WEBVTT 00:00.000 --> 00:00.270 Okay. 00:00.270 --> 00:08.520 Our next task is to create a web API controller that's going to be responsible for receiving HTTP requests, 00:08.940 --> 00:15.480 querying our database, and then returning the results in an HTTP response so that we can test this 00:15.480 --> 00:17.400 using our browser. 00:17.580 --> 00:25.380 So let's clean things up at the top and inside Solution Explorer inside the controllers folder. 00:25.380 --> 00:27.810 Let's go ahead and create a new file. 00:27.810 --> 00:30.750 And we do have a template for an API controller. 00:30.750 --> 00:33.660 So let's use this to see what it gives us. 00:33.660 --> 00:38.850 And we're going to call this products controller and press return. 00:38.850 --> 00:43.290 And this gives us the boilerplate for a typical API controller. 00:43.410 --> 00:49.350 And if we compare with an existing controller we have the demo one that was provided, the weather forecast 00:49.350 --> 00:49.800 controller. 00:49.800 --> 00:57.810 We can see that the start of the class resembles what we've just created via the template. 00:57.810 --> 01:00.430 We've got effectively a roots. 01:00.430 --> 01:07.960 How does Net know where to send the HTTP request that's coming in to the correct API controller? 01:08.350 --> 01:10.540 Well, it uses the routing system. 01:10.540 --> 01:18.490 So in order to access this controller we would need to use in our case https colon forward slash forward 01:18.490 --> 01:23.050 slash localhost colon 5001 forward slash API. 01:23.290 --> 01:25.030 And then this controller part. 01:25.060 --> 01:30.220 This is a placeholder for the name of the controller minus the word controller. 01:30.610 --> 01:36.670 So by convention this is if our API controller is called products controller. 01:36.670 --> 01:43.090 Then to access the endpoints in this controller we would use API forward slash products. 01:43.750 --> 01:46.720 Now this next attribute and these are known as attributes. 01:46.750 --> 01:50.530 These things in square brackets is API controller. 01:50.530 --> 01:57.190 And if we hover over this then this indicates that a type in all derived types are used to serve http, 01:57.220 --> 02:04.420 API responses and controllers decorated with this attribute are configured with features and behavior 02:04.450 --> 02:08.140 targeted at improving the developer experience. 02:08.140 --> 02:11.380 That's us for building APIs. 02:11.380 --> 02:12.790 So great. 02:12.790 --> 02:13.840 That's useful. 02:13.840 --> 02:19.870 And we won't talk about this now, but we'll take a look at some of its features a bit later on as we 02:19.870 --> 02:26.380 use some of its features, but it's not going to affect what we do in this controller at the moment. 02:26.380 --> 02:28.090 We'll just leave it in place. 02:28.360 --> 02:38.440 Now inside our API controllers, we create API endpoints and HTTP requests, use HTTP methods, things 02:38.440 --> 02:41.110 like an http get an http post. 02:41.110 --> 02:47.170 If we were going to create a resource, a get would be for a query for a resource, a put would be if 02:47.200 --> 02:49.810 we're updating a resource and delete. 02:49.840 --> 02:55.030 No prizes for guessing what that does, but it would delete a resource of course. 02:55.030 --> 03:01.190 So this one we're going to use the http get attribute, because we're going to get a list of our products 03:01.190 --> 03:02.480 from the database. 03:02.780 --> 03:09.410 Now we return a HTTP response from these HTTP endpoints. 03:09.410 --> 03:14.540 And the way that we do that in dotnet is we return an action result type. 03:14.540 --> 03:21.830 And we can specify what type of thing we're going to return in this result using the angle brackets. 03:21.830 --> 03:25.640 And we're going to return a list of products. 03:25.640 --> 03:30.590 And we need to bring in the using statement for where product has been defined. 03:30.620 --> 03:33.920 So we can where we've got the arrow, we can use our quick fix. 03:34.070 --> 03:38.510 And we can specify we want to use using API entities. 03:38.630 --> 03:41.270 And that gets added at the top here. 03:41.270 --> 03:44.600 So then we'll give the method a name. 03:44.600 --> 03:47.090 And we're going to call it Get products. 03:47.090 --> 03:51.980 And inside here we are going to return. 03:51.980 --> 03:58.600 And at this point we do need to inject our store context and the way that we inject. 03:58.600 --> 04:03.670 I'm just going to demonstrate two ways very quickly about how we inject something into our classes. 04:03.670 --> 04:11.230 There's the old fashioned way where we'd create a constructor using the snippet like so, and then we'd 04:11.230 --> 04:13.270 specify the thing that we want to inject. 04:13.270 --> 04:16.150 In this case, it's the store context, and we give it a name. 04:16.660 --> 04:24.250 And then what we would also do is we'd put our cursor inside context, and then we would use the create 04:24.250 --> 04:26.290 and assign field context. 04:26.290 --> 04:32.230 And this would create a private read only field that we can then access inside our method. 04:32.230 --> 04:33.550 Here I can say context. 04:33.550 --> 04:37.240 And this gives us access to Entity Framework queries. 04:37.240 --> 04:44.710 And it also populates the constructor and assigns the read only field context to list context which 04:44.710 --> 04:46.930 refers to list context. 04:46.930 --> 04:48.700 I'm highlighting here. 04:48.700 --> 04:52.870 So this context is effectively this. 04:52.870 --> 04:59.060 And then we're setting This context using this equals here. 04:59.060 --> 05:00.680 But there is a better way to do this. 05:00.680 --> 05:02.720 And we've got our ellipses here. 05:02.720 --> 05:06.680 So let's use the quick fix and we'll use the primary constructor. 05:07.280 --> 05:09.440 And then we've got access to our context. 