WEBVTT 00:00.290 --> 00:00.770 Okay. 00:00.770 --> 00:05.960 What we have at the moment is an empty database, and we want to correct that and have some demo products 00:05.960 --> 00:11.390 so that we can lay out our user interface when it comes to building our client application, so on and 00:11.390 --> 00:12.080 so forth. 00:12.080 --> 00:13.310 So let's deal with that. 00:13.310 --> 00:19.310 Now let's close down this store and inside our data folder let's create another new class. 00:19.310 --> 00:30.290 So I'm going to say new file select class and we'll call it DB initial iser and press return okay. 00:30.320 --> 00:36.980 So in this class then we're going to create some code so that we can do something with our DB context, 00:36.980 --> 00:40.790 because we're going to need to save a bunch of products into our database. 00:40.790 --> 00:46.640 And where we're going to use this DB initializer class is actually in our program class. 00:46.640 --> 00:48.680 So we're going to do something inside here. 00:48.680 --> 00:53.360 And we're going to create a method inside here and say public void. 00:53.360 --> 00:57.500 Because after public comes what are we going to return from this method. 00:57.500 --> 00:59.480 Well, we're not going to return anything from it. 00:59.480 --> 01:01.520 And I'm going to call it init db. 01:01.910 --> 01:07.210 And in here we're going to pass in as a parameter web application app. 01:07.900 --> 01:14.650 And the reason for that, let's just open up the program class at the same time as we want access to 01:14.680 --> 01:16.870 this effectively. 01:16.870 --> 01:22.510 And I'll explain why as we build this particular class so that we can seed some data in there. 01:23.020 --> 01:26.170 So we're going to use something called a using statement here. 01:26.170 --> 01:30.070 And I'm going to say var scope using var scope equals app. 01:30.430 --> 01:33.040 And this will give us access to our services. 01:33.040 --> 01:35.200 And I can say create scope. 01:35.200 --> 01:39.940 So what's this using statement all about then if well if we hover over this then we can see that this 01:39.940 --> 01:41.530 has got a dispose method. 01:41.530 --> 01:47.230 And this performs application defined tasks associated with freeing, releasing or resetting unmanaged 01:47.230 --> 01:48.070 resources. 01:48.070 --> 01:54.790 So what this effectively does is anything that we use inside scope, the thing that we've called scope 01:54.790 --> 02:00.190 is going to be disposed of by the framework after we've finished using it. 02:00.220 --> 02:02.200 And we don't need to clean up ourselves. 02:02.200 --> 02:06.530 Now, dotnet is very good at cleaning up resources that are no longer in use. 02:06.680 --> 02:12.500 But by using this using statement, we ensure this happens as soon as it possibly can, rather than 02:12.530 --> 02:17.090 something called a garbage collector coming along at some future point which we do not have control 02:17.090 --> 02:17.720 over. 02:18.140 --> 02:23.120 It will clean up any unused resources, but this just guarantees that after we finished with this resource, 02:23.120 --> 02:25.730 it will be cleaned up on our behalf. 02:25.760 --> 02:31.670 Then I'm going to create a variable called context and say var context equals scope dot service provider. 02:31.730 --> 02:35.210 And we're going to say get required service. 02:35.210 --> 02:38.990 And I'm going to specify the store context. 02:38.990 --> 02:42.500 And this is going to give us access to our store context. 02:42.530 --> 02:45.530 Now we have to do this in a slightly different way. 02:46.040 --> 02:52.400 And because this is a service that's been defined in our program class in this code, then we need to 02:52.430 --> 02:58.640 get hold of that service via the framework, via the scope that we've been created or we have created 02:58.640 --> 02:59.570 up here. 03:00.050 --> 03:03.200 So this gives us access to our database context. 03:03.200 --> 03:08.290 And then I'm going to create a method called seed data and pass in the context. 03:08.530 --> 03:13.360 And if we hover over the context, then we can see that this is a type of store context. 03:13.360 --> 03:17.050 And it's got the optional property there. 03:17.050 --> 03:22.840 And that's not ideal because we don't want to try and use this if it could be null. 03:23.110 --> 03:27.430 So after the or instead of the semicolon here let's just go to the next line. 03:27.430 --> 03:29.050 We'll add a double question mark. 03:29.050 --> 03:35.470 And this tells dotnet what to do if the context is null. 03:35.800 --> 03:41.170 So if it is null then we're just going to throw a new exception and we'll just say throw new invalid 03:41.200 --> 03:46.240 operation exception because we cannot see data if we don't have our context. 03:46.240 --> 03:51.820 And I'm just going to say failed to retrieve store context. 03:51.820 --> 03:54.100 And then we've got our seed data method. 03:54.100 --> 03:55.120 Now this doesn't exist yet. 03:55.120 --> 04:01.480 So let's put our cursor inside seed data and use the quick fix to generate method seed data. 04:01.480 --> 04:07.300 And inside here, because we've now got access to our context, what we can do is we can migrate our 04:07.300 --> 04:11.030 database or update our database inside code. 04:11.030 --> 04:12.410 So I'm going to specify context. 