1 00:00:01,050 --> 00:00:02,840 ‫Let's now make some more use 2 00:00:02,840 --> 00:00:04,780 ‫of our AppError class 3 00:00:04,780 --> 00:00:07,400 ‫business adding a couple of 404 errors 4 00:00:07,400 --> 00:00:09,493 ‫and some of our tour handler functions. 5 00:00:10,446 --> 00:00:12,740 ‫Now just one thing that I wanted to say 6 00:00:12,740 --> 00:00:16,030 ‫before we actually implement these 404 errors 7 00:00:16,030 --> 00:00:19,640 ‫is that of course we could have used the catchAsync function 8 00:00:19,640 --> 00:00:22,290 ‫also in our router, okay? 9 00:00:22,290 --> 00:00:24,940 ‫So, let me show you how that would work. 10 00:00:24,940 --> 00:00:27,090 ‫So, here in TourRoutes, 11 00:00:27,090 --> 00:00:29,730 ‫I could have wrapped this function here 12 00:00:30,750 --> 00:00:34,530 ‫into catchAsync just like this 13 00:00:34,530 --> 00:00:38,480 ‫instead of doing it right in here in the controller. 14 00:00:38,480 --> 00:00:41,400 ‫So, here where I did it in fact, right? 15 00:00:41,400 --> 00:00:44,200 ‫And that would have had the exact same result 16 00:00:44,200 --> 00:00:45,950 ‫but I didn't do it this way 17 00:00:45,950 --> 00:00:48,190 ‫because like this, I have to remember 18 00:00:48,190 --> 00:00:50,110 ‫which of these methods here 19 00:00:50,110 --> 00:00:52,350 ‫is actually an sync method, 20 00:00:52,350 --> 00:00:54,800 ‫okay, so that only on those 21 00:00:54,800 --> 00:00:58,960 ‫I actually add the catchAsync function, right? 22 00:00:58,960 --> 00:01:02,150 ‫Now in this case, actually all of them are async function 23 00:01:02,150 --> 00:01:05,700 ‫and so, that's not really the matter here in this example 24 00:01:05,700 --> 00:01:07,530 ‫but there will be some examples later 25 00:01:07,530 --> 00:01:11,150 ‫where not all the handlers are asynchronous functions 26 00:01:11,150 --> 00:01:12,170 ‫and so, in that case, 27 00:01:12,170 --> 00:01:14,020 ‫I would really have to remember 28 00:01:14,020 --> 00:01:17,100 ‫which of them I have to wrap into catchAsync 29 00:01:17,100 --> 00:01:18,600 ‫and which ones not 30 00:01:18,600 --> 00:01:20,450 ‫and so, in doing it in the controller 31 00:01:20,450 --> 00:01:23,930 ‫is much easier because simply each time that I'm writing 32 00:01:23,930 --> 00:01:25,520 ‫an async function here, 33 00:01:25,520 --> 00:01:27,190 ‫they already know well, 34 00:01:27,190 --> 00:01:30,220 ‫I need to wrap it into catchAsync. 35 00:01:30,220 --> 00:01:31,350 ‫Okay. 36 00:01:31,350 --> 00:01:32,880 ‫So, I'm not doing it here, 37 00:01:32,880 --> 00:01:36,400 ‫I just do it like I showed you in the last video. 38 00:01:36,400 --> 00:01:39,680 ‫Okay and actually I once run into a bug 39 00:01:39,680 --> 00:01:41,330 ‫that was really hard to find 40 00:01:41,330 --> 00:01:43,160 ‫because I actually wrapped a function 41 00:01:43,160 --> 00:01:45,690 ‫that was not async into catchAsync 42 00:01:45,690 --> 00:01:47,850 ‫and so that we really not working 43 00:01:47,850 --> 00:01:50,350 ‫and I couldn't figure out where the bug was 44 00:01:50,350 --> 00:01:52,830 ‫and wasted a lot of time on that one. 45 00:01:52,830 --> 00:01:56,820 ‫And so, since then, I no longer put catchAsync here 46 00:01:56,820 --> 00:01:59,610 ‫but really close to where I actually need it, 47 00:01:59,610 --> 00:02:02,860 ‫so close to the code that is actually asynchronous. 48 00:02:02,860 --> 00:02:04,640 ‫Okay and with that being said, 49 00:02:04,640 --> 00:02:07,820 ‫let's now implement some 404 errors here. 50 00:02:07,820 --> 00:02:09,680 ‫All right, so I wanna start 51 00:02:09,680 --> 00:02:11,680 ‫by showing you again the example 52 00:02:11,680 --> 00:02:13,830 ‫that we did in the last video. 