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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
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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,
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retrieve a list of comic books, and
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write the comic book series titles to the console.
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To start, we need to instantiate an instance of our context class.
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Var context = new context.
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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,
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we can see that the DbContext, implements the IDisposable interface.
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Press Alt, F12 to peak the definition for the IDisposable interface.
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The i-disposable interface provides a mechanism for
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releasing unmanaged resources through its single method dispose unmanaged
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resources need to be released or cleaned up in order to prevent memory leaks.
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Applications that have memory leaks will gradually over time consume more and
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more memory which will cause the application to slow down.
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And potentially even slow down the machine that the application is hosted on.
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When we use our contacts to persist, or retrieve data from the database,
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EF will open a connection to the database, which is an unmanaged resource.
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By calling our context's dispose method, which is inherited from the DB context
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base class, we're letting EF know that the database connection can be closed.
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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.
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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.
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Context.ComicBooks.Add(new ComicBook).
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Don't forget to add the using directive, for
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the ComicBookGalleryModel.Models name space.
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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.
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Then we need to call the context of the save changes method
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to persist the added entitiy to the database.
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After adding the comic book to the database let's retrieve
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a list of the comic books from the context.
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We can do that by calling the to list method on the contexts
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comic books DB set property var comcBooks,
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= 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.
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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.
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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.
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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.
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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.
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If you're following along and
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ran into any issues, be sure to continue on to the next section.
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We'll start with ensuring that you have SQL Server LocalDB installed and
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configured correctly.
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See you then.
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