1 00:00:03,810 --> 00:00:05,895 In the previous lecture, 2 00:00:05,895 --> 00:00:07,880 we learned about REST API. 3 00:00:07,880 --> 00:00:10,781 You have seen how the REST API endpoints 4 00:00:10,781 --> 00:00:14,990 support a way for a client application to be able to either retrieve 5 00:00:14,990 --> 00:00:23,100 data from the server or upload data to the server using the various HTTP operations. 6 00:00:23,100 --> 00:00:27,062 In this lecture and exercise that follows this lecture, 7 00:00:27,062 --> 00:00:30,985 we'll look specifically about what kind of support Express 8 00:00:30,985 --> 00:00:36,545 supports for designing and implementing a REST API-based server. 9 00:00:36,545 --> 00:00:40,085 In particular, we'll also look at the Express router, 10 00:00:40,085 --> 00:00:44,600 and how it enables us to subdivide our application and 11 00:00:44,600 --> 00:00:50,285 then organize it into multiple mini Express-like applications, 12 00:00:50,285 --> 00:00:54,495 which combine together to form the Express application, 13 00:00:54,495 --> 00:01:00,605 specifically when we are dealing with various REST API and parts. 14 00:01:00,605 --> 00:01:02,985 So to summarize, in the previous lecture, 15 00:01:02,985 --> 00:01:06,315 we examined REST in detail. 16 00:01:06,315 --> 00:01:10,560 We also looked at how each endpoint is identified by a URI, 17 00:01:10,560 --> 00:01:13,950 and how we can specify the various operations to be done on 18 00:01:13,950 --> 00:01:18,295 each endpoint using the appropriate HTTP verb, 19 00:01:18,295 --> 00:01:20,880 the GET, PUT, POST, or DELETE. 20 00:01:20,880 --> 00:01:22,560 Now in this lecture, 21 00:01:22,560 --> 00:01:29,530 we'll look at how Express supports the development of a REST API server. 22 00:01:29,530 --> 00:01:35,070 We'll look at Express's support for various matters like app.all, 23 00:01:35,070 --> 00:01:38,335 app.get, put, post, and delete, 24 00:01:38,335 --> 00:01:43,305 and how these methods can be used to construct a REST API server. 25 00:01:43,305 --> 00:01:50,104 Within Express, the various application groups can be defined using the, app. 26 00:01:50,104 --> 00:01:51,955 and the various methods. 27 00:01:51,955 --> 00:01:59,180 So, the app.all specifies an operation that needs to be done on all the various verbs, 28 00:01:59,180 --> 00:02:00,990 on, in, and part. 29 00:02:00,990 --> 00:02:04,050 So for example, in this example, 30 00:02:04,050 --> 00:02:07,970 we see that the endpoint is defined by /dishes, 31 00:02:07,970 --> 00:02:13,230 and so the app.all, whatever is specified in the function that is given for app.all, 32 00:02:13,230 --> 00:02:16,830 will be applied to all the incoming requests. 33 00:02:16,830 --> 00:02:22,155 The app.get specifies what needs to be done for GET requests and, 34 00:02:22,155 --> 00:02:24,233 correspondingly, for the POST, 35 00:02:24,233 --> 00:02:30,015 PUT, and DELETE requests which are sent to the /dishes endpoint, 36 00:02:30,015 --> 00:02:32,700 as shown in this example. 37 00:02:32,700 --> 00:02:39,471 Express also supports defining the endpoints with parameters. 38 00:02:39,471 --> 00:02:45,750 So for example, you can specify a specific dish ID if you wish to, 39 00:02:45,750 --> 00:02:49,500 and then let the operation be performed for 40 00:02:49,500 --> 00:02:55,320 that specific endpoint referring to that specific dish with a given dish ID. 41 00:02:55,320 --> 00:02:58,890 So in this case, the dish ID itself is 42 00:02:58,890 --> 00:03:03,706 specified as a parameter and the pattern used for that is, 43 00:03:03,706 --> 00:03:05,460 as you see in this example, 44 00:03:05,460 --> 00:03:11,920 /dishes/: and then you would specify the parameter here. 45 00:03:11,920 --> 00:03:14,310 To make it easy for us to understand, 46 00:03:14,310 --> 00:03:18,060 I named the parameter as dishId in there. 47 00:03:18,060 --> 00:03:22,035 You can use any parameter name that you choose to, but again, 48 00:03:22,035 --> 00:03:27,290 using a meaningful name for a parameter makes it more easier to understand the code. 49 00:03:27,290 --> 00:03:28,815 So in this example, 50 00:03:28,815 --> 00:03:34,058 the :dishId means that if we issue a request to an endpoint, 51 00:03:34,058 --> 00:03:38,400 say for example, /dishes/23, 52 00:03:38,400 --> 00:03:45,300 then the dishId parameter enables us to extract this number 23 so that we 53 00:03:45,300 --> 00:03:48,420 can operate on dish number 23 within 54 00:03:48,420 --> 00:03:52,496 the function that is specified inside this method here. 55 00:03:52,496 --> 00:03:55,190 So in there, the parameter, 56 00:03:55,190 --> 00:04:01,440 the dishId parameter itself can be obtained by using the request object on which 57 00:04:01,440 --> 00:04:04,020 the params property you supported and 58 00:04:04,020 --> 00:04:08,885 the params property supports all the incoming request parameters, 59 00:04:08,885 --> 00:04:10,470 and dishId, in particular, 60 00:04:10,470 --> 00:04:13,710 is one of those request parameters which can be accessed, 61 00:04:13,710 --> 00:04:16,271 as shown in the code here. 62 00:04:16,271 --> 00:04:22,585 When you send a PUT or a POST request from the client to the server, 63 00:04:22,585 --> 00:04:28,545 you're often enclosing the data in the body of the message that is sent to the server. 