- Adding a Data Model 4:51
- Updating the Data Model 2:39
- Creating a Data Model 2 objectives
- Using Strongly Typed Views 6:46
- Using Strongly Typed Views 2 objectives
- Improving Our View Layout 7:45
- Using Razor to Render Boolean Values 1 objective
- Applying Software Design Principles 3:26
- Software Design Principles Review 5 questions
- Adding the Repository 7:55
- Adding Repository Methods 2 objectives
- Updating the Controller 7:16
- Optional URL Parameters Review 5 questions
- Using the Visual Studio Debugger 7:07
- Validating a Bug Fix with the Debugger 5:23
- Section Review 5 questions
Preview
Video Player
00:00
00:00
Updating the Controller
7:16Now that we have our comic books repository, let’s update our controller to use it.
Now that we have our
comic books repository,
0:00
we can update our controller to use it.
0:03
Let's open the comic
books controller class.
0:05
We could use the solution explore to find
the file that we're looking for, but
0:08
let's look at another option.
0:12
Pressing control comma will open
Visual Studios, navigate to dialog.
0:14
Now we can start typing the class, method,
or property name that we're looking for.
0:19
So in this case, I'll type comic.
0:24
Visual Studio will search across
the project and show the matching items.
0:28
I'll use the down arrow key to
select the fifth item in the list,
0:32
the comic books controller class, and
then press Enter to open the file.
0:36
The navigate to dialogue is
a great way to open files
0:41
without having to take your
hands off the keyboard.
0:45
Let's add a private field for
our repository.
0:48
I'll start by typing private
ComicBookRepository.
0:52
Notice that Visual Studio
is already letting us know
1:00
that something is wrong
with our type name.
1:03
The red squiggle is a dead giveaway.
1:05
If we leave the cursor right at
the end of ComicBookRepository,
1:08
we can press control period to open
the list of suggested quick actions,
1:12
instead of having to use the mouse
to click on the light bulb icon.
1:17
The first item in the list to
add the missing using directive
1:21
is what we want to do.
1:25
So we can just press Enter
to perform this action.
1:26
Then, we can continue
with adding our field.
1:30
Let's name the field _comicBookRepository.
1:33
Notice that I'm starting the field
name with an underscore and
1:39
lower case letter, which is a common
naming convention for private fields.
1:43
Then set the field value to null.
1:47
I'll collapse the solution explorer
panel to give us more room.
1:50
Now, we need an instance
of our repository.
1:54
Let's add a constructor and
instantiate a repository within it.
1:57
Remember, that constructors
are special methods
2:03
that are called when an instance of
our class is being instantiated.
2:06
We use constructors to
initialize instance members,
2:10
which is exactly what we're
doing with our repository field.
2:13
Constructors can be identified
by their lack of a return type.
2:17
And their name,
which matches the class name.
2:21
Next, let's update the detail method.
2:24
To start, add an ID parameter of type int.
2:28
Then, let's replace the inline
instantiation of the comic book model
2:32
with a call to the repository's
get comic book method.
2:36
Be sure to pass the ID
argument into the method call.
2:41
Ready to preview our changes?
2:44
Save the controller and run the website.
2:46
I don't know about you, but I'm getting
tired of seeing our home page 404.
2:51
I promise we'll fix that soon.
2:55
But for now, go ahead and browse.
2:58
The /comic_books/detail and
we got an error.
3:00
The parameters dictionary
contains a no entry for
3:06
parameter ID of non noble
type system.in32 for
3:09
method system web
NVC Action Results detail in 32.
3:14
In comic book gallery, controllers,
comic books controller.
3:21
An optional parameter must be
a reference type, a null-able type.
3:25
Or be declared as an optional parameter.
3:29
Let's break this down.
3:32
We can see here and here that this
3:33
error message refers to our comic
books controller detail action method.
3:36
Remember how we added an ID parameter
to our detail action method.
3:41
Well, this error message is telling us
3:45
that the request didn't include
a value for the ID parameter.
3:48
So in Mvc was unable to
call our action method.
3:52
Let's take another look
at how Mvc URL routing
3:57
associates URL's with
controller action methods.
4:00
In a previous video,
we discussed that MVC uses simple
4:04
pattern matching against the URL path to
determine the name of the Controller and
4:08
Action should be used in
the form of controller/action.
4:13
So, the URL path ComicBooks/Detail
would map to a controller
4:18
named ComicBooks and
an action method named Detail.
4:24
As it turns out, the actual pattern
that MVC uses is controller/action/id.
4:29
The third part of that pattern,
the ID segment is optional.
4:37
This means that MVC can successfully
match the pattern against a URL,
4:41
even if the path doesn't
include the ID segment.
4:47
Unfortunately, MVC is getting confused
about what to do with our request for
4:50
/ComicBooks/Detail.
4:55
The problem is that even though
the ID parameter should be optional,
4:58
our detail action method only accept
an integer which isn't nullable.
5:03
So, how do we resolve this issue?
5:09
It turns out that C# provides
us with an easy solution so
5:11
that we can make the necessary
changes to our detail action method.
5:15
If we update our parameter type to be
nullable by placing a question mark
5:20
after the keyword int,
then MVC can successfully pass null for
5:24
the ID parameter if an ID value isn't
provided as part of the request.
5:29
Nullable types will be covered in
more detail in future courses.
5:34
Now, we need to do a bit
of defensive coding
5:39
by checking to see if
the ID argument is null.
5:42
And if so,
we turn a not found error to the client.
5:45
We can take advantage of the base
controllers http not found method
5:50
to return an http not found result object.
5:54
Lastly, notice that visual
studio is unhappy about passing
6:00
the ideal argument to
the repositories GetComicBook method.
6:04
Argument one cannot convert
from question mark to int.
6:08
When using a nullable type,
6:14
you need to use the value property
to get at the underlying value.
6:16
You could also use an explicit cast.
6:21
Use whichever one feels the most
readable or natural to you or
6:24
whichever one your development team
has decided is their preference and
6:29
do that consistently
throughout the project.
6:33
Restart the website, so that we can
retest the /comicbooks/detail route.
6:36
Don't forget to manually browse
to the correct route, great.
6:43
I've never been so
happy to see a 404 error.
6:47
Let's change our URL, so that it
includes the optional ID parameter.
6:51
Bomber we just encountered an unhandled
exception in our detailView
6:56
Click OK to dismiss the exception dialog.
7:02
Hm, I wonder what we did wrong.
7:06
In the next video, we'll walk through
how to use the Visual Studio debugger
7:08
to troubleshoot this error.
7:12
See you then.
7:14