53 00:02:13,830 --> 00:02:16,350 ‫Okay, so we tried to get a tour 54 00:02:16,350 --> 00:02:19,780 ‫for this weird ID that does not really exist 55 00:02:19,780 --> 00:02:20,989 ‫and the error that we got 56 00:02:20,989 --> 00:02:23,690 ‫is that basically Mongoose 57 00:02:23,690 --> 00:02:26,410 ‫could not convert this string here 58 00:02:26,410 --> 00:02:29,630 ‫into a valid ID for MongoDB. 59 00:02:29,630 --> 00:02:33,653 ‫But what happens when we actually use a valid MongoDB ID? 60 00:02:34,750 --> 00:02:38,003 ‫So, for example, let's, yeah, 61 00:02:38,003 --> 00:02:39,173 ‫let's copy this one here, 62 00:02:41,660 --> 00:02:44,670 ‫okay, and this one of course will have a result 63 00:02:44,670 --> 00:02:47,770 ‫and so, let's just slightly change it, 64 00:02:47,770 --> 00:02:50,060 ‫so for example, changing this to zero here 65 00:02:50,060 --> 00:02:52,340 ‫will still be a valid ID, 66 00:02:52,340 --> 00:02:53,900 ‫so it looks like this 67 00:02:53,900 --> 00:02:56,000 ‫and it looks exactly the same as before, 68 00:02:56,000 --> 00:02:57,440 ‫I just changed one number 69 00:02:57,440 --> 00:03:00,830 ‫but this ID will probably not exist. 70 00:03:00,830 --> 00:03:03,470 ‫And so, let's see what we get then. 71 00:03:03,470 --> 00:03:06,810 ‫And indeed, now our result here is null. 72 00:03:06,810 --> 00:03:10,340 ‫All right, and so, that's not really what we want, is it? 73 00:03:10,340 --> 00:03:14,550 ‫What we want here is to show a 404 status code in here 74 00:03:14,550 --> 00:03:17,310 ‫and say that this tour was not found. 75 00:03:17,310 --> 00:03:20,750 ‫Okay and so, let's now use orAppError class 76 00:03:20,750 --> 00:03:22,580 ‫in order to implement that. 77 00:03:22,580 --> 00:03:24,040 ‫Just keep in mind that the tour 78 00:03:24,040 --> 00:03:26,880 ‫that we get back here is null, okay? 79 00:03:26,880 --> 00:03:29,453 ‫So, null that we can now test for. 80 00:03:30,920 --> 00:03:33,533 ‫So, if we go to our getTour handler, 81 00:03:35,260 --> 00:03:40,260 ‫let's now implement if there is no tour 82 00:03:41,030 --> 00:03:43,390 ‫and in that case we will create or error 83 00:03:44,410 --> 00:03:45,243 ‫and this here works 84 00:03:45,243 --> 00:03:46,650 ‫because if there's no tour, 85 00:03:46,650 --> 00:03:47,710 ‫it will be null. 86 00:03:47,710 --> 00:03:51,610 ‫Remember and in JavaScript, null is a fallacy value, 87 00:03:51,610 --> 00:03:54,660 ‫so a value that will convert to false here 88 00:03:54,660 --> 00:03:56,250 ‫in an if statement. 89 00:03:56,250 --> 00:03:58,060 ‫Okay, and so, if there's no tour, 90 00:03:58,060 --> 00:03:59,450 ‫then tour is false 91 00:03:59,450 --> 00:04:01,790 ‫and then not false is of course true 92 00:04:01,790 --> 00:04:04,830 ‫and so, that's then how we enter this if block. 93 00:04:04,830 --> 00:04:07,600 ‫So, what do we want to do if there is no tour? 94 00:04:07,600 --> 00:04:11,530 ‫Well, we want to create next with an error. 95 00:04:11,530 --> 00:04:14,861 ‫So, in order to jump straight into or error 96 00:04:14,861 --> 00:04:15,990 ‫and linked middleware. 97 00:04:15,990 --> 00:04:18,870 ‫So, we do new AppError 98 00:04:20,610 --> 00:04:23,350 ‫which si not available yet, we still have to import it 99 00:04:23,350 --> 00:04:26,120 ‫but let's use it here right away. 100 00:04:26,120 --> 00:04:27,950 ‫Okay, and then let's just say 101 00:04:30,500 --> 00:04:34,673 ‫No tour found with that ID. 102 00:04:35,580 --> 00:04:37,070 ‫And then a status code remember 103 00:04:37,070 --> 00:04:40,940 ‫is the second argument is 404, all right? 