Is there a way to have shorter `_cls` values in mongoengine? - optimization

Question

Is there a way to have shorter _cls values in mongoengine, apart from making the names of the classes shorter (which would make code difficult to read)?
I was looking for something like this:
class User(Document):
login = StringField(primary_key = True)
full_name = StringField()
meta = { "short_class_name": "u" }
class StackOverFlowUser(User):
rep = IntField()
meta = { "short_class_name": "s" }
If the short_class_name meta attribute existed (but I have not found it or anything similar), then we could have this:
{ "_cls" : "s", "_id" : "john",
"full_name" : "John Smith", "rep" : 600 }
instead of this:
{ "_cls" : "User.StackOverFlowUser", "_id" : "john",
"full_name" : "John Smith", "rep" : 600 }
In this example, this leads to about 20% space saving, and in some cases, it could be even greater.
I guess mongoengine is open source, I could go ahead and code this, but if you know a simpler solution, I would love to hear it.
Thanks.

Answer 1

After looked into mongoengine's source code I and in most part MiniQuark got next hack:
def hack_document_cls_name(cls, new_name):
cls._class_name = new_name
from mongoengine.base import _document_registry
_document_registry[new_name] = cls
or as class decorator:
def hack_document_cls_name(new_name):
def wrapper(cls):
cls._class_name = new_name
from mongoengine.base import _document_registry
_document_registry[new_name] = cls
return cls
return wrapper
We see no other way than hacking with the _class_name and the _document_registry.
When you want to rename a class, you must apply this hack immediately after the class definition (or at least before you define any sub-classes, or else they will have a _types attribute with the base class's long name). For example:
class User(Document):
login = StringField(primary_key = True)
full_name = StringField()
hack_document_cls_name(User, "u")
class StackOverflowUser(User):
rep = IntField()
hack_document_cls_name(StackOverflowUser, "s")
or as class decorator:
#hack_document_cls_name("u")
class User(Document):
login = StringField(primary_key = True)
full_name = StringField()
#hack_document_cls_name("s")
class StackOverflowUser(User):
rep = IntField()

Answer 2

Ok, so far, the best I could come up with is this. It works, but I'm sure there must be less hackish solutions...
class U(Document): # User
meta = { "collection": "user" }
login = StringField(primary_key = True)
full_name = StringField()
class S(U): # StackOverflowUser
rep = IntField()
User = U; del(U)
StackOverflowUser = S; del(S)
User.__name__ = "User"
StackOverflowUser.__name__ = "StackOverflowUser"
Now when I do this:
StackOverflowUser.objects.create(login="john", full_name="John Smith", rep=600)
I get this document in the user collection:
{ "_cls" : "U.S", "_id" : "john", "full_name" : "John Smith", "rep" : 600 }
Compared to the standard behavior, this is about 20% space saving. But I don't like how hackish it is.