1 00:00:01,090 --> 00:00:04,160 ‫Querying for data in a database is one 2 00:00:04,160 --> 00:00:08,320 ‫of the most important operations that we have in databases. 3 00:00:08,320 --> 00:00:11,820 ‫And so, let's now take a look at a couple of query operators 4 00:00:11,820 --> 00:00:14,770 ‫in MongoDB, starting with some simple ones 5 00:00:14,770 --> 00:00:17,993 ‫and then moving on to some really complex queries. 6 00:00:19,610 --> 00:00:23,010 ‫And, to start, let's give ourselves some space here. 7 00:00:23,010 --> 00:00:25,760 ‫And so, you already know, the easiest way 8 00:00:25,760 --> 00:00:28,480 ‫to basically query for all the documents 9 00:00:28,480 --> 00:00:31,470 ‫in a certain collection is to just use find 10 00:00:31,470 --> 00:00:33,560 ‫without passing anything in there. 11 00:00:33,560 --> 00:00:36,130 ‫So, that's what we've been doing until this point. 12 00:00:36,130 --> 00:00:38,570 ‫And so, it gives us simply this result 13 00:00:38,570 --> 00:00:40,040 ‫with all the documents 14 00:00:40,040 --> 00:00:42,110 ‫that are in a certain collection basically 15 00:00:42,110 --> 00:00:44,620 ‫without any searching criteria. 16 00:00:44,620 --> 00:00:47,910 ‫But, now, let's say that we actually only want one tour 17 00:00:47,910 --> 00:00:49,540 ‫and we already know its name. 18 00:00:49,540 --> 00:00:51,610 ‫And so, we can search for that tour 19 00:00:51,610 --> 00:00:54,120 ‫using the name that we know. 20 00:00:54,120 --> 00:00:57,910 ‫And so, we us db.tours 21 00:00:59,150 --> 00:01:00,400 ‫and, again, find. 22 00:01:00,400 --> 00:01:03,573 ‫But, this time, we're gonna pass in a filter object. 23 00:01:04,930 --> 00:01:06,710 ‫So, again, we need an object here. 24 00:01:06,710 --> 00:01:09,580 ‫And so, you start to see now that in MongoDB, 25 00:01:09,580 --> 00:01:12,560 ‫really everything works with objects. 26 00:01:12,560 --> 00:01:15,330 ‫And, this will be even more prominent a bit later 27 00:01:15,330 --> 00:01:16,163 ‫in this lecture. 28 00:01:17,265 --> 00:01:20,790 ‫So, inside this object, we pass in the filter. 29 00:01:20,790 --> 00:01:22,650 ‫So, basically the search criteria 30 00:01:22,650 --> 00:01:25,050 ‫that we want to search for. 31 00:01:25,050 --> 00:01:28,343 ‫So, we simply set the name to the tour name 32 00:01:28,343 --> 00:01:30,570 ‫that we want to search for. 33 00:01:30,570 --> 00:01:32,120 ‫So, let's say The Forest Hiker. 34 00:01:35,040 --> 00:01:36,330 ‫And, that's actually it. 35 00:01:36,330 --> 00:01:39,750 ‫So, that is our search criteria or the search filter. 36 00:01:39,750 --> 00:01:41,260 ‫And, if we had returned now, 37 00:01:41,260 --> 00:01:43,580 ‫then we only get this one tour 38 00:01:43,580 --> 00:01:47,553 ‫where the name matches exactly the one that we passed in. 39 00:01:48,970 --> 00:01:51,830 ‫And, we could do, of course, the same for anything else. 40 00:01:51,830 --> 00:01:53,760 ‫For example, for the difficulty, 41 00:01:53,760 --> 00:01:57,800 ‫we could search for tours 42 00:01:57,800 --> 00:01:59,593 ‫that have an easy in difficulty. 43 00:02:01,890 --> 00:02:06,343 ‫So, difficulty and easy. 44 00:02:07,640 --> 00:02:10,030 ‫Close the object, close the function. 45 00:02:10,030 --> 00:02:13,910 ‫And so, we get all the tours where the difficulty is easy. 46 00:02:13,910 --> 00:02:16,420 ‫Right now, there is only one tour, 47 00:02:16,420 --> 00:02:19,010 ‫but if we had multiple tours with difficulty set 48 00:02:19,010 --> 00:02:20,260 ‫to easy, then, of course, 49 00:02:20,260 --> 00:02:23,020 ‫it would return all of these documents. 50 00:02:23,020 --> 00:02:25,150 ‫So, that is the easiest way 51 00:02:25,150 --> 00:02:27,400 ‫that we can search for documents. 