1
00:00:01,300 --> 00:00:03,180
‫Remember how we have a field

2
00:00:03,180 --> 00:00:06,500
‫for the average rating on each tour document?

3
00:00:06,500 --> 00:00:09,860
‫Well up until this point that field doesn't really hold

4
00:00:09,860 --> 00:00:12,110
‫any meaningful data, does it?

5
00:00:12,110 --> 00:00:14,290
‫But so let's now actually change that

6
00:00:14,290 --> 00:00:17,233
‫and calculate average ratings in this lecture.

7
00:00:18,920 --> 00:00:22,410
‫So storing a summary of a related data set

8
00:00:22,410 --> 00:00:26,270
‫on the main data set is actually a very popular technique

9
00:00:26,270 --> 00:00:29,900
‫in data modeling that I hadn't actually mentioned yet.

10
00:00:29,900 --> 00:00:32,720
‫And this technique can actually be really helpful

11
00:00:32,720 --> 00:00:34,750
‫in order to prevent constant queries

12
00:00:34,750 --> 00:00:36,890
‫of the related data set.

13
00:00:36,890 --> 00:00:40,110
‫So in our application a great example of this technique

14
00:00:40,110 --> 00:00:43,320
‫is to store the average rating and the number of ratings

15
00:00:43,320 --> 00:00:46,870
‫on each tour, so that we don't have to query the reviews

16
00:00:46,870 --> 00:00:49,860
‫and calculate that average each time that we query

17
00:00:49,860 --> 00:00:52,150
‫for all the tours, okay.

18
00:00:52,150 --> 00:00:54,380
‫For example, that could become very useful

19
00:00:54,380 --> 00:00:57,280
‫for a tour overview page in our front-end

20
00:00:57,280 --> 00:01:00,320
‫where we really do not want to display all the reviews,

21
00:01:00,320 --> 00:01:03,350
‫but still want to show a summary of these reviews,

22
00:01:03,350 --> 00:01:06,730
‫like for example, the number of ratings and the average.

23
00:01:06,730 --> 00:01:09,130
‫And actually we already have the fields for that

24
00:01:09,130 --> 00:01:10,433
‫in our tour schema.

25
00:01:11,450 --> 00:01:15,870
‫So right here at the beginning, I think.

26
00:01:15,870 --> 00:01:17,660
‫Yeah, so we have the ratings average

27
00:01:17,660 --> 00:01:19,760
‫and ratings quantity right here,

28
00:01:19,760 --> 00:01:22,380
‫but right now they're only just some numbers

29
00:01:22,380 --> 00:01:25,307
‫and of course, they are not the actual average

30
00:01:25,307 --> 00:01:27,560
‫and the number of ratings, because we never

31
00:01:27,560 --> 00:01:30,840
‫really calculated that at any point in our application,

32
00:01:30,840 --> 00:01:34,290
‫but that's exactly what we're gonna change in this video.

33
00:01:34,290 --> 00:01:37,370
‫So right now we're gonna calculate the average rating

34
00:01:37,370 --> 00:01:39,750
‫and also the number of ratings of a tour

35
00:01:39,750 --> 00:01:43,330
‫each time that a new review is added to that tour

36
00:01:43,330 --> 00:01:47,000
‫or also when a review is updated or deleted,

37
00:01:47,000 --> 00:01:49,230
‫because that's exactly the situations

38
00:01:49,230 --> 00:01:52,830
‫when the number or the average might change, right.

39
00:01:52,830 --> 00:01:55,920
‫So how are we actually going to implement this?

40
00:01:55,920 --> 00:01:58,800
‫Well back here in the review model

41
00:01:58,800 --> 00:02:00,620
‫we're gonna create a new function

42
00:02:00,620 --> 00:02:02,690
‫which will take in a tour ID

43
00:02:02,690 --> 00:02:05,690
‫and calculate the average rating and the number of ratings

44
00:02:05,690 --> 00:02:09,410
‫that exist in our collection for that exact tour.

45
00:02:09,410 --> 00:02:11,880
‫Then in the end the function will even update

46
00:02:11,880 --> 00:02:14,020
‫the corresponding tour document.

47
00:02:14,020 --> 00:02:16,360
‫Then in order to use that function

48
00:02:16,360 --> 00:02:19,510
‫we will use middleware to basically call this function

49
00:02:19,510 --> 00:02:22,650
‫each time that there is a new review or one is updated

50
00:02:22,650 --> 00:02:24,980
‫or deleted, okay.