64 00:04:28,545 --> 00:04:31,110 Now, which means that we need a method 65 00:04:31,110 --> 00:04:34,230 of extracting information from the body of the message. 66 00:04:34,230 --> 00:04:39,320 So this is where the body parser middleware for Express is very useful. 67 00:04:39,320 --> 00:04:44,805 So the body parser enables us to parse the information from the body of the message. 68 00:04:44,805 --> 00:04:47,515 To use the body parser, as we would expect, 69 00:04:47,515 --> 00:04:52,155 we would install the body-parser node module, 70 00:04:52,155 --> 00:04:56,070 and then require it within our Express application, 71 00:04:56,070 --> 00:04:59,550 and then specify app.use(bodyParser). 72 00:04:59,550 --> 00:05:03,570 And if the body contains data in the JSON format, 73 00:05:03,570 --> 00:05:05,810 you can say bodyParser.json, 74 00:05:05,810 --> 00:05:09,561 so which means that this will parse only data that is in 75 00:05:09,561 --> 00:05:14,250 JSON format that is enclosed in the body of that request message. 76 00:05:14,250 --> 00:05:16,145 In particular, in the exercise, 77 00:05:16,145 --> 00:05:22,620 we will be parsing incoming data which is sent in the form of a JSON string. 78 00:05:22,620 --> 00:05:24,930 The body parser, as you would expect, 79 00:05:24,930 --> 00:05:30,480 parses the body of the message and populates the req.body property. 80 00:05:30,480 --> 00:05:32,190 So, on the request, 81 00:05:32,190 --> 00:05:36,250 the body property will contain whatever is parsed in from 82 00:05:36,250 --> 00:05:41,600 the body of the request message by body parser. 83 00:05:41,600 --> 00:05:45,030 If you are implementing an Express application 84 00:05:45,030 --> 00:05:48,465 which supports multiple REST API endpoints, 85 00:05:48,465 --> 00:05:53,265 then it makes sense to subdivide the code into 86 00:05:53,265 --> 00:05:59,520 multiple modules and then make use of them to construct the overall Express application. 87 00:05:59,520 --> 00:06:03,347 So this where the Express router comes to our aid. 88 00:06:03,347 --> 00:06:08,070 An Express router defines many Express application, 89 00:06:08,070 --> 00:06:10,045 and within that many Express application, 90 00:06:10,045 --> 00:06:11,480 you can, for example, 91 00:06:11,480 --> 00:06:16,550 deal with one particular REST API endpoint in more detail, 92 00:06:16,550 --> 00:06:20,215 or one particular pattern of REST API endpoint in more detail. 93 00:06:20,215 --> 00:06:27,656 So, for example, we can define a dishRouter as express.Router, 94 00:06:27,656 --> 00:06:32,450 and then the dishRouter can then handle the endpoints. 95 00:06:32,450 --> 00:06:35,420 So when you express something as express.Router, 96 00:06:35,420 --> 00:06:38,570 it supports the route endpoint. 97 00:06:38,570 --> 00:06:41,015 One of the reasons for using Express router, 98 00:06:41,015 --> 00:06:42,455 as you would realize, 99 00:06:42,455 --> 00:06:45,470 is that if we use the standard app GET, 100 00:06:45,470 --> 00:06:47,142 PUT, POST, and DELETE methods, 101 00:06:47,142 --> 00:06:48,760 for each one of these methods, 102 00:06:48,760 --> 00:06:52,315 you need to explicitly specify the REST API endpoints. 103 00:06:52,315 --> 00:06:55,130 One advantage of using Express router is that if you 104 00:06:55,130 --> 00:06:59,422 say the router.Route and then specify the endpoint, 105 00:06:59,422 --> 00:07:07,220 that endpoint will be applied to all the methods and all the various GET, PUT, POST, 106 00:07:07,220 --> 00:07:11,060 and DELETE verb-related methods can all be chained 107 00:07:11,060 --> 00:07:16,575 together into the route in defining the code for our application. 108 00:07:16,575 --> 00:07:22,075 We'll look at more details of this in the exercise that follows this lecture. 109 00:07:22,075 --> 00:07:27,505 With this quick understanding of how Express supports REST API endpoint, 110 00:07:27,505 --> 00:07:31,070 let's move on to the exercise where we will construct 111 00:07:31,070 --> 00:07:35,682 their support for the /dishes REST API endpoint. 112 00:07:35,682 --> 00:07:38,180 As part of the first assignment, 113 00:07:38,180 --> 00:07:40,160 you will be further extending 114 00:07:40,160 --> 00:07:44,559 this Express application to support additional REST API endpoints, 115 00:07:44,559 --> 00:07:48,990 including /promotions and /leaders. 116 00:07:48,990 --> 00:07:52,040 If you have taken the previous courses in the specialization, 117 00:07:52,040 --> 00:07:55,220 you will immediately begin to see why we are supporting 118 00:07:55,220 --> 00:08:00,810 all these different REST API endpoints on other server side.