104 00:04:40,940 --> 00:04:43,460 ‫Now one last thing that we need to do here 105 00:04:43,460 --> 00:04:46,470 ‫which is to say return, okay 106 00:04:46,470 --> 00:04:49,410 ‫because we want to return this function immediately 107 00:04:49,410 --> 00:04:52,250 ‫and not move on to the next line 108 00:04:52,250 --> 00:04:53,690 ‫which would be this one 109 00:04:53,690 --> 00:04:57,800 ‫and which would then basically try to send two responses 110 00:04:57,800 --> 00:05:00,210 ‫and we did already run into that error before, 111 00:05:00,210 --> 00:05:02,020 ‫so I'll hope you'll remember that 112 00:05:02,020 --> 00:05:05,580 ‫and that's the reason why we always need return here. 113 00:05:05,580 --> 00:05:09,610 ‫Okay, let's now go ahead and quickly import the appError 114 00:05:10,870 --> 00:05:13,200 ‫and that's similar to this one here, 115 00:05:13,200 --> 00:05:14,823 ‫so let's just duplicate. 116 00:05:17,990 --> 00:05:21,203 ‫Okay, and here it's actually with a capital A. 117 00:05:22,170 --> 00:05:24,210 ‫All right, give it a save 118 00:05:24,210 --> 00:05:25,850 ‫and let's now try it again 119 00:05:27,160 --> 00:05:31,450 ‫and now indeed no tour found with that ID 404. 120 00:05:31,450 --> 00:05:34,440 ‫Perfect, so exactly what we wanted. 121 00:05:34,440 --> 00:05:37,170 ‫Oh and you also saw that we have the failed here. 122 00:05:37,170 --> 00:05:40,980 ‫Okay and so that comes from or class as well. 123 00:05:40,980 --> 00:05:44,270 ‫Great, so that works and so I really hope 124 00:05:44,270 --> 00:05:48,060 ‫that by now you understood exactly how all 125 00:05:48,060 --> 00:05:50,370 ‫of this error handling now works. 126 00:05:50,370 --> 00:05:53,300 ‫Okay, so again we create an error 127 00:05:53,300 --> 00:05:55,450 ‫and we then pass that error into next 128 00:05:55,450 --> 00:05:57,820 ‫and as soon as next receives something, 129 00:05:57,820 --> 00:05:59,880 ‫it assumes that it is an error 130 00:05:59,880 --> 00:06:00,757 ‫and it will jump straight 131 00:06:00,757 --> 00:06:03,630 ‫into the global error handling middleware 132 00:06:03,630 --> 00:06:06,683 ‫which will then send the response for us, okay? 133 00:06:08,210 --> 00:06:09,850 ‫So, let's copy this one 134 00:06:09,850 --> 00:06:12,410 ‫and put it in all the other handlers 135 00:06:12,410 --> 00:06:15,600 ‫that query documents based on the ID. 136 00:06:15,600 --> 00:06:20,470 ‫So, not create tour but update a tour, okay? 137 00:06:20,470 --> 00:06:21,380 ‫And so, here the same, 138 00:06:21,380 --> 00:06:23,120 ‫if we're trying to update the tour 139 00:06:23,120 --> 00:06:24,360 ‫that does not exist, 140 00:06:24,360 --> 00:06:26,773 ‫it will then give us the exact same error. 141 00:06:29,210 --> 00:06:32,470 ‫Finally of course the same with delete. 142 00:06:32,470 --> 00:06:35,870 ‫And now you see that ESLint gave me this error here 143 00:06:35,870 --> 00:06:38,710 ‫and so, that's because this tour is not defined 144 00:06:38,710 --> 00:06:41,730 ‫and in this case, ESLint really saved me here 145 00:06:41,730 --> 00:06:43,660 ‫from creating this bug. 146 00:06:43,660 --> 00:06:44,550 ‫Right? 