04:12.410 --> 04:14.660 And then we've got access to our database. 04:14.660 --> 04:18.200 And we can use the migrate method. 04:18.200 --> 04:22.010 And if we hover over the migrate method then it tells us what it's going to do. 04:22.040 --> 04:26.330 This is going to apply any pending migrations fuller context to the database. 04:26.330 --> 04:30.200 And it will create a database if it does not already exist. 04:30.860 --> 04:34.910 So this will create and apply migrations to a database. 04:34.940 --> 04:40.130 Now we're also going to check to see if we have any products already in our database. 04:40.130 --> 04:46.190 So we'll add an if statement and we'll say if context dot products dot any, then we are simply going 04:46.190 --> 04:49.430 to return from this method and do nothing with it. 04:49.430 --> 04:56.240 So this return statement here, this is going to stop the execution of any more code inside this method. 04:56.840 --> 04:59.570 And below this we're going to create a new list of products. 04:59.570 --> 05:03.110 And we can say var products equals new list. 05:03.200 --> 05:06.350 And the list is going to be a type of product. 05:06.350 --> 05:10.640 And inside here we open curly brackets. 05:10.640 --> 05:11.860 So I'll go on to the next line. 05:11.890 --> 05:16.780 Open curly brackets and inside here we can start defining a new list of products. 05:16.810 --> 05:23.020 So I could say for instance, new products and then open curly brackets. 05:23.020 --> 05:25.930 And then I could start populating the different fields. 05:25.930 --> 05:28.780 So I could say id one, I need to be a comma. 05:28.780 --> 05:31.600 We could say the name equals test. 05:31.660 --> 05:36.670 We could say description equals whatever and carry on going like this. 05:36.670 --> 05:37.810 But we need a bunch of products. 05:37.810 --> 05:38.950 We don't just need one. 05:38.950 --> 05:44.320 And it's very tedious to start typing out all of this seed type of code. 05:44.320 --> 05:46.210 So we're not going to do that. 05:46.240 --> 05:52.630 I have provided a snippet for us to use that has a bunch of products that we can use for demonstration 05:52.630 --> 05:53.350 purposes. 05:53.350 --> 05:56.650 So let's go to the course assets folder. 05:56.650 --> 06:02.230 Please go back to lesson three if you haven't already got this, and make sure you download the course 06:02.260 --> 06:02.710 assets. 06:02.710 --> 06:07.060 Inside here is a file called products dot txt. 06:07.090 --> 06:11.410 If we open this then this just has a bunch of new products. 06:11.410 --> 06:17.960 And if I just control a control C and go back to VSCode and paste this in. 06:17.960 --> 06:25.550 And then just add the closing semicolon there and make sure things look okay. 06:25.580 --> 06:29.390 Then we can see that we have a bunch of new products. 06:29.390 --> 06:32.090 The formatting didn't work quite how I wanted it to. 06:32.120 --> 06:38.090 I'd like it to be shifted over slightly to the left, and the auto formatting, which we should be able 06:38.090 --> 06:42.860 to access via right clicking, and then just say format document. 06:42.860 --> 06:45.200 And there is a shortcut key for this as well. 06:45.230 --> 06:48.110 That should have shifted things over to the left a bit, but it didn't. 06:48.110 --> 06:49.640 So I'll just do that manually. 06:49.640 --> 06:52.280 And then we've got our bunch of new products inside here. 06:52.280 --> 06:56.960 Now there is a hint here about, hey, this could be simplified. 06:56.960 --> 07:02.750 And if we do take the opportunity to look at how it can be simplified, we can use the use new. 07:02.750 --> 07:05.060 And there's also a fix all here. 07:05.060 --> 07:08.990 So let's take a look at using that and say document. 07:09.290 --> 07:12.470 And this simplifies our code and takes out all of that new product. 07:12.470 --> 07:16.780 And this is something that was available in dotnet eight just to remove some of the boilerplate. 07:16.780 --> 07:20.140 That's not necessary when creating a new instance of something. 07:20.140 --> 07:23.500 So there's a slightly cleaner way to do this now. 07:23.500 --> 07:28.690 So our VAR products, we want to save this list of products into our database. 07:28.690 --> 07:35.350 So below the list of products let's bring the cursor down below that below the semicolon. 07:35.350 --> 07:43.210 And we'll say context dot products dot add range so that we add the range of products in that list. 07:43.210 --> 07:45.400 And we'll specify products. 07:45.790 --> 07:49.180 And then we'll say context and save changes. 07:49.210 --> 07:54.850 And the way that Entity Framework works is everything here and upwards. 07:54.850 --> 07:58.330 All it's doing is it's tracking this list of products in memory. 07:58.330 --> 08:04.930 And it's only when we get to the context save changes that we actually make a request to the database 08:04.930 --> 08:06.100 at this point. 08:06.100 --> 08:07.990 So that's our seed class. 08:07.990 --> 08:10.750 In the next lesson we'll take a look at how we can use this. 08:10.750 --> 08:16.000 And we'll seed the data into our database and we'll make sure it exists. 08:16.000 --> 08:18.160 And we'll take a look at that next.