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We were just taking a look at options or two and we eventually said that the issue with this approach

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is that we are allowing our query service to have a very deep understanding of what this comment moderated

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event is.

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So to solve this we're going to have a comment moderated b instead processed by the comments service.

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Let me show you how this is going to work out OK.

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So in this diagram on the left hand side we've got our comment service and the query service the comment

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service is the service that is ultimately in charge of exactly what a comment is and knows all the very

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precise business rules all the business logic everything around what a comment is how to update it and

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how to deal with it in some way.

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And so it makes a lot of sense to have our comment service be the one that is responsible for some very

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precise very well calibrated way of updating a comment whenever the comment service updates a comment

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by handling one of these very specialized events.

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We're going to have it emit one single very generic event called simply comment updated whereas all

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the events on the left hand side meant that we wanted to update a common in some very specific way that

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come an updated event says hey there's a new comment right here or a new version of this comment.

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Don't worry about what the update was.

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Don't worry about trying to interpret it.

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Don't worry about trying to run some specialized business logic around it.

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Just take these updated attributes and store them if you need them.

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So we're gonna follow this pattern throughout all the services we've put together the service that is

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in charge of a basic resource will be in charge of these various specialized updates and any time those

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specialized updates occur that service will emit a very generic event update so let's take a look at

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what this is going to look like for the services we are talking about right now.

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So we're going to once again have a user submitted comment as soon as they do so we're going to have

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our comments service versus that event and notably you'll notice that it now knows the status of that

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comment as well.

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The comment service will then continue to emit a comment created event that will go to the event bus

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it will go off to our moderation service and to the query service as well.

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So we're going to still solve that issue we ran into earlier where the query service didn't really know

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that a comment was created.

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And so that was where we ran into issues with the user submitted comment and then refreshing the page

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were then going to make sure that the moderation service still processes that comment and moderates

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it in some way.

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So that's going to go off to our event bus and now it's only going to go over to the comments service

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the comment service will be the only thing that knows how to process this very specialized update to

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what a comment is.

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So in this case we'll change the status around pending to approved then because the comment Service

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just made a change to a comment a very specialized very domain specific change that will then you missed

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a comment.

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Updated event.

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So this is a very generic event.

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It just says Hey some attributes change.

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Don't worry about what changed.

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Don't worry about processing this in any way.

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Just use these attributes if you care about it at all that will go off to the event bus the event plus

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we'll send it off to the query service.

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And now the query service is going to say oh a comment was updated.

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I don't care how or why it was updated.

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I'm just going to take all the different properties out of that event and I'm going to use those as

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the basis for my new comment or for update this comment.

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We're not going to necessarily just change that status flag.

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We're just going to say take all those attributes and use them to update our existing comment.

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That's it.

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Now I know that this might seem a little bit challenging to understand this idea of having a domain

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specific event in a very generic event.

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Well you're going to see many examples of this on the later project.

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We work on as well.

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So don't worry you'll get a lot of experience with this over time.

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So that's what we're gonna do inside of our application.

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We are going to use option number three.

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We're going to end up introducing two events.

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One is going to be very specialized in nature that is going to be the comment moderated event.

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It's going to be process by comment service and then as soon as comment service updates that comment

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it's going to emit that generic event to say hey this comment was just updated.

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If you care about it great use it in some way.

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Now the upside to this approach is that the query service only needs to know about common updated even

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if we start to add in a billion different ways of exactly how we can precisely update a comment query

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service doesn't need to know that it just needs to know oh this comment was updated on is going to take

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these attributes and use them OK.

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So now we understand what we're going to do inside of our application.

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We'll take a quick pause right here and start to implement option or three in just a moment.