147 00:06:44,550 --> 00:06:46,790 ‫So, again without ESLint, 148 00:06:46,790 --> 00:06:48,570 ‫I would have probably just pasted it here 149 00:06:48,570 --> 00:06:49,920 ‫and called it a day 150 00:06:49,920 --> 00:06:53,050 ‫without even noticing that tour is nowhere defined 151 00:06:53,050 --> 00:06:54,600 ‫inside of this function 152 00:06:54,600 --> 00:06:57,830 ‫but since we installed this really valuable tool, 153 00:06:57,830 --> 00:06:59,970 ‫I can now go ahead and fix it. 154 00:06:59,970 --> 00:07:01,820 ‫All right, so up until this point, 155 00:07:01,820 --> 00:07:06,490 ‫we simply awaited this delete instruction here 156 00:07:06,490 --> 00:07:08,460 ‫and didn't save the result of it 157 00:07:08,460 --> 00:07:10,710 ‫and that's simply because we didn't need it. 158 00:07:10,710 --> 00:07:13,200 ‫Okay, but right now we actually do need it 159 00:07:13,200 --> 00:07:15,140 ‫because we want this tour variable 160 00:07:15,140 --> 00:07:18,413 ‫in order to verify if there actually is a tour or not. 161 00:07:21,460 --> 00:07:23,760 ‫So, very easy, const tour 162 00:07:23,760 --> 00:07:25,350 ‫and then equal to that result, 163 00:07:25,350 --> 00:07:27,450 ‫give it a save and then the error is gone. 164 00:07:28,610 --> 00:07:29,820 ‫So, great. 165 00:07:29,820 --> 00:07:32,770 ‫ESLint at work, all right? 166 00:07:32,770 --> 00:07:37,770 ‫Now maybe you noticed that I did not add this 404 error here 167 00:07:37,950 --> 00:07:40,000 ‫in this getAllTour handler. 168 00:07:40,000 --> 00:07:41,910 ‫So, why did I did that? 169 00:07:41,910 --> 00:07:43,620 ‫And so let me explain you why. 170 00:07:43,620 --> 00:07:46,330 ‫So, when there is zero results found, 171 00:07:46,330 --> 00:07:50,530 ‫for example, there are no results matching for a filter, 172 00:07:50,530 --> 00:07:52,520 ‫or because the page was requested 173 00:07:52,520 --> 00:07:55,970 ‫that doesn't exist, then of course we could consider sending 174 00:07:55,970 --> 00:07:58,550 ‫a 404 error and saying that the data 175 00:07:58,550 --> 00:08:01,220 ‫was not found but in my opinion 176 00:08:01,220 --> 00:08:03,760 ‫and also the opinion of other developers, 177 00:08:03,760 --> 00:08:07,170 ‫that is not entirely correct in this request 178 00:08:07,170 --> 00:08:09,240 ‫because there was not really an error. 179 00:08:09,240 --> 00:08:11,950 ‫I mean, the request was correctly received. 180 00:08:11,950 --> 00:08:14,550 ‫The database correctly searched for the tours 181 00:08:14,550 --> 00:08:16,950 ‫and found exactly zero records 182 00:08:16,950 --> 00:08:19,150 ‫and so, these zero records are exactly 183 00:08:19,150 --> 00:08:23,250 ‫what we're gonna send back along with the 200 HTTP code. 184 00:08:23,250 --> 00:08:25,120 ‫All right, so again I consider 185 00:08:25,120 --> 00:08:27,300 ‫that there cannot really be an error 186 00:08:27,300 --> 00:08:29,610 ‫when a user requests all the tours 187 00:08:29,610 --> 00:08:32,680 ‫unless of course there is some failure in the database 188 00:08:32,680 --> 00:08:33,850 ‫or something like that. 189 00:08:33,850 --> 00:08:35,210 ‫But in that case, Mongoose 190 00:08:35,210 --> 00:08:37,600 ‫will then automatically throw an error. 191 00:08:37,600 --> 00:08:40,950 ‫Right, which then in turn is gonna get catched 192 00:08:40,950 --> 00:08:42,920 ‫by our or catchAsync function 193 00:08:42,920 --> 00:08:44,330 ‫and as you already know, 194 00:08:44,330 --> 00:08:47,510 ‫handled in our global error handler 195 00:08:47,510 --> 00:08:48,800 ‫and as you already know, 196 00:08:48,800 --> 00:08:52,000 ‫handled in our global error handling middleware. 197 00:08:52,000 --> 00:08:55,640 ‫All right, so I've said these words so many times by now. 198 00:08:55,640 --> 00:08:57,717 ‫Anyway, I hope that made sense 199 00:08:57,717 --> 00:09:01,113 ‫and so, yeah, let's now move on.