51
00:02:24,980 --> 00:02:28,030
‫So let's now start by writing that function

52
00:02:28,030 --> 00:02:31,370
‫and for that we're actually gonna write a static method

53
00:02:31,370 --> 00:02:34,510
‫on our schema, and that's a feature of Mongoose

54
00:02:34,510 --> 00:02:36,580
‫that we hadn't used yet.

55
00:02:36,580 --> 00:02:38,630
‫So we only used instance method,

56
00:02:38,630 --> 00:02:40,500
‫which we can call on documents

57
00:02:40,500 --> 00:02:42,050
‫and they are also very useful,

58
00:02:42,050 --> 00:02:46,090
‫but this time we're really going to use static methods.

59
00:02:46,090 --> 00:02:46,923
‫Okay.

60
00:02:47,850 --> 00:02:51,330
‫So again, these can be called on the model

61
00:02:51,330 --> 00:02:55,157
‫directly, for example, like this review.calcStats,

62
00:02:58,010 --> 00:02:59,520
‫okay.

63
00:02:59,520 --> 00:03:04,350
‫And the way this works is of course reviewSchema

64
00:03:04,350 --> 00:03:09,323
‫and then .statics and then the name of the function.

65
00:03:10,490 --> 00:03:11,540
‫So calcAverageRatings

66
00:03:18,360 --> 00:03:22,143
‫is equal to a function, which remember takes in a tour ID,

67
00:03:24,800 --> 00:03:27,180
‫and that ID is of course for the tour

68
00:03:27,180 --> 00:03:29,670
‫to which the current review belongs to.

69
00:03:29,670 --> 00:03:32,790
‫And I know that at this point it's probably all sounds

70
00:03:32,790 --> 00:03:35,000
‫kind of confusing, but don't worry

71
00:03:35,000 --> 00:03:36,720
‫once we have all of this implemented

72
00:03:36,720 --> 00:03:38,380
‫and also when we're testing it

73
00:03:38,380 --> 00:03:42,080
‫it will then make a lot of sense in practice, okay?

74
00:03:42,080 --> 00:03:45,120
‫Anyway in order to now actually do the calculation

75
00:03:45,120 --> 00:03:48,470
‫we will again use the aggregation pipeline, right.

76
00:03:48,470 --> 00:03:53,470
‫So let's remember that in our tool controller,

77
00:03:53,970 --> 00:03:56,990
‫so right here we use the aggregation pipeline

78
00:03:56,990 --> 00:04:00,730
‫to also create some statistics like this, okay.

79
00:04:00,730 --> 00:04:04,560
‫So we used the aggregate method, which we called directly

80
00:04:04,560 --> 00:04:06,670
‫on the model, okay.

81
00:04:06,670 --> 00:04:09,080
‫So now in our instance method we can actually do

82
00:04:09,080 --> 00:04:10,393
‫the exact same thing.

83
00:04:12,140 --> 00:04:15,690
‫So in a static method like this these keywords

84
00:04:15,690 --> 00:04:18,130
‫actually points to the current model.

85
00:04:18,130 --> 00:04:20,623
‫So that's why we can use this.aggregate,

86
00:04:22,160 --> 00:04:25,100
‫because remember we need to call this.aggregate

87
00:04:25,100 --> 00:04:27,470
‫on the model directly, and that's exactly

88
00:04:27,470 --> 00:04:30,970
‫why we're using a static method here in the first place.

89
00:04:30,970 --> 00:04:33,690
‫Because again this now points to the model

90
00:04:33,690 --> 00:04:38,200
‫and we need to call aggregate always on the model, okay.

91
00:04:38,200 --> 00:04:41,610
‫So into aggregate we need to pass in an array

92
00:04:41,610 --> 00:04:45,850
‫of all the stages that we want in aggregate, okay.

93
00:04:45,850 --> 00:04:47,930
‫So what do we want to do first?

94
00:04:47,930 --> 00:04:51,930
‫Well the first step should be to select all the reviews

95
00:04:51,930 --> 00:04:54,280
‫that actually belong to the current tour

96
00:04:54,280 --> 00:04:57,470
‫that was passed in as the argument.

97
00:04:57,470 --> 00:04:58,790
‫Okay.

98
00:04:58,790 --> 00:05:02,093
‫So our first stage is a match stage,

99
00:05:03,090 --> 00:05:03,933
‫remember that,

100
00:05:05,360 --> 00:05:07,580
‫and so in here we passed our filter object

101
00:05:08,620 --> 00:05:11,420
‫and we can say tour equal to tour,

102
00:05:11,420 --> 00:05:13,740
‫but we don't really need that, as you already know,

103
00:05:13,740 --> 00:05:17,950
‫and so let's just remove this part, or actually

104
00:05:17,950 --> 00:05:20,670
‫just to make it a bit less confusing here with the names

105
00:05:20,670 --> 00:05:24,290
‫let's call this one here tour ID, okay.

