1 00:00:01,210 --> 00:00:02,660 ‫So far in this section, 2 00:00:02,660 --> 00:00:04,860 ‫we have talked about Mongoose models, 3 00:00:04,860 --> 00:00:06,940 ‫CRUD operations with Mongoose, 4 00:00:06,940 --> 00:00:09,660 ‫we did a lot of querying, and we learned about 5 00:00:09,660 --> 00:00:12,820 ‫the aggregation pipeline, but now for the next 6 00:00:12,820 --> 00:00:15,110 ‫couple of videos, let's actually return 7 00:00:15,110 --> 00:00:18,860 ‫to our data model and learn some super useful features 8 00:00:18,860 --> 00:00:22,170 ‫that Mongoose offers us in order to model our data. 9 00:00:22,170 --> 00:00:24,090 ‫And the first one we're gonna talk about 10 00:00:24,090 --> 00:00:25,773 ‫are virtual properties. 11 00:00:27,410 --> 00:00:29,973 ‫And so let's open our tour model here. 12 00:00:31,050 --> 00:00:35,080 ‫All right, now virtual properties are basically fields 13 00:00:35,080 --> 00:00:37,030 ‫that we can define on our schema 14 00:00:37,030 --> 00:00:39,150 ‫but that will not be persisted. 15 00:00:39,150 --> 00:00:42,100 ‫So they will not be saved into the database 16 00:00:42,100 --> 00:00:44,720 ‫in order to save us some space there. 17 00:00:44,720 --> 00:00:46,140 ‫And most of the time, of course, 18 00:00:46,140 --> 00:00:49,260 ‫we want to really save our data to the database, 19 00:00:49,260 --> 00:00:51,700 ‫but virtual properties make a lot of sense 20 00:00:51,700 --> 00:00:55,090 ‫for fields that can be derived from one another. 21 00:00:55,090 --> 00:00:58,410 ‫For example a conversion from miles to kilometers, 22 00:00:58,410 --> 00:01:00,720 ‫it doesn't make sense to store these two fields 23 00:01:00,720 --> 00:01:03,260 ‫in a database if we can easily convert 24 00:01:03,260 --> 00:01:05,750 ‫one to the other, right? 25 00:01:05,750 --> 00:01:09,140 ‫Okay, so let's now define a virtual property 26 00:01:09,140 --> 00:01:11,680 ‫that contains the tour duration in weeks. 27 00:01:11,680 --> 00:01:13,800 ‫And so that's a field basically 28 00:01:13,800 --> 00:01:16,460 ‫that we can very easily convert from the duration 29 00:01:16,460 --> 00:01:18,970 ‫that we already have in days, right? 30 00:01:18,970 --> 00:01:20,523 ‫And so here is how it works. 31 00:01:22,160 --> 00:01:25,640 ‫We define that virtual properties on the tour schema, 32 00:01:25,640 --> 00:01:30,640 ‫and so we say, tourSchema.virtual and then the name 33 00:01:33,430 --> 00:01:34,763 ‫of the virtual property. 34 00:01:36,530 --> 00:01:39,300 ‫So let's call it duration weeks, 35 00:01:39,300 --> 00:01:42,950 ‫and then on there we need to define the get method. 36 00:01:42,950 --> 00:01:45,600 ‫And that's just because this virtual property here 37 00:01:45,600 --> 00:01:47,580 ‫will basically be created each time 38 00:01:47,580 --> 00:01:50,560 ‫that we get some data out of the database. 39 00:01:50,560 --> 00:01:54,273 ‫And so this get function here is called a getter. 40 00:01:54,273 --> 00:01:57,090 ‫Now in here we pass a function, 41 00:01:57,090 --> 00:01:58,400 ‫and actually this call back function 42 00:01:58,400 --> 00:02:02,460 ‫is gonna be a real function, so not an arrow function, 43 00:02:02,460 --> 00:02:05,672 ‫and I'm gonna explain to you why in a second. 