1 00:00:00,480 --> 00:00:01,313 Memi: Okay, 2 00:00:01,313 --> 00:00:03,450 so, we've talked about API, 3 00:00:03,450 --> 00:00:05,460 about web APIs, 4 00:00:05,460 --> 00:00:07,470 we talked about the different types 5 00:00:07,470 --> 00:00:08,700 of web API, 6 00:00:08,700 --> 00:00:11,910 and now it's time for REST. 7 00:00:11,910 --> 00:00:14,463 So, what exactly is REST? 8 00:00:15,450 --> 00:00:16,560 As mentioned earlier, 9 00:00:16,560 --> 00:00:17,880 REST is an acronym, 10 00:00:17,880 --> 00:00:22,770 stands for "Representational State Transfer". 11 00:00:22,770 --> 00:00:24,030 Now at this point, 12 00:00:24,030 --> 00:00:25,650 you probably scratch your head 13 00:00:25,650 --> 00:00:26,917 and ask yourself, 14 00:00:26,917 --> 00:00:28,080 "What the?" 15 00:00:28,080 --> 00:00:30,510 Well, hell, yeah, 16 00:00:30,510 --> 00:00:31,470 I did it too, 17 00:00:31,470 --> 00:00:35,280 the first time I met this strange expression. 18 00:00:35,280 --> 00:00:36,840 But there is some logic in it, 19 00:00:36,840 --> 00:00:40,680 and here is an explanation in some simpler English. 20 00:00:40,680 --> 00:00:42,630 So what this definition means, 21 00:00:42,630 --> 00:00:44,283 is basically that, 22 00:00:45,120 --> 00:00:48,390 REST API enables transfer 23 00:00:48,390 --> 00:00:53,160 of representation of a resource's state. 24 00:00:53,160 --> 00:00:56,760 Now note, the utilized words; 25 00:00:56,760 --> 00:00:57,930 we are discussing here 26 00:00:57,930 --> 00:01:00,720 transfer of a 27 00:01:00,720 --> 00:01:04,290 representation of the state. 28 00:01:04,290 --> 00:01:06,483 And let's explain exactly what it means. 29 00:01:07,710 --> 00:01:11,160 Let's say, we have a client and a server; 30 00:01:11,160 --> 00:01:12,750 now as we mentioned before, 31 00:01:12,750 --> 00:01:15,060 REST, like similar web APIs, 32 00:01:15,060 --> 00:01:17,880 works in a request response model. 33 00:01:17,880 --> 00:01:20,187 So what happens is this, 34 00:01:20,187 --> 00:01:23,040 the client sends a request 35 00:01:23,040 --> 00:01:24,270 for the server, 36 00:01:24,270 --> 00:01:27,690 and asks for a resource's state. 37 00:01:27,690 --> 00:01:31,350 Now, let's understand what exactly a state is. 38 00:01:31,350 --> 00:01:33,210 So, we define state 39 00:01:33,210 --> 00:01:36,480 as the current resource properties, 40 00:01:36,480 --> 00:01:38,130 and or, 41 00:01:38,130 --> 00:01:41,283 the result of an action on the resource. 42 00:01:42,300 --> 00:01:43,350 So in our case, 43 00:01:43,350 --> 00:01:46,290 let's say that what we are looking for 44 00:01:46,290 --> 00:01:48,510 is order number 17. 45 00:01:48,510 --> 00:01:50,970 So we basically ask for the state 46 00:01:50,970 --> 00:01:52,920 of order number 17, 47 00:01:52,920 --> 00:01:56,250 which means we ask for the resource properties 48 00:01:56,250 --> 00:01:57,690 the order properties, 49 00:01:57,690 --> 00:02:00,090 such as when it was made, 50 00:02:00,090 --> 00:02:01,350 who is the user, 51 00:02:01,350 --> 00:02:04,290 what are the items in the order, and so on. 52 00:02:04,290 --> 00:02:07,263 So, this is the state of the order. 53 00:02:08,460 --> 00:02:10,830 What we get back from the server 54 00:02:10,830 --> 00:02:13,800 is a response containing the resource's 55 00:02:13,800 --> 00:02:16,440 state representation. 56 00:02:16,440 --> 00:02:20,040 So the server basically send us the resource, 57 00:02:20,040 --> 00:02:22,320 or the state of the resource, 58 00:02:22,320 --> 00:02:24,420 in some kind of representation. 