106
00:05:24,290 --> 00:05:26,620
‫So tourId in here,

107
00:05:26,620 --> 00:05:27,480
‫okay.

108
00:05:27,480 --> 00:05:29,510
‫So like this we only select a tour

109
00:05:29,510 --> 00:05:33,330
‫that we actually want to update, okay.

110
00:05:33,330 --> 00:05:35,740
‫Now in the next stage let's actually calculate

111
00:05:35,740 --> 00:05:37,930
‫the statistics themselves,

112
00:05:37,930 --> 00:05:41,033
‫and for that we use a group stage.

113
00:05:42,920 --> 00:05:44,900
‫And in the group phase remember

114
00:05:44,900 --> 00:05:49,900
‫the first field that we need to specify is the ID, so _id

115
00:05:50,240 --> 00:05:51,740
‫and then the common field

116
00:05:51,740 --> 00:05:53,570
‫that all of the documents have in common

117
00:05:53,570 --> 00:05:56,200
‫that we want to group by and so that's again

118
00:05:56,200 --> 00:05:57,543
‫going to be the tour.

119
00:06:00,230 --> 00:06:04,460
‫So just like in our previous statistic calculation example

120
00:06:04,460 --> 00:06:07,310
‫here we grouped by the difficulty.

121
00:06:07,310 --> 00:06:10,250
‫So like this we calculate the statistics for easy

122
00:06:10,250 --> 00:06:11,840
‫and statistics for medium

123
00:06:11,840 --> 00:06:14,560
‫and then statistics for difficult tours.

124
00:06:14,560 --> 00:06:17,140
‫So in this example, we grouped all the tours together

125
00:06:17,140 --> 00:06:18,453
‫by their difficulty,

126
00:06:19,450 --> 00:06:20,283
‫okay.

127
00:06:20,283 --> 00:06:22,810
‫But here, of course we're grouping all the tours together

128
00:06:22,810 --> 00:06:23,663
‫by tour.

129
00:06:25,440 --> 00:06:26,273
‫Great.

130
00:06:26,273 --> 00:06:28,023
‫Now the number of ratings,

131
00:06:31,290 --> 00:06:32,653
‫remember how we do that,

132
00:06:33,690 --> 00:06:35,970
‫so all we do is to basically add one

133
00:06:35,970 --> 00:06:37,970
‫for each tour that we have,

134
00:06:37,970 --> 00:06:41,570
‫so each tour that was matched in the previous step, okay.

135
00:06:41,570 --> 00:06:44,810
‫So if there are five review documents for the current tour

136
00:06:44,810 --> 00:06:48,310
‫then for each of these documents one will get added.

137
00:06:48,310 --> 00:06:51,310
‫So then in the end the number of ratings will be five,

138
00:06:51,310 --> 00:06:55,130
‫and again, because of course we have five review documents.

139
00:06:55,130 --> 00:06:57,083
‫So that makes sense, right?

140
00:06:58,532 --> 00:07:03,532
‫Then also the average rating, which just like before

141
00:07:03,970 --> 00:07:08,970
‫we use the average operator and this needs to be inside

142
00:07:09,180 --> 00:07:10,013
‫an object

143
00:07:12,490 --> 00:07:14,440
‫and in here the name of the field

144
00:07:15,470 --> 00:07:18,330
‫which is the rating, right.

145
00:07:18,330 --> 00:07:22,180
‫So remember how each review has a rating field.

146
00:07:22,180 --> 00:07:24,993
‫So that's where we want to calculate the average from.

147
00:07:27,720 --> 00:07:30,350
‫Okay, and that's actually it.

148
00:07:30,350 --> 00:07:32,950
‫So number and average of ratings

149
00:07:32,950 --> 00:07:36,790
‫is exactly what we wanted to calculate in this aggregation.

150
00:07:36,790 --> 00:07:39,740
‫Now keep in mind that this actually returns a promise

151
00:07:39,740 --> 00:07:43,290
‫and so we need to await that and then store it

152
00:07:43,290 --> 00:07:46,193
‫into a variable called stats.

153
00:07:49,070 --> 00:07:49,980
‫Okay.

154
00:07:49,980 --> 00:07:53,023
‫Then mark this one here as async as well,

155
00:07:54,600 --> 00:07:55,620
‫give it a save

156
00:07:55,620 --> 00:07:59,790
‫and so now we actually need to use that stats variable.