44 00:02:05,672 --> 00:02:08,500 ‫Now how do we then basically define 45 00:02:08,500 --> 00:02:10,810 ‫the virtual property? 46 00:02:10,810 --> 00:02:13,420 ‫Well it's very simple, all we have to say 47 00:02:13,420 --> 00:02:18,280 ‫is that we want to return this, .duration in this case, 48 00:02:18,280 --> 00:02:19,833 ‫divided by seven. 49 00:02:21,020 --> 00:02:24,350 ‫So this is how we calculate the duration in weeks, 50 00:02:24,350 --> 00:02:26,730 ‫so the duration in days divided by seven 51 00:02:26,730 --> 00:02:29,110 ‫because there are seven days in the week, 52 00:02:29,110 --> 00:02:31,030 ‫and so that's then the duration in weeks. 53 00:02:31,030 --> 00:02:33,510 ‫For example, if a tour has seven days, 54 00:02:33,510 --> 00:02:35,730 ‫then it's of course gonna be one week. 55 00:02:35,730 --> 00:02:38,360 ‫Now I used this regular function here 56 00:02:38,360 --> 00:02:41,250 ‫because remember, an arrow function does not get 57 00:02:41,250 --> 00:02:43,060 ‫its own disk keyword. 58 00:02:43,060 --> 00:02:45,800 ‫In here we actually need the disk keyword 59 00:02:45,800 --> 00:02:48,470 ‫because the disk keyword in this case 60 00:02:48,470 --> 00:02:51,588 ‫is going to be pointing to the current document. 61 00:02:51,588 --> 00:02:54,640 ‫And so usually when we want to use this, 62 00:02:54,640 --> 00:02:58,714 ‫then we should always use a regular function. 63 00:02:58,714 --> 00:03:01,140 ‫So really everywhere in Mongoose, 64 00:03:01,140 --> 00:03:04,340 ‫I'm gonna always be using these regular functions 65 00:03:04,340 --> 00:03:06,061 ‫that we're used to. 66 00:03:06,061 --> 00:03:11,061 ‫So give it a save here, and that's actually it. 67 00:03:11,070 --> 00:03:13,180 ‫That's how we define duration weeks, 68 00:03:13,180 --> 00:03:15,660 ‫which is not going to be persisted in the database, 69 00:03:15,660 --> 00:03:19,150 ‫but it's only gonna be there as soon as we get the data. 70 00:03:19,150 --> 00:03:21,820 ‫Now right now it's actually not gonna be there yet, 71 00:03:21,820 --> 00:03:24,610 ‫because there's one piece missing here, 72 00:03:24,610 --> 00:03:27,243 ‫so let me start by showing you that. 73 00:03:28,760 --> 00:03:31,240 ‫So if we try to get all tours, 74 00:03:31,240 --> 00:03:34,050 ‫you will see that duration weeks is nowhere 75 00:03:34,050 --> 00:03:35,768 ‫to be found here. 76 00:03:35,768 --> 00:03:38,660 ‫And that's because we need to explicitly define 77 00:03:38,660 --> 00:03:41,740 ‫in our schema that we want the virtual properties 78 00:03:41,740 --> 00:03:42,683 ‫in our output. 79 00:03:43,758 --> 00:03:48,758 ‫And so remember how I said that into this Mongoose.schema, 80 00:03:49,320 --> 00:03:51,650 ‫we can pass in not only the object 81 00:03:51,650 --> 00:03:54,050 ‫with the schema definition itself, 82 00:03:54,050 --> 00:03:56,943 ‫but also an object for the schema options. 83 00:03:58,070 --> 00:04:00,579 ‫And so let's add that here at the end, 84 00:04:00,579 --> 00:04:04,810 ‫so this first object here is the schema definition, 85 00:04:04,810 --> 00:04:07,630 ‫and now second an object for the options. 