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ASP.NET MVC Forms

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Introducing Form Validation

4:04 with James Churchill

What is form validation? What is the difference between client-side and server-side validation?

Follow Along

To follow along commiting your changes to this course, you'll need to fork the aspnet-fitness-frog repo. Then you can clone, commit, and push your changes to your fork like this: 

git clone <your-fork>
cd aspnet-fitness-frog
git checkout tags/v4.1 -b introducing-form-validation

Additional Learning

ASP.NET MVC 5 (the version that we’re using in this course) relies upon a jQuery validation plug-in to implement client-side validations. There are other ways of implementing client-side validation, including using support available in HTML5 and leveraging vanilla JavaScript. For examples of this approach, see this page on the Mozilla Developer Network (MDN) website.

For more information about the jQuery validation plug-in that ASP.NET MVC leverages, see this page.

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    [SOUND] >> Welcome back, 0:00
    we have one last major feature to add to our form, validation. 0:05
    What is form validation? 0:11
    Form validation is a set of checks, or 0:13
    rules, that are evaluated against the users provided values. 0:16
    These rules can be defined and 0:20
    evaluated on the server, on the client, or on both the client and the server. 0:23
    Each form field can have one or more validation rules for 0:29
    example, do we have a value? 0:32
    If we have a value, does it match a specific pattern? 0:35
    Like a phone, or email address pattern, or if the value is a number, 0:39
    does it fall within a specific range of acceptable values? 0:44
    For instance does it fall between zero and ten? 0:48
    We can even compare our field values against other field values. 0:53
    Does a value like a password equal another field value like a password confirmation? 0:57
    Or if the values are numbers, is one value less than or greater than another value? 1:03
    We can even validate a value against values from a database or 1:09
    API for example is the provided username or email address 1:13
    already being used by another user the possibilities are endless. 1:19
    Why do we need foreign validation? 1:24
    On the client validation provides users with timely feedback 1:25
    without having to submit the form to the server or processing. 1:31
    This allows users to more easily understand 1:35
    how to properly use our forms and correct any mistakes that they've made. 1:37
    On the server, validation is essential in order to ensure that our 1:42
    applications only accept user data that meets our quality expectations. 1:46
    Without validation, we wouldn't have a way to protect ourselves against incomplete or 1:52
    poor quality data and while it's not a substitution for 1:57
    security, validation can even help protect against malicious data. 2:01
    Let's review some of the common goals for client-side and server-side validation. 2:07
    A very common goal for client-side validation, is to ensure that required 2:12
    fields have values before the user is allowed to submit the form to the server. 2:16
    Once we've determined that we have a value for every required field. 2:22
    It's also very common to ensure that those values are actually valid. 2:26
    For instance, if we require an email address. 2:30
    Not only do we want to check if we have a value. 2:33
    But if that value conforms to what our expectation of what an email address is. 2:36
    Another common goal of client side validation 2:42
    is to provide the user with timely feedback. 2:44
    The more time that elapsed is between when the user provides a value and 2:47
    when they receive feedback about that value the more frustrated and 2:51
    potentially confused your users will be using client-side 2:55
    validation to provide your users with timely feedback is a great feature. 2:59
    Unfortunately, it's not a replacement for server-side validation. 3:04
    In web apps or applications, users might not have JavaScript enabled. 3:09
    So client-side validation might not be able to run. 3:14
    In these scenarios, server side validation is your only chance to validate the data. 3:17
    Given that, it's not optional for 3:23
    server side validation to mirror whatever client side validation you've implemented. 3:26
    Some times validation is simpler to reason about on the server. 3:32
    This is especially true if your validation rule requires values from 3:36
    a database or API. 3:40
    At this point you might be wondering if it's worth 3:41
    even implementing client side validation. 3:45
    Luckily APS.net NVC makes it easy to add validations 3:48
    that are evaluated on both the server and the client. 3:53
    In this section, we'll see how it's done. 3:56
    In the next video, we'll start with implementing server-side validation. 4:00

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