157
00:07:59,790 --> 00:08:02,930
‫For now all I really want to do just to test this

158
00:08:02,930 --> 00:08:06,073
‫is to actually log the statistics to the console.

159
00:08:08,120 --> 00:08:09,090
‫Console.log

160
00:08:10,600 --> 00:08:11,433
‫stats.

161
00:08:13,640 --> 00:08:16,880
‫Okay, then in the later step we will actually want to,

162
00:08:16,880 --> 00:08:19,950
‫as I mentioned before then update the tour document

163
00:08:19,950 --> 00:08:21,770
‫with these statistics,

164
00:08:21,770 --> 00:08:23,930
‫but I'm gonna leave that for a bit later,

165
00:08:23,930 --> 00:08:26,070
‫because for now we actually need to call

166
00:08:26,070 --> 00:08:28,390
‫this method here somewhere, because otherwise

167
00:08:28,390 --> 00:08:31,133
‫the statistics here will never get called.

168
00:08:32,100 --> 00:08:33,863
‫And remember how we said at the beginning

169
00:08:33,863 --> 00:08:36,160
‫that we will do this using middleware

170
00:08:36,160 --> 00:08:38,523
‫each time that a new review is created.

171
00:08:40,050 --> 00:08:44,250
‫So let's implement that using reviewSchema pre

172
00:08:45,330 --> 00:08:46,163
‫save

173
00:08:50,680 --> 00:08:54,563
‫and then just our normal regular middleware function here.

174
00:08:55,860 --> 00:08:57,873
‫And remember that in this kind of middleware

175
00:08:57,873 --> 00:09:00,093
‫that this keyword points to the document

176
00:09:00,093 --> 00:09:02,210
‫that is currently being saved.

177
00:09:02,210 --> 00:09:04,760
‫So this points to

178
00:09:06,540 --> 00:09:08,850
‫current review, okay.

179
00:09:08,850 --> 00:09:11,880
‫So we will want to call the calcAverageRating function

180
00:09:11,880 --> 00:09:15,020
‫using this.tour, right.

181
00:09:15,020 --> 00:09:18,770
‫Now how are we actually going to call this function?

182
00:09:18,770 --> 00:09:19,940
‫Remember how I said that

183
00:09:19,940 --> 00:09:22,470
‫this function is available on the model.

184
00:09:22,470 --> 00:09:25,050
‫So basically like this put

185
00:09:25,050 --> 00:09:27,390
‫review.calcAverageRatings

186
00:09:29,557 --> 00:09:32,550
‫and then as I said we want to use this.tour,

187
00:09:34,340 --> 00:09:35,173
‫okay.

188
00:09:35,173 --> 00:09:37,240
‫And again, because this is the current review

189
00:09:37,240 --> 00:09:40,340
‫and this is then the tour ID that we're gonna pass

190
00:09:40,340 --> 00:09:42,143
‫inside of the calcAverageRatings.

191
00:09:43,640 --> 00:09:46,950
‫Now the problem is that at this point here in the code

192
00:09:46,950 --> 00:09:50,200
‫the review variable is not yet defined.

193
00:09:50,200 --> 00:09:53,340
‫Now you might think that the simple solution would be to

194
00:09:53,340 --> 00:09:57,780
‫simply move this code in here after this review declaration,

195
00:09:57,780 --> 00:10:00,480
‫but unfortunately that's not going to work,

196
00:10:00,480 --> 00:10:03,630
‫because just like in Express this code here basically runs

197
00:10:03,630 --> 00:10:05,730
‫in the sequence it is declared.

198
00:10:05,730 --> 00:10:08,100
‫So if we were to put this code here

199
00:10:08,100 --> 00:10:11,550
‫after the review declaration then this reviewSchema here

200
00:10:11,550 --> 00:10:13,810
‫would not contain this middleware,

201
00:10:13,810 --> 00:10:16,050
‫because we would then only be declaring it

202
00:10:16,050 --> 00:10:19,750
‫after the review model was already created, okay,

203
00:10:19,750 --> 00:10:23,160
‫but there is fortunately still a way around this

204
00:10:23,160 --> 00:10:26,273
‫and that is to use this.constructor.

205
00:10:28,970 --> 00:10:31,640
‫So this here still points to the model.

206
00:10:31,640 --> 00:10:35,267
‫You know, basically again this is the current document

207
00:10:35,267 --> 00:10:38,030
‫and the constructor is basically the model

208
00:10:38,030 --> 00:10:40,470
‫who created that document.

209
00:10:40,470 --> 00:10:42,410
‫So this here stands for the tour

210
00:10:42,410 --> 00:10:45,823
‫and so we can then simply do it like this.

