mongoengine Proposal: auto_now and auto_now_add options for DateTimeField

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There are two very useful options for DateTimeField in Django: auto_now and auto_now_add.

From django docs: """ auto_now Automatically set the field to now every time the object is saved. Useful for "last-modified" timestamps. Note that the current date is always used; it's not just a default value that you can override.

auto_now_add Automatically set the field to now when the object is first created. Useful for creation of timestamps. Note that the current date is always used; it's not just a default value that you can override. """

I think it is very simple task to implement auto_now_add behavior at least. I understand that implementing auto_now is a bit harder. By the way the fact that MongoEngine still has no support for these options lets me think that this is done by design. Which is not right by my personal opinion.

May 16 '12 12:05 lig

Well I'd suggest using signals, but it all depends on how you update your documents. Doing a save in pymongo will overwrite a document and isn't atomic. We do some handling of that, to make it atomic but there is a big cost in performance involved.

You can set a default which covers auto_now_add but auto_now is tricker to implement as it may be a mass update and arguably should be left to the application developer to implement.

May 16 '12 13:05 rozza

Well, I've just noticed once more callable defaults and see default=lambda: datetime.utcnow() variant. But may be it will be useful to have this out of the box.

And yes, I understand that implementing auto_now is a kind of scary task:)

Also, I think that documenting design principles for auto_now and auto_now_add and the reasons why there shouldn't be auto_now out of the box will be very useful.

May 16 '12 13:05 lig

I dont think its a scary task - should be relatively trivial, its just we'd have to hook into every save (easy) and inject into every update call - maybe unexpected for the user.

I'll schedule for post 0.7 - but it might make 0.7

May 16 '12 13:05 rozza

Thank you very much!

Now I may try to contribute some code on this task. Not promising that I will though.

May 16 '12 13:05 lig

Having to bump to 0.8 as PY3 support came early!

Aug 24 '12 09:08 rozza

damn... how do I deactivate this :))

Sep 03 '14 19:09 csabaszilveszter

So is this supported now? In which version? Thanks!

Jul 27 '15 21:07 beyondliu

Look at the following code snippet, it will clarify.

class Post(models.Model):
     title = models.CharField(max_length=50, blank=False)
     description = models.TextField()
     pic = models.URLField(max_length=1000) #default max_length is 200
     created = models.DateTimeField(auto_now_add=True, auto_now=False)
     updated = models.DateTimeField(auto_now_add=False, auto_now=True)
     posted_by = models.ForeignKey(User, on_delete=models.CASCADE) # "User" => won't work

     def __unicode__(self):
           return self.title