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Let's add a repository to our web app project.
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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/v3.2 -b using-the-repository-pattern
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CTRL+SHIFT+B- Build Solution
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So far in this course,
0:00
we've been using the database
context directly in our controllers.
0:01
This can lead to code duplications
not only across controllers but
0:05
also across applications,
0:09
violating the design principle called DRY,
Don't Repeat Yourself.
0:11
The comic book library management
console app used a repository But
0:16
its overall design,
as we saw earlier in this course,
0:20
wasn't going to work
well with our web app.
0:23
Given that, we decided to hold off on
using a repository, at least initially.
0:25
Now that we've fully implemented
two of our web apps for
0:31
controllers, it's time to revisit
the repository design pattern.
0:34
We can think of the repository as
a central location for storing and
0:38
managing entities.
0:42
Whenever we need to retrieve entities
from the data base or add, update or
0:44
delete an entity we call
a method on the repository class
0:49
instead of using the data
base context directly.
0:52
With this design,
only the repository class has knowledge
0:56
of the context class when
working with entities.
0:59
This approach makes it simple for the rest
of the app to retrieve and persist data.
1:02
Let's add a repository
to our web app project.
1:08
Since we aren't planning on using
the existing repository class
1:11
in our web app project Let's
do a little house cleaning and
1:14
move the existing repository
back to the console app project.
1:18
Add a data folder to
the console app project and
1:22
drag and drop the Repository.cs file from
the shared class library projects data
1:28
folder to the console app
projects data folder.
1:32
Then delete the file in
the shared class library project.
1:36
Now we have some name spaces to fix.
1:40
Change the repository classes name
space from comic book shared data
1:42
to comic book library manager data.
1:47
And add a using directive for
the comic book shared data name space.
1:50
And finally, in the program.cs file,
change the ComicBookShared.Data name space
1:55
to ComicBookLibrary.Data.
2:00
Now, let's add our new repository class.
2:09
We could add a repository class within
a data folder in the web app project.
2:12
That matched what we did
in the console lab project.
2:17
But I am going to go ahead and
2:20
add our new repository class in the shared
class library project's data folder.
2:21
Putting our repository in the shared
class library will give us the option to
2:26
update the console lab project
to use the new repository.
2:30
Or we might add another project to
the solution at some point in the future.
2:34
Maybe a public facing website or
a web based API project.
2:38
Either of which might be able
to use the new repository.
2:43
In order to make this class
accessible to the web app project,
2:46
we need to add a public access modifier.
2:49
Unlike the console apps repository,
which instantiates its own instances
2:51
of the database context We'll add a single
constructor to our new repository, which
2:56
will require the consumer of this class
to provide an instance of the context.
3:00
First, the private field,
private Context _context = null
3:05
Then the constructor public
Repository(Context context).
3:14
_context=context.
3:24
Doing this will allow our web apps
controllers to continue to control
3:28
the context's lifetime.
3:31
Let's turn our attention
to our base controller.
3:33
Now that our controllers will use the repository for all data retrieval and
3:36
persistance.
3:40
We can convert the context
property back to a private field.
3:41
Private context underscore
context equals null.
3:46
Then change the context property
to be a repository property.
3:51
Change the type to repository and
3:55
the name to repository, and
update the default constructor.
3:59
Context is now underscore context, and
initialize the repository property.
4:06
Passing in the context private field.
4:16
Don't forget to change the context
property reference in the dispose method
4:19
to use the context field.
4:23
Press control Shift B to build Okay,
4:27
after making these changes, we've introduced a whole slew of build errors.
4:32
To resolve these errors,
we'll need to move
4:36
all of our database context queries and
commands to our new repository class.
4:39
Let's start with updating the comic books controller's index action method.
4:44
Copy the link word to the clipboard and
switch back to the repository class.
4:48
In the repository class,
4:53
add a getComicBooks method that returns
an I list of comic book entities.
4:54
Public IList comic book
at a using directive for
4:59
the comic book shared model's name space,
then the method name, getComicBooks.
5:05
Now, paste the query from the clipboard
into this method, add the return keyword,
5:13
and change context to underscore context.
5:19
Don't forget to add a using directive for
the system data entity namespace so
5:25
we can use the include method
to eagerly load related entity.
5:30
Every method that we add to the repository
class will return a collection of
5:36
entities, a single entity,
a value type like a Boolean value, or
5:40
void if a return value isn't needed.
5:45
Notice that we're calling ToList
to force execution of the query.
5:47
Forcing execution of the query allows
us to return a list collection type,
5:51
like I list of t.
5:56
it makes it clear that the database
query will happen here in this method.
5:58
I find this approach to be cleaner and
6:02
simpler to returning an I-queriable
object from the repository.
6:05
Back in the controller, update the index
action method to use the repository class
6:12
method that we just added.
6:17
Repository Get ComicBooks.
6:18
One error down 24 left to fix.
6:22
This is our next exercise.
6:26
Go ahead and
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fix the remaining errors by adding new methods to the repository class.
6:29
If you get stuck don't worry.
6:33
In the next video I'll look
at how I resolved each error.
6:35
Good luck and we'll see you in a bit.
6:38
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