211
00:10:47,420 --> 00:10:52,043
‫Then call next as always and that's actually it.

212
00:10:54,130 --> 00:10:57,320
‫So let's now go ahead and test this.

213
00:10:57,320 --> 00:11:00,500
‫And for doing that I will create a new tour first,

214
00:11:00,500 --> 00:11:02,670
‫because the other ones that we already have

215
00:11:02,670 --> 00:11:04,620
‫they have the average and number of ratings

216
00:11:04,620 --> 00:11:06,730
‫already calculated and so we really

217
00:11:06,730 --> 00:11:10,240
‫want to start from scratch here when testing this out.

218
00:11:10,240 --> 00:11:13,270
‫So to create a new tour we need to be logged in

219
00:11:13,270 --> 00:11:16,840
‫as administrators, and I think we currently are,

220
00:11:16,840 --> 00:11:18,940
‫but just to make sure let's do that again.

221
00:11:20,400 --> 00:11:21,233
‫Okay.

222
00:11:22,660 --> 00:11:24,981
‫So this is the new test tour.

223
00:11:24,981 --> 00:11:28,313
‫All right let's remove these here, they are not mandatory,

224
00:11:30,120 --> 00:11:32,663
‫and I think with this we're good to go.

225
00:11:36,950 --> 00:11:40,580
‫All right, and here you see the defaults that we set before

226
00:11:40,580 --> 00:11:43,130
‫so the ratings average for five

227
00:11:43,130 --> 00:11:46,430
‫and the quantity set to zero, okay.

228
00:11:46,430 --> 00:11:49,630
‫Now in order to create a new review

229
00:11:49,630 --> 00:11:52,560
‫we actually need to be logged in as a regular user,

230
00:11:52,560 --> 00:11:54,033
‫so not an administrator.

231
00:11:54,900 --> 00:11:58,900
‫So let's get a normal user, let's say.

232
00:11:58,900 --> 00:12:02,120
‫So let's just use this Laura here.

233
00:12:02,120 --> 00:12:03,470
‫So Laura@example.com

234
00:12:04,804 --> 00:12:08,063
‫and as I mentioned earlier the password is always the same.

235
00:12:12,000 --> 00:12:16,773
‫So let's do that and now we will create new review on tour.

236
00:12:17,920 --> 00:12:21,103
‫So now let's get the tour that we created earlier,

237
00:12:22,890 --> 00:12:26,653
‫so this ID and put it here in the URL.

238
00:12:27,880 --> 00:12:30,490
‫Okay, and so remember that this route

239
00:12:30,490 --> 00:12:33,877
‫now automatically gets a tour ID from the URL

240
00:12:33,877 --> 00:12:37,413
‫and a user ID from the currently logged in user,

241
00:12:38,730 --> 00:12:39,563
‫okay.

242
00:12:39,563 --> 00:12:42,063
‫So let's use this one as the first rating,

243
00:12:44,490 --> 00:12:48,643
‫let's send it, and now I want to take a look at our console.

244
00:12:50,060 --> 00:12:53,230
‫We have an output here, but for some reason it's only

245
00:12:53,230 --> 00:12:55,260
‫like this empty array.

246
00:12:55,260 --> 00:12:58,010
‫So something must not be working here.

247
00:12:58,010 --> 00:13:02,400
‫So let's take a look at the tour ID here just to make sure

248
00:13:02,400 --> 00:13:07,200
‫that we're getting the right value here, ID

249
00:13:07,200 --> 00:13:09,340
‫and let's also comment out this part here

250
00:13:10,210 --> 00:13:14,220
‫just to see if maybe there's some error in this part,

251
00:13:14,220 --> 00:13:17,360
‫and so let's now try it again.

252
00:13:17,360 --> 00:13:20,113
‫I'll simply add the same one here again, okay.

253
00:13:23,680 --> 00:13:26,453
‫Okay, so now we actually get something.

254
00:13:27,310 --> 00:13:29,790
‫So we have this one review which is

255
00:13:29,790 --> 00:13:32,210
‫the one that we created initially.

256
00:13:32,210 --> 00:13:34,900
‫So it starts with this ac15,

257
00:13:34,900 --> 00:13:39,623
‫but the one that I just created is this 66d, okay.

258
00:13:39,623 --> 00:13:44,223
‫So let's take a look at that here in Compass.

259
00:13:45,490 --> 00:13:47,223
‫So we need to go to the last page.

260
00:13:49,380 --> 00:13:52,450
‫Okay, and so the one that shows up in our console

261
00:13:52,450 --> 00:13:55,270
‫is only this one here, but not the second one

262
00:13:55,270 --> 00:13:57,730
‫that we just created, okay.

