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Currently, all of our action method’s parameters are using the "string" data type. Let’s see how we can improve upon that design.
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Currently, all of our Add action method's
parameters are using the string data type.
0:00
This is a natural fit for values that
are being submitted by the form,
0:05
because the field values are represented
in the request body as text.
0:09
If we wanted to convert the date
parameter to an actual date time value,
0:14
we could write the following code.
0:18
First, we need a DateTime variable.
0:21
Then, we can make a call to
the DateTime.TryParse static method,
0:26
passing in the date parameter and
our DateTime variable as an out parameter.
0:32
While this approach would work,
it's a lot of extra code to write.
0:38
Fortunately, MVC's model binder
will do the work for us.
0:42
All we need to do is change
our parameter data types and
0:46
the model binder will automatically
attempt to convert the incoming values
0:50
to the expected data types.
0:55
Let's update the date parameter
to be of type DateTime,
0:57
activityId to be of type int,
duration to be of type double,
1:01
intensity to be of type
Entry.IntensityLevel,
1:08
which is an enum in the Entry class that
defines the available intensity levels,
1:17
exclude to be of type bool,
and notes can remain a string.
1:27
Go ahead and remove this bit of code,
and press F5 to run our app.
1:34
This time, let's try saving the form
without providing any values.
1:42
And we get an error.
1:48
The parameters dictionary
contains a null entry for
1:50
parameter date of non nullable
type System.DateTime.
1:53
For our method Add in our controller
EntriesController, an optional parameter
1:58
must be a reference type, a nullable type,
or be declared as an optional parameter.
2:03
That is a long-winded way of telling
us that MVC was unable to call
2:09
our action method, because the request
didn't provide a value for
2:13
the date parameter, and our action
method parameter doesn't allow nulls.
2:18
To work around this issue, we need to
update each of our parameters that
2:23
are using a data type that doesn't
allow nulls to be nullable.
2:27
So date, activityId,
duration, intensity, and
2:35
exclude all need to use
the corresponding nullable types.
2:39
That's easy to do.
2:44
We just need to add a question
mark after the data type.
2:45
DateTime?
2:51
Int?
2:56
Double?
2:59
IntensityLevel?
3:03
And bool?.
3:05
Let's run our app again and
see if that fixed the issue.
3:09
Let's start by saving our form
without providing any values.
3:14
Okay, we hit our breakpoint.
3:19
We're good so far.
3:21
Press F5 to continue.
3:23
And we're back at our form.
3:26
Let's enter values and
save the form again.
3:28
1/1/2016.
3:31
1, 23, Low, False.
3:33
And this is my note.
3:39
And save the form.
3:43
If we view the Locals window, which shows
all of the currently in scope variables,
3:45
we can see that our parameters
have all of our provided values.
3:50
Press F5 to continue.
3:54
And all of our values,
with the exception of the Exclude field,
3:57
have been redisplayed back to us.
4:01
The exclude field isn't
retaining its value
4:05
because of how MVC handles
rendering element attributes.
4:08
When MVC is writing a boolean
value to an attribute,
4:12
it will omit the attribute
if the value was false or
4:15
render the attribute name equal to
the attribute name if the value was true.
4:19
We can see this in action by supplying
a value of true and saving the form again.
4:25
Now the field value that is
redisplayed back to us is value,
4:32
which is the name of the attribute
that we're trying to set.
4:37
We can work around this issue by
converting our boolean value to a string.
4:40
First, let's surround our expression
with a set of parentheses.
4:59
Then we need to check if
the ViewBag.Exclude property is null.
5:03
And if it isn't,
call the ToString method on it.
5:07
Otherwise, we'll render an empty string.
5:13
Now, if we refresh the page,
you'll see the expected behavior.
5:18
The exclude field is now set to True.
5:28
Don't worry too much about this issue and
the workaround that we're using here.
5:31
Normally, you would use a check box to
represent a boolean value in a form,
5:35
not a text box, which prevents
this issue from even surfacing.
5:40
We'll switch to using a checkbox for
the Exclude field in the next section.
5:44
Go ahead and stop the app.
5:49
If you're using GitHub,
let's commit our changes.
5:53
Enter a commit message of Updated
the EntriesController Add
6:00
method parameter data types and
click the Commit All button.
6:07
After the break, we'll take a look
at how we can use model state
6:15
to improve our handling of invalid values.
6:18
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