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You have completed Entity Framework with ASP.NET MVC!
You have completed Entity Framework with ASP.NET MVC!
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Instead of a single repository class we can have multiple repository classes, each focused on a single entity type. Let's start by splitting out all of the repository methods that deal with comic books into its own repository class.
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To follow along committing your changes to this course, you'll need to fork the dotnet-comic-book-library-manager repo. Then you can clone, commit, and push your changes to your fork like this:
git clone <your-fork>
cd dotnet-comic-book-library-manager
git checkout tags/v3.3 -b breaking-apart-our-repository
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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
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