263
00:13:57,730 --> 00:13:59,670
‫So if we now create a third one

264
00:13:59,670 --> 00:14:02,980
‫then we should probably see the first and the second one.

265
00:14:02,980 --> 00:14:03,880
‫So let's try that.

266
00:14:12,060 --> 00:14:13,160
‫Okay.

267
00:14:13,160 --> 00:14:16,290
‫Send this one and now here in our output

268
00:14:18,060 --> 00:14:20,830
‫I actually get all three of them.

269
00:14:20,830 --> 00:14:23,793
‫So that doesn't make much sense,

270
00:14:24,800 --> 00:14:27,443
‫but anyway the point that I wanted to make here

271
00:14:27,443 --> 00:14:29,700
‫is that we shouldn't use pre,

272
00:14:29,700 --> 00:14:33,560
‫but instead we should use the post save middleware, okay.

273
00:14:33,560 --> 00:14:35,520
‫And that's because at pre save

274
00:14:35,520 --> 00:14:37,350
‫the current review is not really

275
00:14:37,350 --> 00:14:39,270
‫in the collection just yet.

276
00:14:39,270 --> 00:14:42,420
‫So therefore, when we then do this match here

277
00:14:42,420 --> 00:14:45,170
‫it shouldn't be able to then appear in the output here,

278
00:14:45,170 --> 00:14:47,150
‫because again at this point in time

279
00:14:47,150 --> 00:14:51,000
‫it's not really saved into the collection just yet, okay.

280
00:14:51,000 --> 00:14:52,760
‫So it's best to use post here,

281
00:14:52,760 --> 00:14:54,770
‫because at that time, of course,

282
00:14:54,770 --> 00:14:57,820
‫all the documents are already saved in the database

283
00:14:57,820 --> 00:14:59,330
‫and so that's then a great time

284
00:14:59,330 --> 00:15:02,430
‫to actually do this calculation with all the reviews already

285
00:15:02,430 --> 00:15:04,723
‫and then store the result on the tour.

286
00:15:05,940 --> 00:15:07,750
‫Okay, so I'm not really sure

287
00:15:07,750 --> 00:15:10,403
‫why this one here actually showed up at this point,

288
00:15:11,670 --> 00:15:15,603
‫but anyway let's now try it with another one.

289
00:15:19,290 --> 00:15:21,280
‫So that's the fourth one,

290
00:15:21,280 --> 00:15:25,450
‫and now we get next is not a function and indeed

291
00:15:25,450 --> 00:15:27,930
‫as I mentioned earlier the post middleware

292
00:15:27,930 --> 00:15:30,250
‫does not get access to next

293
00:15:30,250 --> 00:15:33,940
‫and so therefore, we of course cannot call it,

294
00:15:33,940 --> 00:15:34,833
‫cannot use it.

295
00:15:37,070 --> 00:15:40,793
‫All right, and so here we have our next rating,

296
00:15:42,160 --> 00:15:42,993
‫okay.

297
00:15:42,993 --> 00:15:45,913
‫So it now shows up here as well.

298
00:15:48,090 --> 00:15:50,840
‫So we don't need that and now we can safely

299
00:15:50,840 --> 00:15:53,053
‫try to calculate our statistics here.

300
00:15:54,140 --> 00:15:56,600
‫Give it a save, and actually let's

301
00:15:56,600 --> 00:15:59,000
‫delete all of these reviews.

302
00:15:59,000 --> 00:16:03,623
‫So I basically want to start from scratch, okay.

303
00:16:04,880 --> 00:16:05,800
‫So

304
00:16:08,320 --> 00:16:11,190
‫all of these five reviews here should go

305
00:16:16,300 --> 00:16:18,450
‫and now we're ready to go.

306
00:16:18,450 --> 00:16:21,030
‫So let's actually create this one as the first one

307
00:16:22,860 --> 00:16:26,400
‫and now let's go ahead and take a look at our statistics

308
00:16:26,400 --> 00:16:27,600
‫and here we go.

309
00:16:27,600 --> 00:16:29,530
‫So this is the current tour ID

310
00:16:29,530 --> 00:16:31,670
‫then the number of ratings is one

311
00:16:31,670 --> 00:16:33,703
‫and the average is of course three.

312
00:16:35,510 --> 00:16:39,240
‫So if we add another one with the rating of five

313
00:16:40,920 --> 00:16:43,310
‫well then the average should be four

314
00:16:43,310 --> 00:16:46,010
‫and we should have the number of ratings equal to two.

