- Welcome to Entity Framework Basics 2:37
- What is Entity Framework? 4:19
- Entity Framework Review 5 questions
- Workflows: Database First 6:19
- Workflows: Model First 5:50
- Adding Our First Entity Using the Code First Workflow 6:02
- Adding an Entity 2 objectives
- Adding Our Context 3:03
- Adding a Context 2 objectives
- Using the Context 5:03
- Section Review 10 questions
Preview
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Using the Context
5:03Let'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.
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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