52 00:02:27,400 --> 00:02:29,610 ‫Now, let's take it to the next level 53 00:02:29,610 --> 00:02:32,063 ‫by using some special query operators. 54 00:02:33,100 --> 00:02:36,070 ‫And, what I want to do is to search for tours 55 00:02:36,070 --> 00:02:38,673 ‫which have a price below 500. 56 00:02:40,470 --> 00:02:43,670 ‫And, the way it works is like this. 57 00:02:43,670 --> 00:02:48,670 ‫So, we always use db. The collection name .find. 58 00:02:49,170 --> 00:02:51,670 ‫And then, again, or filter object. 59 00:02:51,670 --> 00:02:54,620 ‫And so, remember, I want to search for prices, 60 00:02:54,620 --> 00:02:56,430 ‫so I say price. 61 00:02:56,430 --> 00:03:00,550 ‫And now, I want all the tours with a price below 500. 62 00:03:00,550 --> 00:03:02,090 ‫So, how do I do that? 63 00:03:02,090 --> 00:03:05,000 ‫Well, I need to use the less than operator 64 00:03:05,000 --> 00:03:06,630 ‫and it works like this. 65 00:03:06,630 --> 00:03:09,080 ‫We need to define yet a new object 66 00:03:09,080 --> 00:03:13,017 ‫where we set the lte property to 500, 67 00:03:15,090 --> 00:03:16,550 ‫then close that object, 68 00:03:16,550 --> 00:03:19,320 ‫and then close that first price object 69 00:03:19,320 --> 00:03:21,410 ‫and then close the function. 70 00:03:21,410 --> 00:03:23,950 ‫So, that looks very weird, I know, 71 00:03:23,950 --> 00:03:27,130 ‫but this is how we use query operators in MongoDB. 72 00:03:27,130 --> 00:03:30,200 ‫So, again, lte stands for less than 73 00:03:30,200 --> 00:03:32,070 ‫because that is what we're searching for. 74 00:03:32,070 --> 00:03:36,140 ‫Where the price is less than 500. 75 00:03:36,140 --> 00:03:38,820 ‫And, this special sign here is reserved in MongoDB 76 00:03:38,820 --> 00:03:40,490 ‫for its operators. 77 00:03:40,490 --> 00:03:43,520 ‫So, whenever you see this dollar sign here in MongoDB, 78 00:03:43,520 --> 00:03:45,933 ‫you know that it's a Mongo operator. 79 00:03:46,900 --> 00:03:48,690 ‫So, the weirdest part here is probably 80 00:03:48,690 --> 00:03:51,430 ‫that we have to do it inside a new object, 81 00:03:51,430 --> 00:03:54,600 ‫but if you think about it, it's actually really the only way 82 00:03:54,600 --> 00:03:58,430 ‫to specify that the price should not simply be 500, 83 00:03:58,430 --> 00:03:59,530 ‫but something else. 84 00:03:59,530 --> 00:04:03,320 ‫So, we have to set the price to something else than 500. 85 00:04:03,320 --> 00:04:04,760 ‫And, the best way really is 86 00:04:04,760 --> 00:04:06,870 ‫to just use another object in there. 87 00:04:06,870 --> 00:04:09,453 ‫So, that's exactly how MongoDB then works. 88 00:04:10,479 --> 00:04:13,280 ‫So, let's try this out now, hit return. 89 00:04:13,280 --> 00:04:15,600 ‫And, indeed, we get our two documents 90 00:04:15,600 --> 00:04:20,500 ‫where the price property is below 500. 91 00:04:20,500 --> 00:04:23,530 ‫Great, next up, let's actually search 92 00:04:23,530 --> 00:04:26,840 ‫for two search criteria at the same time. 93 00:04:26,840 --> 00:04:29,690 ‫So, what I want to do next is to search for documents 94 00:04:29,690 --> 00:04:32,910 ‫which have the price less or equal than 500, 95 00:04:32,910 --> 00:04:34,760 ‫which is what we had here already, 96 00:04:34,760 --> 00:04:37,910 ‫but also, at the same time, the rating greater 97 00:04:37,910 --> 00:04:39,903 ‫or equal to 4.8. 98 00:04:41,800 --> 00:04:46,040 ‫And so, that should then give us only this tour here. 99 00:04:46,040 --> 00:04:47,240 ‫So, only this one 100 00:04:47,240 --> 00:04:50,590 ‫because this is the only one which has the price below 500 101 00:04:50,590 --> 00:04:55,140 ‫and the rating equal or greater to 4.8. 