Breaking Apart Our Repository

Okay, we now have a repository, that's great, but 0:00 let's take another look at our design. 0:04 As we work on our project implementing this series and 0:07 artist controllers, we'll continue to add methods to our repository class. 0:10 Overtime, our repository can become bloated. 0:14 Also, our repository is currently concerned about persisting data for 0:18 more than one entity type, comic books and comic book artists. 0:22 We might think of our design is violating the single responsibility principle, 0:26 which states, that every class should have responsibility 0:30 over a single part of the functionality provided by your application. 0:34 Luckily for us, the solution to this problem is easy. 0:38 Instead of a single repository class, we can have multiple repository classes, 0:41 each focused on a single entity type. 0:47 Let's split out all of the repository methods that deal with comic books, 0:50 into its own repository class. 0:53 To start, let's add a class named ComicBooksRepository to the shared class 0:56 libraries date folder. 1:01 By default, classes use the internal access modifier, if one isn't specified. 1:02 That restricts access to this class to code within this project or assembly. 1:09 Adding a public access modifier, 1:14 will make this class accessible to code within the web app project. 1:15 Now, let's set up our database context instance. 1:19 At a private field of type Context named _context. 1:23 And a constructor that accepts a context instance, and 1:28 uses that the set the private field. 1:31 Remember, this is the same pattern that we used for the repository class, 1:38 which allows the controller to manage the lifetime of the context. 1:41 Now, we can select and cut the ComicBook related methods to the clipboard. 1:46 GetComicBooks, GetComicBook, AddComicBook, UpdateComicBook, 1:51 DeleteComicBook and ComicBookSeriesHasIssueNumber. 1:56 And paste those methods from the clipboard into the ComicBooksRepository class. 2:00 Let's also move over to ComicBookArtistRoleCombination method. 2:09 Looks like we've got some using directives to add. 2:27 For the namespaces, ComicBookShared.Models and 2:36 System.Data.Entity. 2:43 Now that we have a repository that's focused on comic books, 2:46 we can simplify our method names. 2:50 Consumers of this class will already know that they're working with comic books. 2:53 So we can remove any references to comic book from the method names. 2:57 For instance, we can change GetComicBooks to GetList, 3:01 And GetComicBook to simply Get. 3:10 And we can remove ComicBook from the CRUD method names. 3:13 For now, I'll leave the validation method names as they are. 3:32 Currently, we're instantiating an instance of the repository 3:36 in the BaseController class. 3:40 Doing this in the controller base class, 3:42 made the repository available to all of our controllers. 3:44 When you have a single repository class, this approach makes a lot of sense. 3:47 But when you have multiple focus repository classes, it's probably best to 3:52 allow each controller to instantiate the repositories that they need. 3:56 Given that, let's update the ComicBooksController to instantiate 4:01 an instance of our new ComicBooksRepository. 4:04 Add a private field for the repository. 4:07 And add a default constructor to instantiate an instance of the repository. 4:21 We need an instance of our database context to 4:34 pass into the ComicBooksRepository constructor. 4:37 In the BaseController class, the context is currently a private field. 4:40 We'll need to switch that over to be in a protected property, so 4:44 that it's accessible to the descendant controller classes. 4:48 And update any references to the private field to use the new property. 4:51 Back at the ComicBooksController, update the call to the ComicBooksRepository 5:02 constructor to pass in the base controller's context property. 5:06 Now we can update all of the bad repository references and method calls. 5:10 Repository.GetComicBooks becomes, 5:14 _comicBooksRepository, GetList. 5:19 Repository.GetComicBook becomes _comicBooksRepository get. 5:26 Repository.AddComicBook becomes _comicBooksRepository.Add. 5:39 Another call to Repository.GetComicBook to update. 5:45 Repository.UpdateComicBook becomes _comicBooksRepository.Update, 5:53 and another call to Repository.GetComicBook to update. 5:59 Repository.DeleteComicBook becomes _comicBooksRespository.Delete, 6:04 Repository.ComicBookSeriesHasIssueNumber becomes 6:11 _comicBookRepository.ComicBookSeriesHasIs- sueNumber. 6:16 And that fixes all of the build errors in the ComicBooksController. 6:21 Let's build the project by pressing Ctrl+Shift+B. 6:25 And the ComicBookArtistController has some build errors that we need to fix. 6:32 This controller will also need an instance on the ComicBook repository. 6:37 You might be tempted at this point to just move the ComicBooksRepository instance 6:41 into the BaseController. 6:46 But let's hold off on doing that. 6:47 I suspect that the series and 6:50 artist controllers won't need an instance of that repository. 6:51 So let's stick with our plan of letting each controller instantiate 6:55 the repositories that they need. 6:58 First, the private field. 7:01 Then, the default constructor. 7:11 And update the bad method calls 7:27 Repository.GetComicBook becomes 7:32 _comicBooksRepository.Get. 7:37 Once more, And 7:45 Repository.ComicBookHasArtistRoleCombina- tion 7:51 becomes _comicBook.Repository.ComicBookHasArtistR- 7:58 oleCombination. 8:07 And now the project is successfully building again. 8:11 In repository class, we have six methods left. 8:27 GetSeriesList, GetArtists, GetRoles, GetComicBookArtist, 8:33 AddComicBookArtist, and DeleteComicBookArtist. 8:39 Let's keep series, artist, and 8:44 role related methods in this class, at least for now. 8:46 Later on, when we have more than one method for 8:50 each of those entity types, we'll add a repository for those types. 8:52 But let's go ahead and 8:56 move the ComicBookArtist-related methods to a new repository class. 8:57 In fact, let's make that your next exercise. 9:02 Add a new repository class, move the GetComicBookArtist, 9:06 AddComicBookArtist, and DeleteComicBookArtist methods to it. 9:10 And update the ComicBookArtist controller as needed, 9:14 to get the project building again. 9:17 See you after the break. 9:20