59 00:02:24,420 --> 00:02:27,810 So the response represents the state, 60 00:02:27,810 --> 00:02:29,100 in some way, 61 00:02:29,100 --> 00:02:31,353 usually JSON, as we will see later. 62 00:02:33,060 --> 00:02:35,070 So, in our example, 63 00:02:35,070 --> 00:02:36,510 this is what we get; 64 00:02:36,510 --> 00:02:40,473 we get a representation of order number 17. 65 00:02:41,730 --> 00:02:43,480 Now, let's look at another example. 66 00:02:45,390 --> 00:02:48,750 Let's say, that the client sends a request 67 00:02:48,750 --> 00:02:50,760 to delete a resource. 68 00:02:50,760 --> 00:02:52,380 Before we asked to see, 69 00:02:52,380 --> 00:02:54,180 or to get the resource, 70 00:02:54,180 --> 00:02:56,850 now we ask to delete it. 71 00:02:56,850 --> 00:02:59,370 And what resource will you want to delete? 72 00:02:59,370 --> 00:03:03,000 We want to delete, again, order number 17. 73 00:03:03,000 --> 00:03:04,740 The server, this time, 74 00:03:04,740 --> 00:03:07,130 responds with, again, 75 00:03:07,130 --> 00:03:09,120 the resource's state representation 76 00:03:09,120 --> 00:03:11,130 which contains a status. 77 00:03:11,130 --> 00:03:12,843 And the status tells us 78 00:03:12,843 --> 00:03:16,110 that the resource has been actually deleted 79 00:03:16,110 --> 00:03:17,520 just like we asked for. 80 00:03:17,520 --> 00:03:20,850 So these are the basic components of REST; 81 00:03:20,850 --> 00:03:22,860 we see here is the resource, 82 00:03:22,860 --> 00:03:25,620 the state, and the transfer. 83 00:03:25,620 --> 00:03:29,160 The transfer is the transfer of the state's representation 84 00:03:29,160 --> 00:03:31,047 between the client and the server. 85 00:03:31,047 --> 00:03:33,290 The state of the current properties, 86 00:03:33,290 --> 00:03:36,327 or the current state of the resource, 87 00:03:36,327 --> 00:03:38,850 and the representation is the way 88 00:03:38,850 --> 00:03:41,130 the state is represented. 89 00:03:41,130 --> 00:03:43,680 Now, all this is quite theoretical, 90 00:03:43,680 --> 00:03:45,030 what happens in the real world, 91 00:03:45,030 --> 00:03:46,110 or in other word, 92 00:03:46,110 --> 00:03:48,510 what happens when we want to implement 93 00:03:48,510 --> 00:03:50,430 an actual REST API? 94 00:03:50,430 --> 00:03:52,527 So in this case, we will use, usually, 95 00:03:52,527 --> 00:03:54,270 the HTTP protocol. 96 00:03:54,270 --> 00:03:55,943 And, how will the request 97 00:03:55,943 --> 00:03:59,370 and the response look like using HTTP? 98 00:03:59,370 --> 00:04:02,220 Well, like this, 99 00:04:02,220 --> 00:04:04,147 the request will look something like, 100 00:04:04,147 --> 00:04:07,857 "GET/api/order/17" 101 00:04:07,857 --> 00:04:10,500 and the response is a number, 102 00:04:10,500 --> 00:04:13,650 in this case 200, and "OK", 103 00:04:13,650 --> 00:04:15,420 and some kind of JSON. 104 00:04:15,420 --> 00:04:16,829 Now, later in this course, 105 00:04:16,829 --> 00:04:19,380 we will deep dive into each component of the request, 106 00:04:19,380 --> 00:04:20,213 and the response. 107 00:04:20,213 --> 00:04:21,046 So, don't worry 108 00:04:21,046 --> 00:04:24,180 if you don't understand exactly what is going on here, 109 00:04:24,180 --> 00:04:25,230 but suffice to say, 110 00:04:25,230 --> 00:04:28,140 that this is a general representation 111 00:04:28,140 --> 00:04:30,180 of the request and the response, 112 00:04:30,180 --> 00:04:32,250 over the HTTP protocol. 113 00:04:32,250 --> 00:04:33,930 And now, let's deep dive 114 00:04:33,930 --> 00:04:37,260 into how a request and the response look like, 115 00:04:37,260 --> 00:04:38,133 in REST.