102 00:04:55,140 --> 00:04:57,780 ‫So, it's 4.8 and so that one is the one 103 00:04:57,780 --> 00:05:00,150 ‫that should match our query. 104 00:05:00,150 --> 00:05:03,620 ‫So, let's clear it to take away some of the confusion. 105 00:05:03,620 --> 00:05:05,670 ‫Now, I want this result here 106 00:05:05,670 --> 00:05:08,550 ‫so that we can compare it with the next result. 107 00:05:08,550 --> 00:05:11,833 ‫And so, let's now write out the query that I just described. 108 00:05:13,710 --> 00:05:17,260 ‫So, find and, again, this one here is 109 00:05:17,260 --> 00:05:18,590 ‫gonna be just the same. 110 00:05:18,590 --> 00:05:22,690 ‫So, we want the price to be less or equal than 500. 111 00:05:22,690 --> 00:05:27,093 ‫Or, we could actually simply say less than 500. 112 00:05:28,630 --> 00:05:33,630 ‫So, lte is less than or equal and lt is simply less than. 113 00:05:35,690 --> 00:05:39,030 ‫So, this is the first part, the price less than 500. 114 00:05:39,030 --> 00:05:41,420 ‫And, at the same time, we want the rating 115 00:05:41,420 --> 00:05:43,003 ‫to be greater or equal to 4.8. 116 00:05:43,970 --> 00:05:44,980 ‫And, that's easy. 117 00:05:44,980 --> 00:05:47,900 ‫All we have to do is to specify a second field 118 00:05:47,900 --> 00:05:49,350 ‫in our filter object. 119 00:05:49,350 --> 00:05:51,823 ‫So, first, the price and now the rating. 120 00:05:53,330 --> 00:05:55,150 ‫So, we want the rating to be 121 00:05:56,340 --> 00:05:57,840 ‫and you can probably guess it, 122 00:05:58,880 --> 00:06:03,203 ‫greater than or equal 4.8. 123 00:06:05,080 --> 00:06:09,420 ‫Now, close this filter object and close the function. 124 00:06:09,420 --> 00:06:11,040 ‫So, let's test it out. 125 00:06:11,040 --> 00:06:14,360 ‫And, indeed, it gives us the result that we were expecting. 126 00:06:14,360 --> 00:06:18,520 ‫So, the only document where both the search criteria here 127 00:06:18,520 --> 00:06:20,840 ‫are true at the same time. 128 00:06:20,840 --> 00:06:23,310 ‫So, just to recap, when we want to search 129 00:06:23,310 --> 00:06:25,670 ‫for two criteria at the same time, 130 00:06:25,670 --> 00:06:28,540 ‫which basically is an and query, 131 00:06:28,540 --> 00:06:31,950 ‫so price less than 500, and rating greater 132 00:06:31,950 --> 00:06:32,953 ‫or equal to 4.8. 133 00:06:34,070 --> 00:06:36,000 ‫Well, the only thing that we have to do is 134 00:06:36,000 --> 00:06:39,080 ‫to specify two fields in the filter object. 135 00:06:39,080 --> 00:06:41,600 ‫And, I know this looks quite confusing. 136 00:06:41,600 --> 00:06:45,760 ‫I felt exactly the same when I was learning this stuff, 137 00:06:45,760 --> 00:06:47,800 ‫but I hope that you can still follow me 138 00:06:48,870 --> 00:06:53,790 ‫so that we can now actually take it even one level further. 139 00:06:53,790 --> 00:06:56,940 ‫So, here, we did an and query. 140 00:06:56,940 --> 00:07:00,100 ‫So, querying for documents where these two conditions 141 00:07:00,100 --> 00:07:03,820 ‫are both true, but now let's do an or query. 142 00:07:03,820 --> 00:07:06,470 ‫So, basically searching for all the documents 143 00:07:06,470 --> 00:07:09,070 ‫where either this part here is true 144 00:07:09,070 --> 00:07:11,103 ‫or this part is true. 145 00:07:13,350 --> 00:07:18,090 ‫So, db.tours.find 146 00:07:18,090 --> 00:07:20,050 ‫and let's close it here already 147 00:07:20,050 --> 00:07:22,653 ‫because this is gonna be an even more confusing one. 148 00:07:26,000 --> 00:07:29,410 ‫So, we want to do an or query and the way it works 149 00:07:29,410 --> 00:07:32,530 ‫with MongoDB operators is like this. 150 00:07:32,530 --> 00:07:37,530 ‫We say or and then here, we specify an array. 