315
00:16:47,840 --> 00:16:52,460
‫So let's try that and indeed just as I said

316
00:16:52,460 --> 00:16:55,480
‫two ratings, average of four.

317
00:16:55,480 --> 00:16:59,010
‫And just another one just to make really sure,

318
00:16:59,010 --> 00:17:00,610
‫let's add another one with five,

319
00:17:05,600 --> 00:17:07,240
‫and here we go.

320
00:17:07,240 --> 00:17:08,073
‫Great.

321
00:17:08,073 --> 00:17:10,990
‫So we're now correctly calculating the statistics,

322
00:17:10,990 --> 00:17:13,090
‫but of course they're not yet being persisted

323
00:17:13,090 --> 00:17:15,290
‫to the current tour document.

324
00:17:15,290 --> 00:17:18,630
‫So if we come here in Compass

325
00:17:18,630 --> 00:17:20,293
‫to the tour that we just created,

326
00:17:22,330 --> 00:17:24,340
‫probably it's the last one here.

327
00:17:24,340 --> 00:17:27,790
‫Yep, so our test tour, it still has these default values

328
00:17:27,790 --> 00:17:30,470
‫of 4.5 and zero,

329
00:17:30,470 --> 00:17:31,350
‫okay.

330
00:17:31,350 --> 00:17:33,260
‫So now it's time to actually persist

331
00:17:33,260 --> 00:17:36,573
‫the calculated statistics into this tour document,

332
00:17:38,250 --> 00:17:39,480
‫okay.

333
00:17:39,480 --> 00:17:41,670
‫And so let's do that.

334
00:17:41,670 --> 00:17:44,420
‫First of all, in order to be able to do that

335
00:17:44,420 --> 00:17:47,863
‫we need to require the tour model, right.

336
00:17:48,810 --> 00:17:49,643
‫So tour

337
00:17:51,620 --> 00:17:52,453
‫require

338
00:17:55,250 --> 00:17:56,483
‫and there we go.

339
00:18:03,860 --> 00:18:07,010
‫So what we need to do is to basically find

340
00:18:07,010 --> 00:18:10,160
‫the current tour and then update it.

341
00:18:10,160 --> 00:18:13,873
‫So we did that before many times, findById

342
00:18:14,830 --> 00:18:16,980
‫and update,

343
00:18:16,980 --> 00:18:17,813
‫okay.

344
00:18:17,813 --> 00:18:21,370
‫And the ID is of course the tour ID that was passed in

345
00:18:21,370 --> 00:18:23,670
‫into the function and then an object

346
00:18:23,670 --> 00:18:27,140
‫of the data that we actually want to update.

347
00:18:27,140 --> 00:18:30,470
‫So let's get these field names from here.

348
00:18:30,470 --> 00:18:32,500
‫So we have ratingsQuantity

349
00:18:34,970 --> 00:18:36,230
‫on one hand.

350
00:18:36,230 --> 00:18:39,260
‫Let's put it here to one for now

351
00:18:39,260 --> 00:18:41,240
‫just so we don't get an error

352
00:18:41,240 --> 00:18:42,893
‫and ratingsAverage.

353
00:18:46,910 --> 00:18:48,940
‫Again, to prevent any errors,

354
00:18:48,940 --> 00:18:50,650
‫because now I want to come here

355
00:18:50,650 --> 00:18:53,400
‫and take a look at these statistics.

356
00:18:53,400 --> 00:18:57,700
‫So you see they are stored in an array actually, okay.

357
00:18:57,700 --> 00:19:00,870
‫So we need to go to the first position of that array,

358
00:19:00,870 --> 00:19:02,433
‫which is where this object is.

359
00:19:04,520 --> 00:19:07,060
‫So stats at position zero

360
00:19:07,970 --> 00:19:12,820
‫and then from there we get the end rating property,

361
00:19:12,820 --> 00:19:13,653
‫okay.

362
00:19:13,653 --> 00:19:14,593
‫So this one here.

363
00:19:18,440 --> 00:19:21,283
‫And then of course the same for average rating.

364
00:19:23,870 --> 00:19:24,800
‫Okay.

365
00:19:24,800 --> 00:19:27,070
‫And now we also need to await it.

366
00:19:27,070 --> 00:19:31,640
‫So as always this returns a premise and so we can await it.

367
00:19:31,640 --> 00:19:34,750
‫Now we could also store the result of this to a variable,

368
00:19:34,750 --> 00:19:37,250
‫but we don't really need the tour at all.

