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So far in this course,

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we've been using the database
context directly in our controllers.

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This can lead to code duplications
not only across controllers but

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also across applications,

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violating the design principle called DRY,
Don't Repeat Yourself.

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The comic book library management
console app used a repository But

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its overall design,
as we saw earlier in this course,

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wasn't going to work
well with our web app.

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Given that, we decided to hold off on
using a repository, at least initially.

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Now that we've fully implemented
two of our web apps for

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controllers, it's time to revisit
the repository design pattern.

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We can think of the repository as
a central location for storing and

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managing entities.

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Whenever we need to retrieve entities
from the data base or add, update or

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delete an entity we call
a method on the repository class

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instead of using the data
base context directly.

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With this design,
only the repository class has knowledge

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of the context class when
working with entities.

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This approach makes it simple for the rest
of the app to retrieve and persist data.

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Let's add a repository
to our web app project.

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Since we aren't planning on using
the existing repository class

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in our web app project Let's
do a little house cleaning and

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move the existing repository
back to the console app project.

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Add a data folder to
the console app project and

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drag and drop the Repository.cs file from
the shared class library projects data

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folder to the console app
projects data folder.

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Then delete the file in
the shared class library project.

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Now we have some name spaces to fix.

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Change the repository classes name
space from comic book shared data

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to comic book library manager data.

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And add a using directive for
the comic book shared data name space.

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And finally, in the program.cs file,
change the ComicBookShared.Data name space

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to ComicBookLibrary.Data.

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Now, let's add our new repository class.

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We could add a repository class within
a data folder in the web app project.

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That matched what we did
in the console lab project.

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But I am going to go ahead and

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add our new repository class in the shared
class library project's data folder.

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Putting our repository in the shared
class library will give us the option to

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update the console lab project
to use the new repository.

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Or we might add another project to
the solution at some point in the future.

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Maybe a public facing website or
a web based API project.

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Either of which might be able
to use the new repository.

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In order to make this class
accessible to the web app project,

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we need to add a public access modifier.

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Unlike the console apps repository,
which instantiates its own instances

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of the database context We'll add a single
constructor to our new repository, which

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will require the consumer of this class
to provide an instance of the context.

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First, the private field,
private Context _context = null

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Then the constructor public
Repository(Context context).

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_context=context.

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Doing this will allow our web apps
controllers to continue to control

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the context's lifetime.

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Let's turn our attention
to our base controller.

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Now that our controllers will use the repository for all data retrieval and

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persistance.

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We can convert the context
property back to a private field.

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Private context underscore
context equals null.

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Then change the context property
to be a repository property.

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Change the type to repository and

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the name to repository, and
update the default constructor.

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Context is now underscore context, and
initialize the repository property.

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Passing in the context private field.

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Don't forget to change the context
property reference in the dispose method

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to use the context field.

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Press control Shift B to build Okay,

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after making these changes, we've introduced a whole slew of build errors.

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To resolve these errors,
we'll need to move

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all of our database context queries and
commands to our new repository class.

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Let's start with updating the comic books controller's index action method.

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Copy the link word to the clipboard and
switch back to the repository class.

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In the repository class,

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add a getComicBooks method that returns
an I list of comic book entities.

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Public IList comic book
at a using directive for

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the comic book shared model's name space,
then the method name, getComicBooks.

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Now, paste the query from the clipboard
into this method, add the return keyword,

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and change context to underscore context.

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Don't forget to add a using directive for
the system data entity namespace so

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we can use the include method
to eagerly load related entity.

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Every method that we add to the repository
class will return a collection of

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entities, a single entity,
a value type like a Boolean value, or

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void if a return value isn't needed.

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Notice that we're calling ToList
to force execution of the query.

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Forcing execution of the query allows
us to return a list collection type,

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like I list of t.

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it makes it clear that the database
query will happen here in this method.

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I find this approach to be cleaner and

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simpler to returning an I-queriable
object from the repository.

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Back in the controller, update the index
action method to use the repository class

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method that we just added.

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Repository Get ComicBooks.

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One error down 24 left to fix.

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This is our next exercise.

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Go ahead and

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fix the remaining errors by adding new methods to the repository class.

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If you get stuck don't worry.

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In the next video I'll look
at how I resolved each error.

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Good luck and we'll see you in a bit.