what's the purpose of line_allocated_event for redis? #70

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1. uguryiilmz commented on May 12, 2023

   

   uguryiilmz

   on May 12, 2023

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   upon investigating more, i noticed everything is working as expected. Book was right about event driven systems being more difficult to understand the flow. So if anyone else is having a problem understanding what's going on, here's the explanation:

   1. creating a subscription on "line_allocated_channel", in which this channel is only triggered if reallocation happens

   2. publishing a message on 'change_batch_quantity' channel, so this part is important because when a new message is published to this topic/channel, it'll trigger change_batch_quantity() command method from product domain. Once this happens, it will also add new events to our event list with this line
      self.events.append(events.Deallocated(line.orderid, line.sku, line.qty))

   3. as long as we have events to process, unit of works will just pop them out and we will their own handler to process those events. Deallocated event's handler is reallocate function in the service layer's handle, which will in turn add another event to our queue which is commands.Allocate()

   4. now we have commands.allocate remaining in our events list, which calls allocate function again and then that adds new event to events queue. Then, this method is calling the handler from events services which is publish_allocated_events. This will be what we read from our subscription

   def publish_allocated_event(
       event: events.Allocated,
       uow: unit_of_work.AbstractUnitOfWork,
   ):
       logging.info("event is",event)
       print("event is",event)
       redis_eventpublisher.publish("line_allocated", event)
   
   

   it looks a little complicated but this is the whole workflow for the end-to-end test. Of course the tests can be expanded to also tests what messages is published into channel 'change_batch_quantity' to see the flow in more details