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‫(Man) So in this lecture, you're gonna learn how to

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‫chain multiple middleware functions for the same route.

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‫So up until this point, whenever we wanted to define

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‫a middleware, we only ever passed one middleware function.

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‫So for example here, for handling this post request,

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‫well we only passed in this middleware function

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‫which is our createTour handler.

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‫Okay? And so that's the only function that is gonna

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‫be called whenever we get a post request.

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‫Right? But lets now say that we want to actually

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‫run multiple middleware functions.

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‫Now you might ask "Why would we want to do that?".

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‫Well we might, for example, run a middleware before

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‫createTour here to actually check the data that is

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‫coming in the body.

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‫Right? So a bit similar to what we had before.

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‫So we did this check ID middleware before in order to

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‫check if the ID is actually valid and doing so outside

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‫of the actual route handlers so that they are

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‫only concerned with getting, updating, or deleting

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‫a tour.

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‫Right? And so here, in this specific example with post, we

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‫might want to do the same thing.

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‫So as I said, we might want to check if request.buddy

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‫actually contains the data that we want for the tour.

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‫Okay? And so lets do that.

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‫And actually, I want you to first do it on your own.

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‫So this is kind of a challenge that I want you to complete

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‫in order to use the concepts that we've talked about

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‫so many times at this point and create your own

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‫middleware function.

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‫So let me just write it here as a comment.

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‫So I want you to create

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‫a checkBody middleware function

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‫and in there I want you to check

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‫if the body contains the name property for the tour name

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‫and the price property.

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‫All right? And if not, I want you to send back a

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‫four-hundred status code.

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‫If not, send back four-hundred, which stands for

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‫bad request.

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‫So basically, an invalid request from the client, which is

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‫in this case, trying to create a new tour without a name

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‫and without a price property.

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‫Okay! And that's actually it.

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‫And (laughs) actually not.

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‫So I also want you to add it to the post handler stack.

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‫Basically. Okay?

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‫So I want you to add it in here.

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‫And I will actually tell you how to do that

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‫because we didn't do it at this point.

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‫So its very easy. Lets say our function is called middleware

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‫and so what you have to do is to simply add that function

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‫here before the createTour handler that will

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‫ultimately create the tour. Okay?

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‫So this way when we have a post request for this route,

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‫it will then run this middleware first and only then

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‫the createTour.

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‫Okay? So that's how we chain two different middlewares.

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‫But now I want you to go ahead and uh create this middleware

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‫actually called checkBody.

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‫So pause the video now and please try to do it on your own.

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‫Okay! So I hope you were successful doing that and then you

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‫tested it and that everything works.

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‫So now let me go ahead and implement it in my way.

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‫So we have this error here but don't worry about it.

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‫Its because of this middleware that's not defined.

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‫And so let me do it here right after the checkID middleware.

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‫So exports.checkBody.

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‫We have to request response and next.

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‫And so its actually quite simple.

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‫So if there is no request.body.name,

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‫and I think that's the name but lets quickly go

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‫ahead and check that.

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‫So it is here is tour simple.

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‫Yeah, and indeed its called 'name'

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‫and the other one is 'price'.

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‫So if there is no request body name or

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‫no request body.price

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‫well, in this case, we will, just as before, return from

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‫this function and send back a response.

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‫So the status here is remember: four-hundred add then

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‫some 'json' where the status is fail.

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‫So that's always when we have a four-hundred code.

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‫Add then the message

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‫"Missing name

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‫or price".

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‫Okay? So price and name need to be there at the same time.

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‫So if either the price is not there or the name is not there

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‫then we already send this error message.

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‫Okay? But if everything is correct, well then we want

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‫to move on to the next middleware.

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‫And so that's what we say here.

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‫And then next middleware will of course be createTour.

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‫So this one.

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‫So, lets go ahead and then add it here.

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‫So tourController.checkBody.

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‫All right so now the error is gone and we should be able

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‫to test it now. So lets close the ones we're not interested

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‫in and create a new tour.

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‫So right now we have our body with the name, duration, and

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‫difficulty but there is no price.

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‫So we should now get our error. Right?

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‫So lets test that. Send. And indeed, we have 'Missing name

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‫or price' with our four-hundred bad request.

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‫Okay? And so lets analyze what happened here again.

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‫So our request hit this route here and it was a post

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‫request. And so, it then run this middleware function

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‫and from this function, we then send out this uh response

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‫saying that, uh, well the name or the price is missing.

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‫Okay? But if now add the price...

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‫...so it doesn't really matter what price,

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‫send it, well then everything works just fine

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‫and we get a 201 created.

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‫So what happened this time? Well, it checked for the body

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‫and this condition was not true and so it called the next

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‫middleware in the stack which is createTour.

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‫So it created a tour and sent back the result

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‫and like this, finished the request-response cycle.

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‫Right? So I hope that was a, uh, nice small challenge and

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‫we will be using this kind of logic here all the time

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‫where we chain multiple kind of handlers here for the

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‫same route. So for example here we could check if a

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‫certain user is logged in or if he has the privileges, so

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‫the access rights, to even write a new tour.

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‫Or really all kinds of stuff that we want to happen

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‫before the tour is actually created.

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‫Okay? And once again we do that because we want to take

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‫all the logic that is not really concerned with creating the

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‫new resource outside of that handler. So that that handler

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‫is only concerned really with the work

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‫that is supposed to do.