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Let's start with reviewing the comic books controller—specifically the `Index`, `Detail`, and `Add` action methods—and put together our plan for updating the action methods to use EF to retrieve data from the database.
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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/v1.5 -b preparing-our-plan
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[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
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