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‫Let's now improve the nested

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‫route implementation that we coded in the last lecture.

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‫And for that,

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‫we're gonna use a special advanced express feature.

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‫So, as you remember, in the last video

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‫we implemented a simple nested post route,

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‫so just this one here.

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‫Right. And so this means that the review route

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‫is kind of within the tour route.

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‫And again, because reviews belong to tours in a sense.

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‫Right?

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‫And so this is a very common thing to do in Api design.

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‫Now, the problem with this implementation is that it is,

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‫of course, a bit messy.

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‫And that is because we put a route for creating a review

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‫in the tour router.

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‫Simply because a route starts with slash tour.

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‫So that's a bit confusing,

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‫and what's also confusing

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‫is that we have something very similar to this here,

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‫also in our review route.

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‫So, basically this here.

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‫So when we create a new review without the nested route,

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‫this piece of the code here is actually exactly the same

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‫as this one. Right?

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‫And so, besides this being a bit confusing,

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‫we also have duplicate code which we would have to maintain

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‫in two separate places in case we wanted to change anything.

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‫And so again, that's a very bad practice.

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‫And so let's now fix this using an advanced express feature

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‫called mergeParams.

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‫So first off let's remove this code here

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‫which doesn't really belong to the tour router.

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‫Next up, we will actually import the review router

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‫into this tour router.

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‫Okay?

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‫So right now we are importing the review controller,

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‫but actually we want the review router.

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‫So let's get rid of this one,

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‫and actually I'm going to delete it altogether.

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‫And now,

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‫the review

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‫router.

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‫And okay.

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‫So, let's actually get this code

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‫and put it here at the top,

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‫just so that we see what we're doing,

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‫because we will actually create some new code

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‫right here at the top.

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‫And so what we're gonna do here

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‫is to say

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‫router.use.

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‫And so we will basically say that this tour router

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‫should use the review router

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‫in case it ever encounters a route like this.

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‫And

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‫Review routes.

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‫Did I call it routes or router?

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‫Should be called router.

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‫Okay?

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‫So, keep in mind that a router itself

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‫is really just a middleware.

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‫And so we can use the use method on it,

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‫and then say that for this specific route here,

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‫we want to use the review router instead.

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‫Okay?

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‫And so this is actually again mounting a router.

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‫So, if you take a look at that,

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‫here in the app.js,

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‫that's actually exactly what we did.

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‫So we did .use,

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‫then the URL,

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‫and then the router.

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‫And so here, what we're doing

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‫is actually the exact same thing.

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‫So this is the tour router, and so then we say

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‫well whenever you find a URL like this,

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‫well, then just use the review router.

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‫And so, right now, when we have a URL like this,

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‫it will start by getting into the tour router here,

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‫okay, because, again it starts with slash tours,

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‫okay,

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‫so basically it's rerouted into the tour router,

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‫then when it reaches the tour router,

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‫then it will match this URL here,

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‫and then it will again be rerouted into the review router.

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‫And like this, we have the tour router

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‫and the review router nicely separated

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‫and decoupled from one another.

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‫But now, there's actually still one piece missing

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‫because right now this review router here

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‫doesn't get access to this tour id parameter, okay.

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‫And so now we need to enable the review router

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‫to actually get access to this parameter here as well.

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‫So let's now move to the review router, okay.

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‫And so this is where the medical mergeParams

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‫that I mentioned right in the beginning

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‫comes into play.

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‫So here, in the express.router function,

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‫we can specify some options,

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‫and here all we need to do is set mergeParams

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‫to true.

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‫And that's it.

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‫But why do we actually need this here?

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‫Well, it's because, by default,

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‫each router only have access

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‫to the parameters of their specific routes, right.

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‫But here, in this route, so in this URL for this post,

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‫there's of course actually no tour id.

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‫But, we still want to get access to the tour id

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‫that was in this other router, right.

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‫So this here.

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‫And so, in order to get access to that parameter

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‫in this other router,

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‫we need to physically merge the parameters, okay.

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‫And so that's what mergeParams, set to true, does.

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‫And so now, no matter if we get a route like this,

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‫so let's just copy it here,

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‫Again it's easier to visualize it with an example.

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‫And so again, no matter if we get a route like this,

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‫or a route like this,

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‫it will now all end up in this handler here, okay.

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‫So in the end basically to this handler function.

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‫And again that works because all of the routes

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‫starting with this kind of pattern here

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‫will be redirected to this router

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‫exactly in this line of code here, okay.

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‫So we redirected to the review router here

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‫and so then in there it will match to this exact route,

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‫okay.

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‫And thanks to merge parameters,

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‫we then get access to this id

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‫which actually comes from the other router before.

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‫Great.

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‫So let's just do some clean up here,

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‫actually get rid of this,

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‫this here,

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‫and

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‫let's quickly try it out now.

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‫So I'm gonna create a new review here

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‫and let's try another tool this time.

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‫So the city wanderer.

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‫And all we need to do is to change

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‫that id right here in the URL, right.

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‫So, the rating is gonna be three,

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‫and then

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‫was kinda okay.

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‫All right, and so this review will still be done with Jonas,

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‫so from this account, okay,

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‫because that's still one

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‫that is logged in at this current moment, okay.

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‫So, let's send that,

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‫and indeed here we get the tour that we just specified,

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‫and still the same user.

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‫So that's again just to make sure check the tour

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‫to see if it now gets this review

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‫and yeah, it did.

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‫And so that merge parameter trick, that we just implemented,

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‫actually works just fine,

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‫and as intended.

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‫Now to see this in action, even better,

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‫we're gonna adapt the henry function

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‫for getting all the reviews for a specific tour

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‫right in the next video.