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All right my friends in this video we're going to take care of our last listener inside of the ticket

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service.

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So the order service at some point time is going to emit the order canceled events as soon as the ticket

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service sees that that is assigned to say that a given ticket is no longer reserved.

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So we're going to want to find a ticket inside of our tickets collection and remove the order idea property

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and say hey no longer is this ticket reserved.

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We can now make changes to it once again putting this listener together is going to be pretty easy and

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straightforward.

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It's going to be just about a total clone of the listener.

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We just wrote.

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So let's get to it right away.

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So back inside my ticket service of the listeners directory and inside there I'll make a new file of

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order canceled.

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Listener T.S.

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then at the very top.

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Once again we will get our listener base class and our order canceled event from our common module

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then export a class of order canceled listener.

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And that's going to be extending the listener base class and the generic type is going to be order canceled.

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Listener not worry cancel listener hurry cancel event.

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These terms really blend together at a certain point in time.

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That is why typescript is so fantastic here.

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It helps us catch those silly little typos.

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All right.

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So once again touch you it's going to tell us God.

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Define on message.

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Q Your name and subject let's take care a subject first.

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We'll get our subjects now from the com module our subject that we're going to listen for is the order

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or subject Scott order canceled and we'll sign the actual value of subject stock order canceled.

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Next up is our Q group name.

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Remember we had the separate file for that so we will import Q Group name at the top from Q Group name

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and then assign Q Group Name is Q Group name and then finally our async on message function that is

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going to take some data argument that is of type order canceled event at data and some message as well.

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And the message is coming from the no doubt streaming library so let's import that type at the very

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top.

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Okay.

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So inside of here as I mentioned just about identical logic to a listener we just put together of Order

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creator listener.

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We want to once again find a ticket if we can't find a ticket throw in there or then going to unset

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the order ideas property save the ticket publishing event saying that a ticket has been updated act

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the message and that's it.

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There should be pretty straightforward in order to find the ticket itself.

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We are going to import ticket from up to directories models ticket

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then down inside of on a message we'll make a new variable of ticket and I will come from a weight ticket

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dot and how we can actually find the ticket right here.

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Remember in the past it's been a really easy time finding all the relevant tickets because we could

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use find by idea or something similar.

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But we need to just keep in mind what information we actually have access to inside of this event.

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So to get a reminder of what information we have access to.

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We'll do a command click on order canceled event and that will tell us that we've got access to the

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orders I.D. we've got access to the order's version and we've also got access to the I.D. of the ticket

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that this order had reserved.

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That's how we can find the ticket inside of our tickets collection we'll reference data ticket dot I.D.

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So back over here we're going to run a ticket dot find by I.D. data that ticket dot I.D. that should

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find us the relevant ticket

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okay.

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So then after that we'll say that if we fail to find this ticket.

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So if there is no ticket then once again let's throw a new air now we'll just say something like I don't

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know.

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They get not found simple enough.

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Then after that we will make our update.

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We'll do a ticket set of the order ideas property and we want to clear this out.

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We want to say ticket not reserved anymore.

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You're going to change it back over to undefined

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we could potentially also put in NOLA right here.

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But you might recall it there are a couple of locations where we are doing kind of an existence check

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with typescript by using a question mark or an if statement or something similar that optional value

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optional values with typescript don't work terribly well with no.

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And so instead we are just gonna simply use undefined well then do it in a wait take it out save after

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that we will then publish an event saying that this ticket has been updated so backup at the top will

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once again get my ticket updated.

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Publisher from up one directory publishers ticket updated publisher

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then right after the save will do and await new ticket updated publisher.

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I'll pass in this client.

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We've been over that quite a bit now.

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We'll publish and events and once again we're gonna throw in a whole bunch of information from the ticket

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itself.

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So in total the idea of the ticket The New Order idea take care of that right away.

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That'll be a ticket order i.e. what else we've got our user I.D.

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our price our title and is that it.

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I feel like I'm missing of one property on this thing what is its version.

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There we go

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there we go.

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Very good and then finally at the bottom a message dot AK Like so s that should be at well this listener

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came together rather quickly and as I mentioned many times once we do something one time in the course

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hopefully all following times get a little bit faster so we should probably write out a quick test or

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two just to make sure that this thing works.

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I know testing these listeners has been pretty darn repetitive.

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It's really just the same thing again and again.

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But we've also seen several times where those tests help us catch a lot of different errors as well.

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Specifically a lot of errors coming from TypeScript and whatnot but nonetheless it helps helped us catch

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those.

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So even though I know the tests are a little bit tedious I really do think they are absolutely worth

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it.

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They also have to help us capture and test out some kind of corner cases as well.

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So do a quick pause right here.

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Come back next video and we're gonna write out lightning quick a quick test around this listener.