151 00:07:38,949 --> 00:07:42,520 ‫And, in this array, we will then put the two conditions 152 00:07:42,520 --> 00:07:45,003 ‫where we want one of them to be true. 153 00:07:46,714 --> 00:07:48,710 ‫So, again, I know this looks confusing, 154 00:07:48,710 --> 00:07:52,310 ‫but let's write it out now and I will then explain it again 155 00:07:52,310 --> 00:07:53,863 ‫when we're already doing that. 156 00:07:55,580 --> 00:07:59,220 ‫So, the first condition is the price should 157 00:07:59,220 --> 00:08:02,653 ‫be less than 500. 158 00:08:03,730 --> 00:08:05,823 ‫So, basically the same as before. 159 00:08:06,670 --> 00:08:08,623 ‫So, that is the first object. 160 00:08:09,600 --> 00:08:12,130 ‫So, all of this, so the first condition, 161 00:08:12,130 --> 00:08:14,040 ‫basically the first filter, 162 00:08:14,040 --> 00:08:15,240 ‫and then the second one. 163 00:08:16,990 --> 00:08:20,750 ‫So, the rating should be, just like before, 164 00:08:20,750 --> 00:08:25,750 ‫greater or equal than 4.8. 165 00:08:26,250 --> 00:08:28,513 ‫Close this one and close this one. 166 00:08:29,630 --> 00:08:31,800 ‫And so, that's actually already it. 167 00:08:31,800 --> 00:08:36,550 ‫So, again, to recap here, we start with the or operator 168 00:08:36,550 --> 00:08:40,030 ‫and the or operator accepts an array of conditions. 169 00:08:40,030 --> 00:08:43,150 ‫So, that's why we then create this array here 170 00:08:43,150 --> 00:08:45,610 ‫and this array will then contain one object 171 00:08:45,610 --> 00:08:48,470 ‫for each of our filters basically. 172 00:08:48,470 --> 00:08:51,650 ‫So, we want either this one to be true 173 00:08:51,650 --> 00:08:53,143 ‫or this one. 174 00:08:55,920 --> 00:09:00,130 ‫So, let's try to see what our results are gonna be. 175 00:09:00,130 --> 00:09:04,120 ‫And so, actually we get all of the three tours. 176 00:09:04,120 --> 00:09:06,357 ‫And so, let's analyze why that is. 177 00:09:06,357 --> 00:09:09,913 ‫So, the first one has a price less than 500. 178 00:09:11,260 --> 00:09:13,470 ‫And so, that's why it got included here. 179 00:09:13,470 --> 00:09:16,820 ‫It doesn't have the rating greater or equal to 4.8, 180 00:09:16,820 --> 00:09:20,940 ‫so it's just 4.7, but since we're doing an or query here, 181 00:09:20,940 --> 00:09:23,730 ‫only one of the conditions needs to be true. 182 00:09:23,730 --> 00:09:26,250 ‫And so, that's why this document here got selected 183 00:09:26,250 --> 00:09:28,180 ‫and is included in our output. 184 00:09:28,180 --> 00:09:32,940 ‫Next up, this one also has the price less or equal than 500 185 00:09:32,940 --> 00:09:35,800 ‫and also, at the same time, it has the rating great 186 00:09:35,800 --> 00:09:37,810 ‫or equal than 4.8. 187 00:09:37,810 --> 00:09:39,940 ‫And so, it got included actually 188 00:09:39,940 --> 00:09:41,623 ‫for both of them being true. 189 00:09:43,530 --> 00:09:47,980 ‫Then, the last one does not have the price less than 500, 190 00:09:47,980 --> 00:09:52,123 ‫but it does have the rating greater or equal to 4.8. 191 00:09:53,210 --> 00:09:56,210 ‫And so, again, one of the two conditions is true 192 00:09:56,210 --> 00:09:58,830 ‫and since we're doing an or query, 193 00:09:58,830 --> 00:10:00,483 ‫this tour also got included. 194 00:10:02,020 --> 00:10:04,080 ‫So, let's clear this and only one more, 195 00:10:04,080 --> 00:10:06,170 ‫which is gonna be kind of the same. 196 00:10:06,170 --> 00:10:11,080 ‫I'm simply gonna change from less than to greater than. 197 00:10:11,080 --> 00:10:12,630 ‫And, what I want you to do now is 198 00:10:12,630 --> 00:10:14,910 ‫to guess the output of this one based 199 00:10:14,910 --> 00:10:16,420 ‫on the previous result. 