'modified: removing the \'_cls\' column added by Mongoengine to support mongodb document inheritance
cf. http://docs.mongoengine.org/apireference.html#documents:
"A Document subclass may be itself subclassed, to create a specialised version of the document that will be
stored in the same collection. To facilitate this behaviour a _cls field is added to documents (hidden though
the MongoEngine interface). To disable this behaviour and remove the dependence on the presence of _cls set
allow_inheritance to False in the meta dictionary."'

def get_columns_list(self):

    columns = list(self.obj._fields.keys())
    if ('_cls' in columns):
        columns.remove('_cls')
    return columns
