1

00:00:00,810  -->  00:00:05,550
In the last section we verified that whenever we called our action creator from our list item component

2

00:00:05,910  -->  00:00:09,400
we saw the action appear inside of our selection reducer.

3

00:00:09,450  -->  00:00:15,750
So now it's just up to us to make sure that whenever this thing sees an action of type select library

4

00:00:16,140  -->  00:00:22,420
it will return the actions payload which is libraries ID instead of all day.

5

00:00:22,440  -->  00:00:24,920
So that's all we have to do.

6

00:00:24,930  -->  00:00:30,000
I'm going to remove the two lines I have in here right now and instead I'm going to replace this with

7

00:00:30,000  -->  00:00:35,310
some boilerplate that we're going to see for just about every single producer that we ever create.

8

00:00:35,310  -->  00:00:36,040
OK.

9

00:00:36,630  -->  00:00:42,810
By convention every REDUCE-IT that we create is going to have a switch statement inside of it that is

10

00:00:42,810  -->  00:00:45,770
going to switch over the actions type.

11

00:00:46,410  -->  00:00:52,980
So the reason that we do this is to have one very nice very easy to read statement to figure out what

12

00:00:52,980  -->  00:00:57,010
this user does and more importantly what actions it responds to.

13

00:00:57,540  -->  00:01:04,700
In our case our action to reduce her wrist needs to respond to an action of Tide select library.

14

00:01:04,960  -->  00:01:14,680
So I will add in the case of select library like so I also wanted to respond to the default case.

15

00:01:14,700  -->  00:01:21,150
So if I ever get an action coming through here that is not of type select library I need to handle that

16

00:01:21,150  -->  00:01:22,280
case as well.

17

00:01:22,290  -->  00:01:28,610
So if a action comes through with type like I dunno melt motherboard or something.

18

00:01:28,610  -->  00:01:29,620
You know I don't know something.

19

00:01:29,710  -->  00:01:30,860
Something crazy like that.

20

00:01:30,990  -->  00:01:36,240
I need to make sure that I still return something from this reducer because remember all of my reducers

21

00:01:36,240  -->  00:01:41,100
can run many times throughout my applications lifecycle and I need to make sure that they always return

22

00:01:41,100  -->  00:01:43,460
some non undefined value.

23

00:01:43,670  -->  00:01:48,520
If I ever return undefined from Ray douceur redux is going to throw an error.

24

00:01:48,540  -->  00:01:54,900
So now by default if this action creator is ever seen at this reducers ever called with an action that

25

00:01:54,900  -->  00:02:01,330
it does not care about it will return whatever it returned the last time that it ran.

26

00:02:02,220  -->  00:02:09,030
So if a mysterious action comes through here with the type we don't care about just return whatever

27

00:02:09,030  -->  00:02:14,310
state we returned last time and remember the state argument right here is the state that was returned

28

00:02:14,370  -->  00:02:18,300
from the last time that the redux are from the producer Ron.

29

00:02:18,300  -->  00:02:21,880
Now how would the case in which the action is of type select library.

30

00:02:22,080  -->  00:02:29,130
Well in that case we want to return the actions payload property because inside of our action creator

31

00:02:29,190  -->  00:02:36,210
if you recall and flip over to our action Krater file we gave our action of types like the library a

32

00:02:36,210  -->  00:02:42,090
payload of the library's ID that was selected because we called the action cratered self at that library

33

00:02:42,090  -->  00:02:43,090
ID.

34

00:02:43,230  -->  00:02:49,460
So now inside my producer whenever the action is of type slides library I want to return that library's

35

00:02:49,460  -->  00:02:51,000
ID.

36

00:02:51,150  -->  00:02:57,120
The last thing you have to do in here is make sure that I handle the very default or like first initialization

37

00:02:57,120  -->  00:03:00,820
case to reduce or so the very first time the producer runs.

38

00:03:00,900  -->  00:03:06,030
And remember as we saw in the console just a second ago when redux first boots up it runs all of my

39

00:03:06,030  -->  00:03:15,860
reducers I need to make sure that I return some non undefined value from my reducer the first sign that

40

00:03:15,860  -->  00:03:19,090
runs state will be called with a value of undefined.

41

00:03:19,160  -->  00:03:24,590
So if I just let this thing run by itself I will end up returning undefined which is going to result

42

00:03:24,590  -->  00:03:25,280
in error.

43

00:03:25,400  -->  00:03:30,300
So to get around that I will always provide an initial state default argument.

44

00:03:30,310  -->  00:03:37,280
So this is going to be a little piece of ESX right here what this says right here is if this argument

45

00:03:37,280  -->  00:03:43,550
or if this argument right here is undefined we should instead default it to the value of NULL.

46

00:03:44,000  -->  00:03:49,670
So instead of returning undefined as our initial state we will return NULL which means essentially in

47

00:03:49,670  -->  00:03:52,800
our case I do not have a currently selected library.

48

00:03:52,800  -->  00:03:53,890
I just continue on.

49

00:03:53,900  -->  00:03:56,400
I don't have a selected library right now.

50

00:03:57,300  -->  00:04:00,310
OK so I know it's reducers stuff is a little bit crazy.

51

00:04:00,330  -->  00:04:01,510
Well probably a lot crazy.

52

00:04:01,520  -->  00:04:03,660
I mean I'll be really honest you it's super crazy.

53

00:04:03,980  -->  00:04:08,600
Fortunately we are going to get so much practice with reducers because they're the absolute core of

54

00:04:08,600  -->  00:04:10,300
every redux application.

55

00:04:10,310  -->  00:04:16,070
So again just like earlier when we went through our jazz playground and we were just kind of you know

56

00:04:16,210  -->  00:04:18,950
angling around with a redux a little bit.

57

00:04:18,950  -->  00:04:22,630
Even at this point in time I do not expect you to be a master of redux.

58

00:04:22,640  -->  00:04:28,490
I do not expect you to be able to rewrite all this code right here from scratch without any type of

59

00:04:28,490  -->  00:04:30,620
reference in the next app that we build.

60

00:04:30,620  -->  00:04:35,830
We will definitely go through reducers action creators actions again in great great great detail.

61

00:04:35,830  -->  00:04:38,610
So if it's still confusing do not sweat at all.

62

00:04:38,630  -->  00:04:40,970
We're going to get a lot of practice with it.

63

00:04:41,940  -->  00:04:42,510
OK.

64

00:04:42,590  -->  00:04:49,490
So at this point in time if I refreshed my simulator and then start clicking on these different things

65

00:04:49,490  -->  00:04:56,300
I don't get any feedback right now but in theory I have a piece of steak called selective library ID

66

00:04:56,720  -->  00:05:00,600
that is being changed every time I click on one of these lines right here.

67

00:05:00,770  -->  00:05:09,830
So the last thing we have to do is make sure that whenever a particular library ID is equal to the currently

68

00:05:09,830  -->  00:05:13,400
selected library ID we expand a given row.

69

00:05:13,460  -->  00:05:15,890
So let's take care of that in the next section.