fix change tracking for ComplexBaseFields

[paulswartz]

No description provided.

[amcgregor]

What about:

class Foo(Document):
    bar = ListField(StringField(), default=list)

instance = Foo()
instance.bar.append('foo')
instance.save()
instance.bar.append('bar')
del instance.bar[1]

print(instance._changed_fields)

Technically not changed?

[paulswartz]

Technically no, but you'd have to store the original value somewhere and compare them, and that seems like a lot of extra work. This just lets the default behavior work, which doesn't mark the value as changed if it's the same as the current value.

[rozza]

@paulswartz thanks for the ticket - out of interest was this causing an issue for you? Marking for 0.8.2

[rozza]

@amcgregor the change tracking is very naive - I have scheduled for 0.9 to improve it - so you can do list operations without replacing the whole list.

[paulswartz]

@rozza I have a mixin which does model change tracking, and I noticed that I was getting spurious changes recorded.

[rozza]

@paulswartz sounds interesting anything that should be in mongoengine or mongoengine extras :D 👍

[paulswartz]

@rozza it's also pretty naive, but I'll make a note to look at breaking it out.

[rozza]

Thanks @paulswartz for the code 👍 good spot.