起来默认值正在被缓存并不断重复使用。如何防止这种缓存发生？

4

1 回答 1

1

因为你已经调用了它。而是将其作为函数传递。

timeStamp = models.DateTimeField(default=datetime.datetime.utcnow)
于 2014-03-25T02:36:07.407 回答