369
00:19:37,250 --> 00:19:39,530
‫All we want to do is to really update it,

370
00:19:39,530 --> 00:19:40,880
‫and so we do not store

371
00:19:40,880 --> 00:19:43,700
‫the results value of the premise anywhere.

372
00:19:43,700 --> 00:19:44,960
‫Okay.

373
00:19:44,960 --> 00:19:49,960
‫So let's simply try to add another review here,

374
00:19:50,050 --> 00:19:53,373
‫this time with one terrible.

375
00:19:55,800 --> 00:19:56,810
‫Okay.

376
00:19:56,810 --> 00:20:00,650
‫And first of all, let's take a look at the statistics.

377
00:20:00,650 --> 00:20:03,300
‫So of course, we get the rating of four,

378
00:20:03,300 --> 00:20:06,203
‫so the number of ratings, and the average of 3.5.

379
00:20:07,270 --> 00:20:10,090
‫So now in order to really see if it worked

380
00:20:10,090 --> 00:20:13,290
‫let's check out Compass or we can also use

381
00:20:13,290 --> 00:20:15,223
‫or get tour end point,

382
00:20:16,270 --> 00:20:17,320
‫okay.

383
00:20:17,320 --> 00:20:20,593
‫So we need the tour ID, that we can copy from here,

384
00:20:23,550 --> 00:20:27,160
‫paste it here, and now comes the moment

385
00:20:27,160 --> 00:20:30,060
‫and indeed it worked,

386
00:20:30,060 --> 00:20:31,110
‫perfect.

387
00:20:31,110 --> 00:20:34,940
‫So that's awesome, absolutely fantastic.

388
00:20:34,940 --> 00:20:37,810
‫Just one more time for the fun of it

389
00:20:37,810 --> 00:20:39,893
‫let's add another review here.

390
00:20:44,330 --> 00:20:45,163
‫Okay.

391
00:20:45,163 --> 00:20:48,480
‫Update this one, and so now we get five

392
00:20:48,480 --> 00:20:51,760
‫and our average went up by a little bit.

393
00:20:51,760 --> 00:20:52,593
‫Great.

394
00:20:52,593 --> 00:20:56,570
‫So let's now just take a second and recap what we did here.

395
00:20:56,570 --> 00:20:59,690
‫So we started by creating a static method.

396
00:20:59,690 --> 00:21:01,770
‫So this entire function here

397
00:21:01,770 --> 00:21:04,870
‫to basically create the statistics of the average

398
00:21:04,870 --> 00:21:07,980
‫and number of ratings for the tour ID

399
00:21:07,980 --> 00:21:12,230
‫for which the current review was created, okay.

400
00:21:12,230 --> 00:21:14,870
‫And we created this function as a static method,

401
00:21:14,870 --> 00:21:18,030
‫because we needed to call the aggregate function

402
00:21:18,030 --> 00:21:19,310
‫on the model.

403
00:21:19,310 --> 00:21:22,080
‫So in a static method to this variable

404
00:21:22,080 --> 00:21:23,910
‫calls exactly to a method.

405
00:21:23,910 --> 00:21:26,670
‫So it's very handy in these cases.

406
00:21:26,670 --> 00:21:29,930
‫So we constructed our aggregation pipeline here

407
00:21:29,930 --> 00:21:32,590
‫where we selected all the reviews that matched

408
00:21:32,590 --> 00:21:35,880
‫the current tour ID, and then they're calculated,

409
00:21:35,880 --> 00:21:38,470
‫the statistics for all of these reviews.

410
00:21:38,470 --> 00:21:40,520
‫Then after that was done

411
00:21:40,520 --> 00:21:45,470
‫we saved the statistics to the current tour, okay.

412
00:21:45,470 --> 00:21:47,690
‫Then in order to actually use this function

413
00:21:47,690 --> 00:21:52,570
‫we call it after a new review has been created, okay.

414
00:21:52,570 --> 00:21:55,620
‫For that we need to use this.constructor

415
00:21:55,620 --> 00:21:58,930
‫because this is what points to the current model.

416
00:21:58,930 --> 00:22:02,037
‫Now keep in mind how we said that we also want to update

417
00:22:02,037 --> 00:22:06,350
‫the statistics whenever a review is edited or deleted,

418
00:22:06,350 --> 00:22:08,090
‫because these actions will, of course,

419
00:22:08,090 --> 00:22:11,210
‫also influence the number and the average.

420
00:22:11,210 --> 00:22:13,960
‫However, doing so is a bit more complex.

421
00:22:13,960 --> 00:22:18,140
‫So since this video is already running pretty long

422
00:22:18,140 --> 00:22:20,493
‫let's actually leave that to the next one.