Django DateTimeField auto_now_add 不起作用
在其中一个模型中，我设置了一个时间戳字段，如下所示：
created_datetime = models.DateTimeField(auto_now_add = True)
在 shell 中，我可以创建一个 obj 并保存它，但是在我的应用程序中，它引发了一个异常，created_datetime 字段不能为空。
很困惑哪里出了问题！！如何重新爱它。
In one of the model i have set one timestamp field as follows:
created_datetime = models.DateTimeField(auto_now_add = True)
While in shell i am able to create a obj and save it, however in my application it is raising a exception that created_datetime field cannot be null.
Confused where things went wrong!! How to reslove it.
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据我所知，默认日期时间的最佳实践是使用以下内容：
不要忘记导入日期时间
As far as I know, best practice for default datetimes is to use the following:
Don't forget to import datetime
我有这个，它真的让我困惑了很长时间。
事实证明，我的模型有一个自定义主键，这是由于在构造一些测试对象时未设置它的错误所致。
第一次，当
auto_now_add设置created_at时，效果很好。第二次没有，因为主键为空的对象已经存在，所以它正在进行更新。它尝试将其设置为created_atnull，这在我的模型中是不允许的。因此，值得检查一下您是否最终遇到此问题并出现错误“在我的应用程序中引发了一个异常，created_datetime 字段不能为空”，这可能是由于未正确设置主键造成的。
解决方案是我正确设置主键。
I had this and it really confused me for ages.
Turned out that my model had a custom primary key, and it was due to a bug not setting it when constructing some test objects.
The first time this worked fine as
auto_now_addsetcreated_at. The second time it didn't as the object with a null primary key already existed, so it was doing an update. And it tried to set that tocreated_atnull, which wasn't allowed in my model.So worth checking if you end up on this question with the error "in my application it is raising a exception that created_datetime field cannot be null", that that could be caused by not setting a primary key correctly.
The solution was for me to correctly set a primary key.
你可以做这样的事情
You can do something like this
这意味着从数据库中调用旧保存的created_at数据，并在
更新期间再次重新保存created_at 字段不起作用，因此静态保存，无需动态保存。
我的模型是
created_at = models.DateTimeField(auto_now_add=True)It means call your old saved created_at data from database and re-save again during
Updationcreated_at fields not working so save it statically, no need to do dynamically.
My model is
created_at = models.DateTimeField(auto_now_add=True)以下方式位于django文档的“part1”中
The following way is in the "part1" of django documentation