1
00:00:00,000 --> 00:00:04,896
[MUSIC]

2
00:00:04,896 --> 00:00:06,450
Welcome back.

3
00:00:06,450 --> 00:00:10,200
Another developer on our team heard
that we had just finished development of

4
00:00:10,200 --> 00:00:12,180
a comic books data model.

5
00:00:12,180 --> 00:00:14,650
They are a huge fan of comic books.

6
00:00:14,650 --> 00:00:19,910
So they took a copy of our EF model and
built a simple console app on top of it.

7
00:00:19,910 --> 00:00:21,140
Let's take a look at what they've built.

8
00:00:22,510 --> 00:00:25,804
Here's the project for
the Comic Book Library Manager console lab.

9
00:00:29,614 --> 00:00:34,120
After starting the app, we're presented
with a list of the available comic books.

10
00:00:34,120 --> 00:00:36,160
We can type a to add a comic book.

11
00:00:38,060 --> 00:00:40,030
We're prompted to select the series.

12
00:00:41,600 --> 00:00:42,886
And an issue number.

13
00:00:42,886 --> 00:00:52,330
The description, The published on date.

14
00:00:55,420 --> 00:00:59,338
The average rating.

15
00:00:59,338 --> 00:01:01,221
The artist.

16
00:01:01,221 --> 00:01:03,130
And the artists role.

17
00:01:05,390 --> 00:01:08,260
Then we're returned to
the list of comic books

18
00:01:08,260 --> 00:01:11,080
which now includes the comic
book that we just added.

19
00:01:13,240 --> 00:01:16,510
We can type a line number to view
the detail for that comic book.

20
00:01:18,760 --> 00:01:21,910
From here,
we can type u to update the comic book.

21
00:01:23,490 --> 00:01:27,720
We're then presented with a list of
the properties that we can change.

22
00:01:27,720 --> 00:01:30,725
I'll type 2 to change
the issue number value.

23
00:01:33,451 --> 00:01:37,690
Once we've made all the changes that
we want to make, enter S to save.

24
00:01:39,820 --> 00:01:43,410
Now we're viewing the detail for
our selected comic book again.

25
00:01:43,410 --> 00:01:45,920
Notice that the issue number
has been changed to five.

26
00:01:48,620 --> 00:01:53,950
We can delete the comic book by entering
D and then Y to confirm the deletion.

27
00:01:56,450 --> 00:01:59,230
And here's the list of
the comic books again

28
00:01:59,230 --> 00:02:01,450
without the comic book
that we just deleted.

29
00:02:02,900 --> 00:02:04,560
Let's review the architecture of the app.

30
00:02:05,790 --> 00:02:09,630
When they built their app, they put all
the code that interacted with the EF

31
00:02:09,630 --> 00:02:14,350
context class into its own
class named Repository.

32
00:02:14,350 --> 00:02:18,420
Whenever they need to retrieve entities
from the database or add, update, or

33
00:02:18,420 --> 00:02:19,600
delete an entity.

34
00:02:19,600 --> 00:02:22,220
They call a method on the repository class

35
00:02:22,220 --> 00:02:24,470
instead of using
the contents class directly.

36
00:02:25,500 --> 00:02:28,720
With this design the only
part of their app that has

37
00:02:28,720 --> 00:02:33,240
any knowledge of the context
class is the repository class.

38
00:02:33,240 --> 00:02:37,810
Using this approach makes it very simple
for the rest of the app to retrieve and

39
00:02:37,810 --> 00:02:39,370
persist data.

40
00:02:39,370 --> 00:02:44,175
As we've seen in previous treehouse
courses by organizing our data access

41
00:02:44,175 --> 00:02:48,839
code in this way, we're implementing
the repository design pattern.

42
00:02:48,839 --> 00:02:52,543
All of the application code
lives in the app layer,

43
00:02:52,543 --> 00:02:58,421
the repository class along with the
context and database initializer classes.

44
00:02:58,421 --> 00:03:01,830
Livein the data access layer or DAL.

45
00:03:02,870 --> 00:03:07,560
The entity classes are shared between
the app and data access layers.

46
00:03:08,660 --> 00:03:13,020
Separating our code into layers,
gives us greater flexibility.

47
00:03:13,020 --> 00:03:14,090
For example,

48
00:03:14,090 --> 00:03:19,780
we could build additional app layer
implementations like a web or desktop app.

49
00:03:19,780 --> 00:03:21,720
Or maybe even a mobile app.

50
00:03:21,720 --> 00:03:25,520
Without having to rewrite or
change the data access layer.

51
00:03:26,650 --> 00:03:30,330
In this section we'll learn how
to perform CRUD operations,

52
00:03:30,330 --> 00:03:35,690
specifically create, update and
delete with EF context class.

53
00:03:35,690 --> 00:03:40,480
As we do that we'll be implementing the
various methods in the repository class

54
00:03:40,480 --> 00:03:43,560
in the comic book library
managers data access layer.

55
00:03:44,560 --> 00:03:46,660
I'd encourage you to follow along.

56
00:03:46,660 --> 00:03:50,620
Writing code is an important
part of the learning process.

57
00:03:50,620 --> 00:03:54,360
You'll gain a deeper understanding
of the material that will cover, and

58
00:03:54,360 --> 00:03:56,290
you'll improve your retention.

59
00:03:56,290 --> 00:03:59,539
See the teacher's notes for a link to
download the Visual Studio project.

60
00:04:00,640 --> 00:04:05,660
Let's start by seeing how we can use
the EF context to create new entities.

61
00:04:05,660 --> 00:04:06,580
See you after the break.