the best practice for DateTimeField default value initialization

[Ryutlis]

Hi,

I don't know if you guys noticed, the given demo code ( http://mongoengine-odm.readthedocs.org/en/latest/guide/defining-documents.html#defining-a-document-s-schema ) is not showing the right way to initialize DataTimeField with default value.

Because datetime.now() is executed when initializing the "class" body, so once the class is created, all instances will get the same default "time" which is wrong.

What I can think of the best practice, is to add a method explicitly do this job, for instance:

@classmethod

def add(cls, attr1, attr2, attr3):

    obj = cls(attr1=attr1, attr2=attr2, attr3=attr3, time=datetime.now())

    obj.save()

    return obj

What's your take on this?

--

@ryutlis

[Russ Weeks]

Hi, Ryutlis,

Note that there's no brackets () after "default=datetime.datetime.now" in the demo code.  What's happening is that the callable object datetime.now is being passed in as the default value.  Mongoengine is smart enough to recognize this as a callable and use its return value as the default value for the datetime field.  The callable will be evaluated at a different time for each object, producing the expected result.

Regards,

-Russ

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[Ryutlis Wang]

Ah.....

My fault... I didn't notice that...

Thank you, Russ, for clearing this up!