1
00:00:00,590 --> 00:00:06,130
Let's update the program.CS file to use
our context class to add a comic book,

2
00:00:06,130 --> 00:00:08,180
retrieve a list of comic books, and

3
00:00:08,180 --> 00:00:11,190
write the comic book series
titles to the console.

4
00:00:11,190 --> 00:00:15,830
To start, we need to instantiate
an instance of our context class.

5
00:00:15,830 --> 00:00:19,820
Var context = new context.

6
00:00:22,500 --> 00:00:26,820
If we press F12, to look at
the definition of our context class,

7
00:00:26,820 --> 00:00:32,190
and F12 again to look at the definition
for the DbContext class,

8
00:00:32,190 --> 00:00:37,640
we can see that the DbContext,
implements the IDisposable interface.

9
00:00:37,640 --> 00:00:42,790
Press Alt, F12 to peak the definition for
the IDisposable interface.

10
00:00:42,790 --> 00:00:45,870
The i-disposable interface
provides a mechanism for

11
00:00:45,870 --> 00:00:51,470
releasing unmanaged resources through
its single method dispose unmanaged

12
00:00:51,470 --> 00:00:56,910
resources need to be released or cleaned
up in order to prevent memory leaks.

13
00:00:56,910 --> 00:01:00,924
Applications that have memory leaks will
gradually over time consume more and

14
00:01:00,924 --> 00:01:03,983
more memory which will cause
the application to slow down.

15
00:01:03,983 --> 00:01:08,390
And potentially even slow down the machine
that the application is hosted on.

16
00:01:10,200 --> 00:01:14,330
When we use our contacts to persist,
or retrieve data from the database,

17
00:01:14,330 --> 00:01:19,850
EF will open a connection to the database,
which is an unmanaged resource.

18
00:01:19,850 --> 00:01:24,478
By calling our context's dispose method,
which is inherited from the DB context

19
00:01:24,478 --> 00:01:29,050
base class, we're letting EF know that
the database connection can be closed.

20
00:01:30,180 --> 00:01:33,755
We can easily ensure that
the context is dispose method will

21
00:01:33,755 --> 00:01:38,627
be called by placing the instantiation
of the context within a using statement.

22
00:01:43,369 --> 00:01:50,460
Using open parenthesis close parenthesis
and then a set curly braces.

23
00:01:50,460 --> 00:01:54,220
Now we can use the context to add
a comic book to the database.

24
00:01:54,220 --> 00:01:58,640
To start we need to call the add method
on the context as comic books DB set

25
00:01:58,640 --> 00:01:59,690
property.

26
00:01:59,690 --> 00:02:02,918
And pass in an instance
of the comic book model.

27
00:02:02,918 --> 00:02:08,856
Context.ComicBooks.Add(new ComicBook).

28
00:02:15,194 --> 00:02:18,198
Don't forget to add the using directive,
for

29
00:02:18,198 --> 00:02:21,519
the ComicBookGalleryModel.Models
name space.

30
00:02:21,519 --> 00:02:27,075
Then I'll set the series title property to

31
00:02:27,075 --> 00:02:32,786
The Amazing Spiderman Issue
number to 1 and

32
00:02:32,786 --> 00:02:37,120
published on to DateTime today.

33
00:02:39,280 --> 00:02:42,840
Then we need to call the context
of the save changes method

34
00:02:42,840 --> 00:02:45,300
to persist the added
entitiy to the database.

35
00:02:47,410 --> 00:02:50,520
After adding the comic book to
the database let's retrieve

36
00:02:50,520 --> 00:02:53,280
a list of the comic
books from the context.

37
00:02:53,280 --> 00:02:59,664
We can do that by calling the to
list method on the contexts

38
00:02:59,664 --> 00:03:04,585
comic books DB set property var comcBooks,

39
00:03:04,585 --> 00:03:09,250
= context.ComicBooks.ToList().

40
00:03:09,250 --> 00:03:14,420
This will retrieve all of the comic books
from the database, in no particular order.

41
00:03:14,420 --> 00:03:18,410
We'll see later how to filter and
order the results.

42
00:03:18,410 --> 00:03:23,000
We can use it for each loop to a enumerate
the collection of comic books and

43
00:03:23,000 --> 00:03:26,190
write each comic book series title
property value to the consul.

44
00:03:27,360 --> 00:03:33,236
Foreach var comic book in comic

45
00:03:33,236 --> 00:03:38,434
books then console.write

46
00:03:38,434 --> 00:03:44,790
line comicbook.seriestitle.

47
00:03:44,790 --> 00:03:47,789
Let's make a call to
the console's read line method so

48
00:03:47,789 --> 00:03:51,517
that the command window will stay
open until we press the enter key.

49
00:03:51,517 --> 00:03:55,610
Console, read line.

50
00:03:55,610 --> 00:03:58,579
Press F5 to build and start the app.

51
00:04:03,708 --> 00:04:08,490
Here's the text The Amazing Spider-Man
written to the console.

52
00:04:08,490 --> 00:04:11,110
I'll press the Enter key to
let the app finish executing.

53
00:04:12,210 --> 00:04:14,710
Then I'll press F5 to run the app again.

54
00:04:15,830 --> 00:04:20,860
Now we're seeing the Amazing Spider-Man
being written to the console not once but

55
00:04:20,860 --> 00:04:22,000
twice.

56
00:04:22,000 --> 00:04:23,370
Why is this happening?

57
00:04:23,370 --> 00:04:25,560
Well we ran the app twice.

58
00:04:25,560 --> 00:04:29,170
So we added a comic book
to the database twice.

59
00:04:29,170 --> 00:04:30,309
If we press enter and

60
00:04:30,309 --> 00:04:34,880
run our app again we'll see the text
written three times to the Consul.

61
00:04:34,880 --> 00:04:39,250
This confirms that we can successfully
add a comic book to the database and

62
00:04:39,250 --> 00:04:41,290
retrieve the complete list of comic books.

63
00:04:42,310 --> 00:04:46,560
Our application is persisting data,
but, how is this working?

64
00:04:46,560 --> 00:04:48,630
And where is our database?

65
00:04:48,630 --> 00:04:50,490
We'll answer these
questions the next section.

66
00:04:51,490 --> 00:04:52,980
If you're following along and

67
00:04:52,980 --> 00:04:57,140
ran into any issues, be sure to
continue on to the next section.

68
00:04:57,140 --> 00:05:00,940
We'll start with ensuring that you
have SQL Server LocalDB installed and

69
00:05:00,940 --> 00:05:02,420
configured correctly.

70
00:05:02,420 --> 00:05:02,940
See you then.