200 00:10:16,420 --> 00:10:18,820 ‫So, can you guess what the result will be? 201 00:10:18,820 --> 00:10:20,770 ‫So, let's take a look. 202 00:10:20,770 --> 00:10:24,490 ‫And so, now, indeed, we no longer have all three tours, 203 00:10:24,490 --> 00:10:26,750 ‫but only the second and the third one 204 00:10:26,750 --> 00:10:28,510 ‫because, remember, the first tour 205 00:10:28,510 --> 00:10:30,760 ‫had the price less than 500 206 00:10:30,760 --> 00:10:32,460 ‫and also the rating less than 4.8. 207 00:10:33,350 --> 00:10:35,820 ‫And so, none of the conditions were applying 208 00:10:35,820 --> 00:10:37,700 ‫and so it's no longer included. 209 00:10:37,700 --> 00:10:39,490 ‫Only the second and the third one, 210 00:10:39,490 --> 00:10:43,480 ‫which now has the price also not greater than 500, 211 00:10:43,480 --> 00:10:45,600 ‫but it has the rating of 4.8 212 00:10:45,600 --> 00:10:47,510 ‫and so it's still included. 213 00:10:47,510 --> 00:10:50,090 ‫And, the last one, of course, has everything true 214 00:10:50,090 --> 00:10:52,310 ‫and so, of course, it's also here. 215 00:10:52,310 --> 00:10:54,980 ‫Just one more thing that I wanted to show you here is 216 00:10:54,980 --> 00:10:58,290 ‫that besides our filter object, so this one, 217 00:10:58,290 --> 00:11:01,600 ‫we can also pass in an object for projection. 218 00:11:01,600 --> 00:11:04,610 ‫So, what projection means is that we simply want 219 00:11:04,610 --> 00:11:07,650 ‫to select some of the fields in the output. 220 00:11:07,650 --> 00:11:10,310 ‫So, let me show it to you and it's very simple. 221 00:11:10,310 --> 00:11:15,310 ‫All we have to do is, for example, say name equals to one. 222 00:11:15,510 --> 00:11:18,570 ‫So, what this means is that we only want the name 223 00:11:18,570 --> 00:11:22,670 ‫to be in the output and so that's why we set name to one. 224 00:11:22,670 --> 00:11:25,520 ‫All the others are not gonna appear in this case. 225 00:11:25,520 --> 00:11:26,780 ‫So, let me show that to you. 226 00:11:26,780 --> 00:11:28,770 ‫And, indeed, we only have the name 227 00:11:28,770 --> 00:11:30,870 ‫and no longer all these other properties. 228 00:11:30,870 --> 00:11:33,913 ‫And, this can be very useful in some cases. 229 00:11:35,130 --> 00:11:37,610 ‫The idea is, of course, also showing up, 230 00:11:37,610 --> 00:11:38,880 ‫but that's always there. 231 00:11:38,880 --> 00:11:41,300 ‫There's no way of removing that. 232 00:11:41,300 --> 00:11:42,780 ‫Okay, cool. 233 00:11:42,780 --> 00:11:46,460 ‫So, I think the main goal of this lecture is now achieved, 234 00:11:46,460 --> 00:11:48,450 ‫which was basically to get you familiar 235 00:11:48,450 --> 00:11:51,200 ‫with the way we query in MongoDB 236 00:11:51,200 --> 00:11:55,570 ‫and also show you these complex MongoDB operators 237 00:11:55,570 --> 00:11:57,090 ‫that we have here. 238 00:11:57,090 --> 00:11:58,590 ‫For some reason, I cannot select it, 239 00:11:58,590 --> 00:11:59,970 ‫but you know what I mean. 240 00:11:59,970 --> 00:12:01,540 ‫So, we have greater than, 241 00:12:01,540 --> 00:12:04,050 ‫we have or, and we really have a ton 242 00:12:04,050 --> 00:12:05,540 ‫of other operators still. 243 00:12:05,540 --> 00:12:07,360 ‫So, this is only the surface, 244 00:12:07,360 --> 00:12:09,960 ‫but throughout the rest of the course, you will, of course, 245 00:12:09,960 --> 00:12:12,990 ‫get to know a couple of other operators. 246 00:12:12,990 --> 00:12:15,260 ‫So, this is just to get you familiar, 247 00:12:15,260 --> 00:12:18,250 ‫get you started with querying in MongoDB. 248 00:12:18,250 --> 00:12:21,093 ‫And, I think in this lecture, we did that successfully.