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<v Instructor>In this video,</v>

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we're gonna be building a handler factory function

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in order to delete review documents,

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but also documents from all the other collections,

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all with one simple function.

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So, as I mentioned right at the beginning of this section,

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adding very similar handlers to all of our controllers

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will create a lot of duplicate code, right?

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Because all these update handlers,

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or all these delete handlers,

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or all these create handlers,

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they really all just look basically the same, right?

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Also, imagine that we wanted to change

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like some https status code or status message.

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Then we would have to go into each and every controller

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and then change all the handlers in there.

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And so, instead of manually writing all these handlers,

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why not simply create a factory function

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that's gonna return these handlers for us?

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So, a factory function is exactly that.

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It's a function that returns another function,

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and in this case our handler function.

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So, for deleting, for creating, for updating,

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and also for reading resources.

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Okay and I know that this whole concept can be a bit complex

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to wrap your head around,

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and that's the reason why I left this

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for the later part of this course.

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But now, I believe that you're actually ready

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to implement this kinda stuff.

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So this kind of logic is what every advanced

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JavaScript developer should be able to implement,

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and so again I believe that at this point in the course

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you're really ready to start using advanced concept

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like this, all right.

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But enough talk, let me now show you how it actually works

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by using the delete handler as a first example.

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And so actually we have one in the tour controller,

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and so let's go ahead and copy that one,

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so delete tour.

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Okay, so I copied it basically

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as a template for us to follow.

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So let's create a new file, and I'm going to do that

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in the controllers.

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All right,

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so handler...

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factory.js.

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And I'm doing this is the controllers folder,

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well because the functions that we're gonna write here

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will basically return controllers.

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And so for me it makes a lot of sense

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that you put them here.

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So let's just copy this part here,

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just to keep it as a reference.

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So again the goal here is to basically create a function,

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which will then return a function

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that looks like this one here.

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But of course not only for the tour,

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but for every single model that we have in our application

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and that we might have in the future.

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So this function needs to be prepared for that,

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and so what that means is that inside the factory function,

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we will pass in the model, all right.

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So let's call this one deleteOne.

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And it's called like this, again,

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because this function is not only going

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to work to delete tours,

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but also to delete reviews and users

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and in the future some other documents

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that we might also have.

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So as I was saying in the beginning,

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we will pass the model into this function.

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So we pass the model and then we create a new function,

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and that function will right away

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then return our async function,

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so basically all of this or async handler function.

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Okay, and so now all we need to do is to actually change

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from the specific tool model to the more generic model.

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Then here we will also change this from tour to the document

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because again, we will not know what kinda document is this.

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So this function will not really know if it is a tour,

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or if it is a review, or a user.

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And so we need to take the tour out of all of this,

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and that's actually it.

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So this basically the generalization

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of this specific function, which worked only for tours,

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and now this new one works for every model.

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What we also need to do here is to import this catchAsync

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and also this AppError.

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So catchAsync...

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and I believe it's in the utilities folder.

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And then, not AppError but catchAsync.

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Then duplicate this here,

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AppError, and this here is uppercase.

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Give it a save, and we're now ready

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to actually test this out.

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So this is how it's going to work,

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first of all we need to import that handler factory.

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And so let's say,

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and I'm simply going to call it factory here.

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So require, and it's in the same folder,

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so handler factory.

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All right and so let's comment this one here out,

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or actually not all of this.

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Yeah or actually we can comment it out,

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and so the new exports.deletes tour will be...

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factory.deleteOne and then pass in the model,

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which is tour.

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And that's it, that's all we need to do.

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So just to recap very quickly here,

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so we call this deleteOne function,

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then in there we pass the model,

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and so what's going to happen is that this function

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will then right away return this handler function

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that we had before.

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Simply the specific model, which before was the tour,

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is now going to be replaced with the one

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that we passed into the function.

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And by the way this works because of JavaScript closures,

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which is just a fancy way of saying

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that this inner function here will get access

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to the variables of the outer function

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even after the outer has already returned.

