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Let's update the "Program.cs" file to use our context class to add a comic book, retrieve a list of comic books, and write the comic book series titles to the console.
Follow Along
To follow along commiting your changes to this course, you'll need to fork the dotnet-comic-book-gallery-model repo. Then you can clone, commit, and push your changes to your fork like this:
git clone <your-fork>
cd dotnet-comic-book-gallery-model
git checkout tags/v1.7 -b using-the-context
Additional Learning
Keyboard Shortcuts
-
F12- Go To Definition -
ALT+F12- Peek Definition
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Let's update the program.CS file to use
our context class to add a comic book,
0:00
retrieve a list of comic books, and
0:06
write the comic book series
titles to the console.
0:08
To start, we need to instantiate
an instance of our context class.
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Var context = new context.
0:15
If we press F12, to look at
the definition of our context class,
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and F12 again to look at the definition
for the DbContext class,
0:26
we can see that the DbContext,
implements the IDisposable interface.
0:32
Press Alt, F12 to peak the definition for
the IDisposable interface.
0:37
The i-disposable interface
provides a mechanism for
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releasing unmanaged resources through
its single method dispose unmanaged
0:45
resources need to be released or cleaned
up in order to prevent memory leaks.
0:51
Applications that have memory leaks will
gradually over time consume more and
0:56
more memory which will cause
the application to slow down.
1:00
And potentially even slow down the machine
that the application is hosted on.
1:03
When we use our contacts to persist,
or retrieve data from the database,
1:10
EF will open a connection to the database,
which is an unmanaged resource.
1:14
By calling our context's dispose method,
which is inherited from the DB context
1:19
base class, we're letting EF know that
the database connection can be closed.
1:24
We can easily ensure that
the context is dispose method will
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be called by placing the instantiation
of the context within a using statement.
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Using open parenthesis close parenthesis
and then a set curly braces.
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Now we can use the context to add
a comic book to the database.
1:50
To start we need to call the add method
on the context as comic books DB set
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property.
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And pass in an instance
of the comic book model.
1:59
Context.ComicBooks.Add(new ComicBook).
2:02
Don't forget to add the using directive,
for
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the ComicBookGalleryModel.Models
name space.
2:18
Then I'll set the series title property to
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The Amazing Spiderman Issue
number to 1 and
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published on to DateTime today.
2:32
Then we need to call the context
of the save changes method
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to persist the added
entitiy to the database.
2:42
After adding the comic book to
the database let's retrieve
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a list of the comic
books from the context.
2:50
We can do that by calling the to
list method on the contexts
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comic books DB set property var comcBooks,
2:59
= context.ComicBooks.ToList().
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This will retrieve all of the comic books
from the database, in no particular order.
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We'll see later how to filter and
order the results.
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We can use it for each loop to a enumerate
the collection of comic books and
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write each comic book series title
property value to the consul.
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Foreach var comic book in comic
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books then console.write
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line comicbook.seriestitle.
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Let's make a call to
the console's read line method so
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that the command window will stay
open until we press the enter key.
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Console, read line.
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Press F5 to build and start the app.
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Here's the text The Amazing Spider-Man
written to the console.
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I'll press the Enter key to
let the app finish executing.
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Then I'll press F5 to run the app again.
4:12
Now we're seeing the Amazing Spider-Man
being written to the console not once but
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twice.
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Why is this happening?
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Well we ran the app twice.
4:23
So we added a comic book
to the database twice.
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If we press enter and
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run our app again we'll see the text
written three times to the Consul.
4:30
This confirms that we can successfully
add a comic book to the database and
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retrieve the complete list of comic books.
4:39
Our application is persisting data,
but, how is this working?
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And where is our database?
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We'll answer these
questions the next section.
4:48
If you're following along and
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ran into any issues, be sure to
continue on to the next section.
4:52
We'll start with ensuring that you
have SQL Server LocalDB installed and
4:57
configured correctly.
5:00
See you then.
5:02
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