Preparing Our Plan

[MUSIC] 0:00 Welcome back. 0:04 In this section we will be updating our web app to retrieve and 0:06 process Comic book data from and to the database. 0:09 As we do that, we'll look at how to configure the context 0:12 database connection string, set the database initializer, 0:15 manage the lifetime of the database context, and more. 0:19 Are you ready to start updating our web app to use EF? 0:22 Let's get started. 0:25 The Comic Book Library Manager Web App has three top level sections. 0:27 Comic Books, Series, and Artists. 0:31 Any of these sections could be used as a starting point for 0:35 adding EF to our web app. 0:38 But let's start with the comic books section, 0:39 that will give us a good jumping off point into our web app. 0:42 It's the heart of our app, and it has enough meat on the bones, so to speak, 0:45 to give us a realistic example. 0:50 We'll start with updating the ComicBooksController, 0:55 specifically the index. 0:58 Detail and Add action methods. 1:02 Each place in the controller class that we need to update 1:09 is marked with a TODO code comment. 1:12 The Index action method needs a query that returns a list of comic books. 1:14 The detailAction method needs a query that returns a single comic book. 1:19 And in the addAction method, the viewModelsInit method 1:28 Needs to query a list of the artists and roles. 1:35 And in the base class, a list of series. 1:43 When we move the EF related classes out of the console lib project, the class library 1:47 project, one of the classes that we moved was a repository class. 1:52 Let's review the contents of that class. 1:57 Press Ctrl+m, Ctrl+o to collapse the class down to its definitions. 1:59 That'll make it easier to see all of the methods in the class at a glance. 2:05 Placing your cursor on a collapsed section and 2:09 pressing Ctrl+m, Ctrl+m will expand that section. 2:12 Pressing Ctrl+m, Ctrl+m a second time will collapse that section again. 2:15 The GetContext() method is responsible for creating an instance of the context class. 2:21 Other methods in this class, 2:26 as we'll see in the next method, call this method to get an instance of the context. 2:28 Notice that the Database.Log property is being set to a simple Lambda expression 2:32 that uses the Debug.WriteLine method to log messages. 2:37 The GetComicBooks method returns a list of comic books. 2:41 And it eagerly loads the related series entity by 2:45 including the series navigation property. 2:48 The GetComicBook method returns a single comic book with the series and 2:55 artists related entities eagerly loaded. 3:00 And a bit further down, here are methods that 3:04 return lists of Series, Artists and Roles. 3:09 Each of this lists is needed by the view model for the AddComicBook page. 3:14 So to recap, the repository class has a method to complete every one 3:19 of the TODOs in the index, detail and add action methods. 3:23 That's great. 3:29 What's not so great is that each method in the repository class 3:30 instantiates it's own instance of the context class. 3:34 Why is this a problem? 3:38 Let's look at an example. 3:40 The addAction method will need to call the GetSeries, GetArtists, 3:47 and GetRoles methods on the repository class in order to get the series, 3:53 artist, and roles data. 3:58 If we expand those methods, we can see that each method makes a call 4:02 to the GetContext() Method, wrapped in a using () statement. 4:06 So three instances of the context class will get instantiated. 4:10 Ideally, each of these queries would use the same context class, especially when 4:14 they're being called from within the same invocation of the add action method. 4:19 In the next section, we'll create an improved version of our repository 4:24 that'll work better with our MVC web app. 4:28 For now, we'll just copy the link queries that we need from the repository class 4:31 to our controller action methods. 4:36 But before we do that, there is some prep work that we need to do. 4:38 Two things are needed in order to ensure that EF is 4:42 properly configured for a web app. 4:45 Configure the server and 4:47 database that EF should use and configure the database initializer. 4:48 We'll start with configuring the server and database. 4:54 There are a number of ways to accomplish this. 4:57 Do you recall the method that allows you to specify the server and 4:59 database via configuration? 5:03 In the next video we'll start with making that change to our web app. 5:06