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So calling this function here

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will then return another function,

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which will then sit here and wait until it is finally called

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as soon as we hit the corresponding route.

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And so let's now try exactly that.

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So delete tour,

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okay, and let's choose a tour

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that we don't really need here for now.

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So let's say...

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now let's say here The Snow Adventurer

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'cause it also doesn't have any reviews.

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So let's send that,

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oh and now we don't have permission to preform the action,

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and that's because we're not logged in as an admin.

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So let's try that,

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and so this is the admin that we need to be logged in.

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Okay, so that's done.

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And so now this should work, and indeed it did work.

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And so that's proof that our factory function

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is really doing it's job.

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Okay 'cause if you now come back here,

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we had 10 results and so now we should only get nine,

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so perfect.

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And now the goal is to be able to use this

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in each and every single controller.

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So let's copy this here

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and go to the reviews.

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Oh and of course we need it up here,

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right in the beginning, now right,

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and so now export.deleteReview

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is equal to factory.deleteOne

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with the review model.

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And that's it, that's all we need to do

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in order to implement the delete handler.

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Now of course we also need to specify the route handler.

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Now of course we need to specify the route itself,

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and so let's do that here as well.

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So router.route

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because here we actually need the ID parameter.

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And now delete is simply reviewController.deleteReview,

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and I'm not messing with the permission here,

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neither with authentication

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because for now I just want to make this work

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and worry about that stuff a bit later in this section.

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Okay, so let's close this stuff up here.

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So get all reviews,

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all right,

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let's save this and this one as well.

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So that now we can start with a blank sheet here

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and let's just start by getting all reviews,

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so that we can now delete one.

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And so let's delete, well just this one.

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Okay, now we also need of course this,

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and then the delete http method.

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We need no authorization at this point,

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so let's just send it.

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And indeed no content, so 204.

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And if we now get all the reviews,

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then we should be back to having just three.

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Yep, that works and so let's move on to the next one.

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Okay so reviews, reviews.

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Let's get this line of code here and now finally add it

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to the user controller as well.

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All right, and of course all of this,

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I understand it's a bit confusing now messing

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with all of these different files,

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but we just need to do it once and then we're done

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with all that confusion.

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So here we already had the export.deleteUser,

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now all we need to do is to then call our factory function,

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so deleteOne and then the user.

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Now only the administrator should later be able

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to actually delete users because remember that

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when the user deletes himself,

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then they will not actually get deleted

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but only active will be set to false.

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But the administrator on the other hand

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is really gonna be able to delete the user effectively

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from the database.

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But again, we're going to worry

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about that permission stuff a bit later.

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For now, let's check in the userRoutes

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if the route is actually implemented,

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and yeah it is down here.

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And so since we now implemented this,

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let's also test it here again also on Postman.

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So first let's save this one.

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So...

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delete review,

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and now let's simply copy this

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into yet another route.

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So delete and then one user,

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but I'm actually not really going to do it now.

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All I want is to just get some random ID.

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Or actually let's just create a new user,

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so basically sign up, and then delete that one right away.

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So hello, like this.

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Get all users, and then it's this guy here.

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And so let's delete him right away,

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so we send, we get 204 no content.

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And of course, now he should be gone.

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Now if we try to see her again,

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so basically trying to delete a user

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that is no longer there, we should get an error.

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So let's take a look, and indeed no document found

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with that ID.

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And so this means that in our factory function,

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so right here, all of this the AppError and the catchAsync,

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all of that is still intact.

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So everything still works just the same as before.

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Now so that was also important to test here.

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Let's just quickly save this here as well,

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so each and every single endpoint that we're implementing,

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I'm also adding it here into Postman

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because a bit later we will then actually be able

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to actually create some API documentation

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based on all of this that we have saved here in Postman.

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So that's yet another handy feature of this application.

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So we have delete the current user,

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and again that's different from just deleting the user

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because this one here is for administration

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and this one is for the currently logged in user,

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so very different.

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Okay, so this was our first factory function

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only for deleting and only for you to understand

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the concept itself.

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Next up, we're then gonna implement factory functions

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for updating and for creating documents.