How to use the pony.orm.db_session function in pony

    @db_session
    def test_create(self):
        """Test create episode"""
        series = Series(name='test')
        episode = Episode(
            series=series,
            season=1,
            number=2,
            name='test',
        )
        commit()
        Episode.get().should.be.equal(episode)

    @db_session
    def test_delete_item(self):
        item = Item[self.item.id]
        assert_in(item, Item.select()[:])
        res = self.client.delete("/api/v1/items/{0}".format(self.item.id))
        assert_not_in(self.item, Item.select())

def setUp(self):
        db.create_tables()
        # create some items
        with db_session:
            self.person = Person(firstname="Steve", lastname="Loria")
            self.person2 = Person(firstname="Monty", lastname="Python")
            self.item = Item(name="Foo", person=self.person)
            self.item2 = Item(name="Bar")

    @db_session
    def test_canonicalize_tracker_state(self):
        ts = self.mds.TrackerState(url='http://tracker.tribler.org:80/announce/')
        self.assertEqual(self.mds.TrackerState.get(url='http://tracker.tribler.org/announce'), ts)

@orm.db_session
def _get_asset(file_path):
    """ Get the database record for an asset file """
    record = model.Image.get(file_path=file_path)
    fingerprint = ','.join((utils.file_fingerprint(file_path),
                            str(RENDITION_VERSION)))
    if not record or record.fingerprint != fingerprint:
        # Reindex the file
        LOGGER.info("Updating image %s -> %s", file_path, fingerprint)

        # compute the md5sum; from https://stackoverflow.com/a/3431838/318857
        md5 = hashlib.md5()
        md5.update(bytes(RENDITION_VERSION))
        with open(file_path, 'rb') as file:
            for chunk in iter(lambda: file.read(16384), b""):
                md5.update(chunk)

    @orm.db_session
    @tornado.web.authenticated
    def post(self):
        action = self.get_argument('action', None)
        if action != "read":
            return
        user_id = force_int(self.get_argument('user_id', 0), 0)
        current_user = self.current_user
        user = User.get(id=user_id)
        if not user:
            return self.send_error(404)
        message_box = current_user.get_message_box(user=user)
        if not message_box:
            return self.send_error(404)
        message_box.status = 1
        return self.send_success_result(msg="已读")

return
    if len(leaves) > 1 and not fail_fast:
        # Merge required
        questioner = InteractiveMigrationQuestioner()
        if questioner.ask_merge(leaves):
            # not tested?
            merge(graph=graph, leaves=leaves)
            show_migrations(fail_fast=True)
            return
        return
    leaf = leaves[0]
    migrations = leaf.forwards_list()
    names = [m.name for m in migrations]

    try:
        with orm.db_session:
            orm.exists(m for m in db.Migration)
    except orm.core.DatabaseError as ex:
        print('No Migration table. Please apply the initial migration.')
        return

    saved = orm.select((m.name, m.applied) for m in db.Migration if m.name in names).order_by(2)[:]
    if saved:
        saved, _ = zip(*saved)
    for name in saved:
        print('+ {}'.format(name))
    for name in names:
        if name in saved:
            continue
        print('  {}'.format(name))

    @classmethod
    @orm.db_session
    def send_notification(cls, user_id):
        logging.info("Notification send")
        if user_id not in cls.users:
            return
        user = User[user_id]
        if not user:
            return
        data = {
            "count": user.unread_notification_count,
        }
        wss = cls.users[user_id]
        for ws in wss:
            try:
                ws.send('notification', **data)
            except Exception, e:
                logging.error(e)

@db_session
def highscores(year=None, month=None, day=None, week=None):
    mode = "all_time"
    title = "All Time"
    subtitle = None
    dt, f = None, None

    today = datetime.datetime.utcnow().date()
    r = today  # dummy for filter lambdas

    # daily highscores
    if year and month and day:
        mode = "day"
        dt = datetime.date(year, month, day)
        f = lambda: r.start_time.date() == dt
        title = dt.strftime("%B %d, %Y")

    @db_session
    def user(self):
        return User[self.user_id]