Combining JQuery Validation with ASP.NET MVC

One of the most nicest things about JQuery - in addition to the powerful mechanism it provides to manipulate the HTML DOM - is the great number of very useful plugins available out there.
JQuery Validation is one of my favorites, and today we will see how this plugin can be used with the MVC framework to validate all the inputs in a form before it is submitted to the controller.
This plugin supports the concept of "validation rule", a validation that has to be performed to an input field. For instance, "The field is required", "The field should have at least N characters", or "This field has to be a valid email", many of them are the same you can find in the ASP.NET validators. (These validators do not work with the MVC framework because they are tied to the ASP.NET Viewstate). Of course, new rules can also be created for performing custom validations specific to an application, some examples of this are also available in the plugin's website.
A rule can be applied to an input field in two ways:
1. Declarative, the rule is specified in the input field by means of the class attribute:
<input name="email" id="email" maxlength="60" class="required email" type="text"/>
As you can see, two rules were specified in the class attribute, "Required" and "Email", which means that two validations have to be performed for this field. Many rules can be applied to the same field, they only have to be separated by an space.
2. Imperative in code, the rule is specified in an script:
<script type="text/javascript">
$(document).ready(function(){
  $("#form-sign-up").validate( {
    rules: {
      email: {
        required: true,
        email: true
    },
    messages: {
      email: {
        required: "Please provide an email",
        email: "Please provide a valid email"
     } });
});
</script>
The validation was attached to the input field "email" in the form "form-sign-up". The message displayed when a validation fails for an specific field can also be customized using the "messages" section in the script. (This is optional, the plugin already comes with a set of pre-defined error messages)
And finally, one of the most interesting validation rules you can find there is "remote", which performs a remote validation using an Ajax endpoint. At this point we can use an MVC controller method to perform an specific validation, for instance to see if a login name is still available to be used.
<script type="text/javascript">
$(document).ready(function(){
$("#form-sign-up").validate( {
  rules: {
    login: {
      required: true,
      remote: '<%=Url.Action("IsLoginAvailable", "Accounts") %>'
   }
  },
  messages: {
    login: {
     required: "Please provide an alias",
     remote: jQuery.format("{0} is already in use")
   }
  } });
});
</script>
The only requirement for the controller is that it must be return Json with the result of the validation. This can be easily done with MVC,

public JsonResult IsLoginAvailable(string login)

{

    //TODO: Do the validation

    JsonResult result = new JsonResult();

    if (login == "cibrax")

      result.Data = false;

    else

      result.Data = true;

    return result;

}

In the example above, if "cibrax" is entered as login name, the validation will fail and the user will see an error message.

The styles for the error messages can also be customized with the following rules,
label.error {
display: block;
color: red;
font-style: italic;
font-weight: normal;
}
input.error {
border: 2px solid red;
}
td.field input.error, td.field select.error, tr.errorRow td.field input,tr.errorRow td.field select {
border: 2px solid red;
background-color: #FFFFD5;
margin: 0px;
color: red;
}
As we have discussed here, JQuery validation is a great tool that we all should consider at the moment to validate data in the ASP.NET MVC framework.