Update counters per day and hostname with transactions in Google NDB

models.py

from google.appengine.ext import ndb
from datetime import datetime, timedelta, date

#
#
#

class HostConnection(ndb.Model):
    date = ndb.DateProperty()
    host = ndb.StringProperty()
    connections = ndb.IntegerProperty(default=0)

    @classmethod
    @ndb.transactional()
    def update_count(cls, host, count):
        today = date.today()
        key_name = "{}:{}".format(today, host)
        entry = cls.get_by_id(key_name)
        if entry is None:
            entry = cls(id=key_name, date=today, host=host, connections=count)
        else:
            entry.connections += count

        entry.put()