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The Complete Guide To Validation In ASP.NET MVC 3 - Part 2
Main parts of the article follow (copy-pasted).
There are four distinct parts to creating a fully functional custom validator that works on both the client and the server. First we subclass ValidationAttribute and add our server side validation logic. Next we implement IClientValidatable on our attribute to allow HTML5 data-* attributes to be passed to the client. Thirdly, we write a custom JavaScript function that performs validation on the client. Finally, we create an adapter to transform the HTML5 attributes into a format that our custom function can understand. Whilst this sounds like a lot of work, once you get started you will find it relatively straightforward.
Subclassing ValidationAttribute
In this example, we are going to write a NotEqualTo validator that simply checks that the value of one property does not equal the value of another.
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
public sealed class NotEqualToAttribute : ValidationAttribute
{
private const string DefaultErrorMessage = "{0} cannot be the same as {1}.";
public string OtherProperty { get; private set; }
public NotEqualToAttribute(string otherProperty)
: base(DefaultErrorMessage)
{
if (string.IsNullOrEmpty(otherProperty))
{
throw new ArgumentNullException("otherProperty");
}
OtherProperty = otherProperty;
}
public override string FormatErrorMessage(string name)
{
return string.Format(ErrorMessageString, name, OtherProperty);
}
protected override ValidationResult IsValid(object value,
ValidationContext validationContext)
{
if (value != null)
{
var otherProperty = validationContext.ObjectInstance.GetType()
.GetProperty(OtherProperty);
var otherPropertyValue = otherProperty
.GetValue(validationContext.ObjectInstance, null);
if (value.Equals(otherPropertyValue))
{
return new ValidationResult(
FormatErrorMessage(validationContext.DisplayName));
}
}
return ValidationResult.Success;
}
}
Add the new attribute to the password property of the RegisterModel and run the application.
[Required]
[DataType(DataType.Password)]
[Display(Name = "Password")]
[NotEqualTo("UserName")]
public string Password { get; set; }
...
Implementing IClientValidatable
ASP.NET MVC 2 had a mechanism for adding client side validation but it was not very pretty. Thankfully in MVC 3, things have improved and the process is now fairly trivial and thankfully does not involve changing the Global.asax as in the previous version.
The first step is for your custom validation attribute to implement IClientValidatable. This is a simple, one method interface:
public IEnumerable<ModelClientValidationRule> GetClientValidationRules(
ModelMetadata metadata,
ControllerContext context)
{
var clientValidationRule = new ModelClientValidationRule()
{
ErrorMessage = FormatErrorMessage(metadata.GetDisplayName()),
ValidationType = "notequalto"
};
clientValidationRule.ValidationParameters.Add("otherproperty", OtherProperty);
return new[] { clientValidationRule };
}
If you run the application now and view source, you will see that the password input html now contains your notequalto data attributes:
<div class="editor-field">
<input data-val="true" data-val-notequalto="Password cannot be the same as UserName."
data-val-notequalto-otherproperty="UserName"
data-val-regex="Weak password detected."
data-val-regex-pattern="^(?!password$)(?!12345$).*"
data-val-required="The Password field is required."
id="Password" name="Password" type="password" />
<span class="hint">Enter your password here</span>
<span class="field-validation-valid" data-valmsg-for="Password"
data-valmsg-replace="true"></span>
</div>
Creating a custom jQuery validate function
All of this code is best to be placed in a separate JavaScript file.
(function ($) {
$.validator.addMethod("notequalto", function (value, element, params) {
if (!this.optional(element)) {
var otherProp = $('#' + params);
return (otherProp.val() !=
}
return true;
});
$.validator.unobtrusive.adapters.addSingleVal("notequalto", "otherproperty");
}(jQuery));
Depending on your validation requirements, you may find that the jquery.validate library already has the code that you need for the validation itself. There are lots of validators in jquery.validate that have not been implemented or mapped to data annotations, so if these fulfil your need, then all you need to write in javascript is an adapter or even a call to a built-in adapter which can be as little as a single line. Take a look inside jquery.validate.js to find out what is available.
Using an existing jquery.validate.unobtrusive adapter
The job of the adapter is to read the HTML5 data-* attributes on your form element and convert this data into a form that can be understood by jquery.validate and your custom validation function. You are not required to do all the work yourself though and in many cases, you can call a built-in adapter. jquery.validate.unobtrusive declares three built-in adapters which can be used in the majority of situations. These are:
jQuery.validator.unobtrusive.adapters.addBool - used when your validator does not need any additional data.
jQuery.validator.unobtrusive.adapters.addSingleVal - used when your validator takes in one piece of additional data.
jQuery.validator.unobtrusive.adapters.addMinMax - used when your validator deals with minimum and maximum values such as range or string length.
If your validator does not fit into one of these categories, you are required to write your own adapter using the jQuery.validator.unobtrusive.adapters.add method. This is not as difficulty as it sounds and we'll see an example later in the article.
We use the addSingleVal method, passing in the name of the adapter and the name of the single value that we want to pass. Should the name of the validation function differ from the adapter, you can pass in a third parameter (ruleName):
jQuery.validator.unobtrusive.adapters.addSingleVal("notequalto", "otherproperty", "mynotequaltofunction");
At this point, our custom validator is complete.
For better understanding refer to the article itself which presents more description and a more complex example.
HTH.