05:09.440 --> 05:13.280 And there's no point in this read only line now so we can remove that. 05:13.280 --> 05:15.950 And now this gives us access to our context. 05:15.950 --> 05:18.470 And this is dependency injection. 05:19.100 --> 05:25.160 And when a new instance of our products controller is created which happens when it receives an HTTP 05:25.160 --> 05:30.050 request, then it instantiates a new instance of the store context. 05:30.080 --> 05:33.650 If we didn't define this as a service, then this would not work. 05:34.130 --> 05:37.880 But we have defined this as a service, so this should work. 05:37.910 --> 05:45.050 And then inside our Getproducts method we can return the context and products. 05:45.050 --> 05:47.870 And we can say to list. 05:47.870 --> 05:52.640 And this two list method is going to query our database. 05:52.640 --> 05:57.070 So all of the products in the database, we're going to output them to a list, and that's what we're 05:57.070 --> 05:59.110 going to return from this method. 05:59.200 --> 06:03.490 Let's create another method that will allow us to query for an individual product. 06:03.490 --> 06:05.470 So we're going to say Httpget. 06:05.710 --> 06:08.620 Then we'll add parentheses then quotes. 06:08.620 --> 06:16.150 And then in curly brackets we specify id and this is the ID of the product that we want to fetch from 06:16.150 --> 06:16.870 the database. 06:16.870 --> 06:18.280 And we'll use public. 06:18.400 --> 06:20.890 Again we'll use Actionresults. 06:20.890 --> 06:26.650 And this time we're just going to return a single product and we'll call it get product. 06:27.100 --> 06:31.780 And we need to specify the ID that we're receiving as a route parameter. 06:31.780 --> 06:39.370 So for list method it's going to be API forward slash products forward slash let's say two for instance. 06:39.370 --> 06:45.850 And this integer, the ID that we're passing in as a route parameter that's available here. 06:45.850 --> 06:49.450 We can pass as an argument to our get product method. 06:49.480 --> 06:53.640 Then inside here we can query our database. 06:53.640 --> 06:57.630 So I'm going to say var product equals context dot products. 06:57.630 --> 06:59.430 And then we've got a find method. 06:59.430 --> 07:02.670 And we can find a product that matches that ID. 07:03.510 --> 07:08.610 Now if we hover over the product at this point it will tell us what we're getting from our database 07:08.610 --> 07:10.620 and where we see that question mark. 07:10.620 --> 07:15.930 That means it could be a product, or it could be null, because our compiler doesn't know whether or 07:15.930 --> 07:18.330 not the product exists in our database. 07:18.330 --> 07:24.240 That matches the ID, because it also doesn't know what the ID that we're trying to look for at this 07:24.240 --> 07:25.020 point is. 07:25.020 --> 07:28.980 So it doesn't know if we're actually going to get a product back from the database. 07:28.980 --> 07:35.790 But if we take a look at the find method, then it finds an entity with the given primary key values 07:35.790 --> 07:37.950 and so on and so forth. 07:37.950 --> 07:41.280 But if no entity is found, then null is returned. 07:41.280 --> 07:43.680 So this could be a product or it could be null. 07:43.680 --> 07:46.860 And we need to check to see if that is indeed null. 07:46.860 --> 07:50.910 So we're going to check to see if the product is equal to null. 07:50.910 --> 07:53.120 And if it is we're going to return. 07:53.150 --> 08:00.260 And because we're in the context of an HTTP controller, we can return a not found which will result 08:00.260 --> 08:03.860 in a 404 not found being returned to the client. 08:03.890 --> 08:08.660 Then we can return the product, because at that point we know we have it. 08:08.690 --> 08:14.120 If we do comment out this line actually where we're returning not found, then we do get a warning to 08:14.150 --> 08:16.040 say, hey, product could be null here. 08:16.040 --> 08:23.060 So you do want to check for this, but if we put this line back in then the warning will go away. 08:23.630 --> 08:25.160 So that's our API controller. 08:25.160 --> 08:29.930 And if we go and test this in our browser right now, and let's go back to the tab with the weather 08:29.930 --> 08:30.530 forecast. 08:30.530 --> 08:35.960 And I swap weather forecast for API products and press return. 08:35.960 --> 08:37.670 Then I get an exception at the moment. 08:37.670 --> 08:44.930 And the reason for this, and this is very consistent, is that in when we add a new API controller, 08:44.930 --> 08:50.510 we always need to restart our API server before this is registered with our application. 08:50.540 --> 08:52.000 So let's go back to the terminal. 08:52.210 --> 08:55.300 And if I just scroll down, there's a couple of ways to do this. 08:55.330 --> 09:01.240 We can either use control and R, or we can use control C to stop our application. 09:01.240 --> 09:04.870 And then just use dotnet watch to restart it. 09:05.140 --> 09:08.530 And it does say there we can use control R to restart as well. 09:08.530 --> 09:11.260 So either approach will fix this. 09:11.260 --> 09:17.560 And if we go back to the browser and let's just make that request again, this time we can see that 09:17.560 --> 09:21.190 we're getting a list of products back from our database. 09:21.400 --> 09:27.610 And if I try and get an individual product, let's say product with the ID of three, then we get the 09:27.610 --> 09:32.140 product that matches that particular ID back from our database. 09:32.710 --> 09:33.640 Great. 09:33.640 --> 09:37.510 But we're not going to be using our browser to test our API functionality. 09:37.510 --> 09:42.730 It's fine just for a few get requests very quickly and easy to test, but there's a better tool that 09:42.730 --> 09:45.700 we're going to take a look at to make these API requests. 09:45.700 --> 09:48.370 And I want to introduce that in the next lesson. 09:48.370 --> 09:50.500 And we'll take a look at postman.