def get_latest_orderbook_for_exchange(self, gds_db, exchange):
orderbook = None
if self.no_lookback_limit is True:
orderbook = gds_db.query(Orderbook)\
.filter(Orderbook.exchange == exchange.name.upper())\
.order_by(Orderbook.timestamp.desc())\
.first()
else:
# We only show orderbooks from the last hour.
now = Delorean()
latest_orderbook_time = now.naive
earliest_orderbook_time = now.last_hour(1).naive
orderbook = gds_db.query(Orderbook)\
.filter(Orderbook.exchange == exchange.name.upper())\
.filter(Orderbook.timestamp > earliest_orderbook_time)\
.filter(Orderbook.timestamp <= latest_orderbook_time)\
.order_by(Orderbook.timestamp.desc())\
.first()
return orderbook