86 00:04:07,630 --> 00:04:11,260 ‫And what we need to specify here is the two JSON 87 00:04:12,390 --> 00:04:15,410 ‫property here, and what we say is then 88 00:04:15,410 --> 00:04:19,453 ‫that each time that the data is actually outputted as JSON, 89 00:04:20,480 --> 00:04:22,710 ‫we want virtuals to be true. 90 00:04:23,681 --> 00:04:26,657 ‫So basically the virtuals to be part of the output. 91 00:04:27,800 --> 00:04:30,000 ‫And now I'm duplicating this because we also 92 00:04:30,000 --> 00:04:31,923 ‫want to say to object. 93 00:04:33,370 --> 00:04:36,037 ‫So basically when the data gets outputted 94 00:04:36,037 --> 00:04:37,320 ‫as an object. 95 00:04:37,320 --> 00:04:40,010 ‫And so if we now go back here, we should then 96 00:04:40,010 --> 00:04:41,993 ‫be able to see duration weeks. 97 00:04:43,120 --> 00:04:46,550 ‫Let's wait for it, and indeed, here it is. 98 00:04:46,550 --> 00:04:51,053 ‫So it's five days, and so that is 0.71 weeks. 99 00:04:52,250 --> 00:04:55,800 ‫Here we have seven days, and so that's one week. 100 00:04:55,800 --> 00:04:59,810 ‫Okay, so that actually works, great. 101 00:04:59,810 --> 00:05:01,680 ‫Now one thing that we need to keep in mind 102 00:05:01,680 --> 00:05:04,840 ‫is that we cannot use this virtual property here 103 00:05:04,840 --> 00:05:07,840 ‫in a query, because they're technically 104 00:05:07,840 --> 00:05:09,980 ‫not part of the database. 105 00:05:09,980 --> 00:05:11,370 ‫So we can not say, for example, 106 00:05:11,370 --> 00:05:16,370 ‫tour.find where duration weeks is equal to one. 107 00:05:16,618 --> 00:05:19,660 ‫That's not gonna work, again because this property 108 00:05:19,660 --> 00:05:22,520 ‫is not actually part of the database. 109 00:05:22,520 --> 00:05:25,330 ‫Now of course we could also have done this conversion 110 00:05:25,330 --> 00:05:28,450 ‫each time after we query the data, for example, 111 00:05:28,450 --> 00:05:30,890 ‫like in a controller, but that would not 112 00:05:30,890 --> 00:05:34,240 ‫be the best practice simply because we want to try 113 00:05:34,240 --> 00:05:36,960 ‫to keep business logic and application logic 114 00:05:36,960 --> 00:05:39,830 ‫as much separated as possible, remember? 115 00:05:39,830 --> 00:05:42,980 ‫So that was that whole talk about fat models 116 00:05:42,980 --> 00:05:46,950 ‫and thin controllers that we talked about before 117 00:05:46,950 --> 00:05:48,850 ‫which says that we should have models 118 00:05:48,850 --> 00:05:52,390 ‫with as much business logic as we can offload to them 119 00:05:52,390 --> 00:05:54,460 ‫and thin controllers with as little 120 00:05:54,460 --> 00:05:56,598 ‫business logic as possible. 121 00:05:56,598 --> 00:05:59,840 ‫And so virtual properties like this are actually 122 00:05:59,840 --> 00:06:01,970 ‫a good example of how we can achieve 123 00:06:01,970 --> 00:06:03,483 ‫that kind of architecture. 124 00:06:04,410 --> 00:06:06,460 ‫So knowing the duration in weeks 125 00:06:06,460 --> 00:06:09,070 ‫is a business logic because it has to do 126 00:06:09,070 --> 00:06:11,900 ‫with the business itself, not with stuff like requests 127 00:06:11,900 --> 00:06:14,550 ‫or responses, and so we do the calculation 128 00:06:14,550 --> 00:06:16,460 ‫right in the model where it belongs 129 00:06:16,460 --> 00:06:17,863 ‫and not in the controller.