Schemaless Triggers Example: Simplified Asynchronous Billing

schemalass_triggers_example.py

# We instantiate a client for talking with the Schemaless instance.
schemaless_client = SchemalessClient(datastore='mezzanine')

# We register the bill_rider function for the BASE column.
@trigger(column='BASE')

def bill_rider(row_key):
   # row_key is the UUID of the trip    
   status = schemaless_client.get_cell_latest(row_key, 'STATUS')

   if status.is_completed:
       # This means we have already billed the rider.
       return

   # Otherwise we try to bill.

   # We fetch the base trip information from the BASE column
   trip_info = schemaless_client.get_cell_latest(row_key, 'BASE')  

   # We bill the the rider
   result = call_to_credit_card_processor_for_billing_trip(trip_info)

   if result != 'SUCCESS':
       # By raising an exception we let Schemaless triggers retry later
       raise CouldNotBillRider()

   # We billed the rider successfully and write it back to Mezzanine
   schemaless_client.put(row_key, status, body={'is_completed': True, 'result': result})