A '_type' field that can be used to automatically case documents

gistfile1.py

from mongokit import *
import numpy as np

class MongoMatrix(Document):
    structure = {}
    
    use_autorefs = True
    use_dot_notation=True
    atomic_save = True

class Test(MongoMatrix):
    structure = {'new':unicode}

class Run(Document):
    structure = {'title':unicode, 
                         'result': MongoMatrix, }
    
    use_autorefs = True
    use_dot_notation=True
    atomic_save = True

connection = Connection()

connection.register([Run, MongoMatrix, Test])

run = connection.test.example.Run()
test1 = connection.test.example.Test()
test1.new=u'we'
test1.save()
run.result = test1
run.save()
#The first save above will convert run.result into its base class
#When you save it again, the run.result base class is called and
#verification fails with:
#structureError: unknown fields : [u'new']
run.save()