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We've aligned the beginnings of the
context and controller class lifetimes,

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by instantiating an instance
of the context class,

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in the controller class constructor.

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But we still need to align
the end of the context's lifetime

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to the end of the controller's lifetime.

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We can do that, by disposing our
context when the controller's disposed.

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Let's take a moment to review,

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why it's important to dispose of
the context after you're done with it?

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As we've seen in an earlier course,
our context class inherits from

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the EF DbContext class, which
implements the IDisposable interface.

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The IDisposable interface
provides a mechanism for

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releasing unmanaged resources,
through its single method, Dispose.

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Unmanaged resources need to be released or

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cleaned up,
in order to prevent memory leaks.

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Applications that have memory
leaks will gradually, over time,

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consume more and more memory.

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Which will cause the application
to slow down, and

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potentially even slow down the server
that the application is hosted on.

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When we use our context 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 DBContext base

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class, we're letting EF know, that
the database connection can be closed.

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Previously, we placed the instantiation
of the context within a using statement.

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In order to ensure that context
isDispose method was called.

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Now that we are instantiating the context
within the controller's constructor,

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it's no longer possible
to use that approach.

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Luckily, there is a way to
explicitly dispose of the context.

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As it turns out,

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the controller base class implements the IDisposable interface.

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There are a lot of interfaces here.

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Let's scroll to the right a bit.

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And here's the IDisposable interface.

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This means,

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that the controller base class includes
a public nonvirtual Dispose method.

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The public nonvirtual Dispose method
is called by consumers of this type,

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specifically in this case,

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the MVC framework when it's
done with the controller.

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The public nonvirtual Dispose
method in turn calls this protected

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virtual Dispose method.

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The protected virtual Dispose method is
where all of the actual cleanup of managed

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and unmanaged resources is done.

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Since this method is marked
with the virtual keyword,

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we can override it in
the comicBooks controller class.

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That gives us the hook that we need in
order to explicitly dispose our context.

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Scroll down to the bottom of
the comicBooks controller class, and

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override the Dispose method.

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Remember, typing override will prompt
Visual Studio to display a list of methods

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in the base class that
are available to override.

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We can then simply just select the method
we want to override, and press enter.

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In order to guard against the case, if the
Dispose method is called more than once,

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let's define a private field to track,

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if the Dispose method
has already been called.

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Then, just inside of the Dispose method,

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let's check the value of
the disposed private field.

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And if it's true, we can short circuit
the method by immediately returning.

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The context is a managed resource.

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So we should only dispose it,
if the disposing parameter value is true.

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Following this pattern, prevents us from
attempting to release managed resources

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that may have already been reclaimed.

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Then after disposing the context, we need
to set the disposed private to true,

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indicating that the Dispose
method was called.

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Let's test our changes.

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Outside breakpoints,
just inside of the Dispose method,

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And the constructor.

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And run the web app.

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Here we are at our breakpoint,
in the constructor.

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So, our controller is being instantiated.

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Press F5 to continue execution.

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And here we are at our breakpoint
in the Dispose method.

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Now our controller is being disposed.

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Press F10 to step down to the Dispose
method call on the context.

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And F10 again, to execute the method call.

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Then F5, to continue execution again.

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And here's our list of Comic Books.

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The dispose pattern is a commonly
misunderstood design pattern that is,

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unfortunately, often
implemented incorrectly.

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For this reason, it's a good idea to
always review Microsoft's official

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documentation under MSDN website, when you
need to implement the dispose pattern.

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For more information about the dispose
pattern, see the teacher's notes.

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Now that we're properly handling
the lifetime of our context,

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let's move on to updating our controller
to handle creates and updates.