[Update: The code is open-sourced at http://code.google.com/p/mvcvalidation/]

The asp.net mvc codeplex preview 5 version just came out a few days ago and it includes a lot nice enhancements.  For the best introduction read Scott’s post. 

Some of my favorite changes happened in validation.  Incidentally, I was already working on a post to talk about doing client and server side validation the easy way.  The inspiration came after reading Steve Sanderson’s post and watching his screencast on how he created a model-based client-side validation – very cool.

I want a simple way to perform client and server side validation for the application I am creating for my book and my objectives are simple (yet there is no easy way to do it):

1. Have a model-based validation mechanism
2. Have the least amount of repetition (DRY)
3. Client side validation using jQuery
4. Server side validation

First, I will show you how it works then I will explain how I got there.  Here is my model class for a user

   1: public class User

   2: {

   3:     public virtual string UserName { get; set; }

   4:     public virtual string Email { get; set; }

   5:     public virtual string Password { get; set; }

   6:     public virtual Guid ProviderId { get; set; }

   7: }

To add validation to it, I simply decorate it with the appropriate validation attributes.  It ends up looking like this:

public class User
{
    [ValidateNonEmpty("Username is required")]
    public virtual string UserName { get; set; }

    [ValidateNonEmpty("Email is required")]
    [ValidateEmail("Invalid email address")]
    public virtual string Email { get; set; }

    [ValidateNonEmpty("Password is required")]
    [ValidateLength(4,50,"Password should be at least 4 characters long")]
    public virtual string Password { get; set; }

    public virtual Guid ProviderId { get; set; }
}

I then generate the client script by adding 1 line of code to my view

<%=Html.ClientSideValidation("formCreateList", ViewData.Model) %>

On the server side, I simply make a call to a validation method from my controller

[Authorize]
[AcceptVerbs("POST"), ActionName("Create")]
public ActionResult Save(User newUser)
{
    AppHelper.ValidateModel(ViewData.ModelState, newUser);
    //the rest of the action code
}

If there are any validation errors on the server, I display the errors by using the framework helper method ValidationSummary.  All I have to do is add this 1 line to the view

<%=Html.ValidationSummary() %>

JavaScript

That’s all there is to it.  Now let’s talk about how it works.  The first challenge was generating the JavaScript to validate on the client. 

I decided to use the excellent jQuery Validation plugin.  The plugin gives me 2 ways to validate my form.  The first method uses classes on the the fields to be validated, for example a required email field would look like this

<input id="email" name="email" size="25"  class="required email" />

The second method uses rules that are defined in JavaScript and look like this

<script type="text/javascript"> 
$("#signupForm").validate({
        rules: {
            email: {
                required: true,
                email: true
            }
        },
        messages: {
            email: "Please enter a valid email address"
        }
    });
</script>

Check out the plugin documenation and demos to understand how it all works.

Since I was generating the script on the server and I wanted to make only one call, I went with the second option.

The script generator simply loops through all the model properties and their attributes and generate the appropriate script.  Afterthought: Now that I think about it, I could have easily generated a script to add classes to the elements using jQuery’s addClass method…  Oh well, maybe someone else will be kind enough to do it.

Castle Validator

I used the Castle Validator Component as my validation framework.  That’s where all the validation attributes you see above come from, but you can also create your own validators.  I then created a class called JQueryValidationProvider that implements IBrowserValidationGenerator interface in the Castle.Components.Validator namespace.  I haven’t implemented the entire interface and only have a couple of validations working (I will update the source code when it is all done).  Here is a couple of methods that I implemented.

public void SetEmail(string target, string violationMessage)
{
     Rules.Add(new ValidationRule(Validate.Email, violationMessage));
}
public void SetAsRequired(string target, string violationMessage)
{
    Rules.Add(new ValidationRule(Validate.Required, violationMessage));
}

As you can see, all I am really doing is just adding the validation rule to List of ValidationRules.  ValidationRule is a straight forward class and looks like this:

internal class ValidationRule
{
    public ValidationRule(Validate validate) : this(validate, null) { }
    public ValidationRule(Validate validate, string failureMessage)
        : this(validate, failureMessage, null) { }
    public ValidationRule(Validate validate, string failureMessage, object value)
    {
        Validate = validate;
        Value = value;
        if (failureMessage != null)
        {
            ErrorMessage = failureMessage;
        }
        else
        {
            //setup default error messages
            switch (Validate)
            {
                case Validate.Required:
                    ErrorMessage = "This field is required";
                    break;
                default:
                    ErrorMessage = "Field error";
                    break;
            }
        }

    }
    public readonly object Value;
    public readonly Validate Validate;
    public readonly string ErrorMessage;
}

The helper ClientSideValidation method simply loops through the collection of rules and generate the appropriate JavaScript.  Here it is

public static string ClientSideValidation(this HtmlHelper htmlHelper,
    string formName,
    object modelToValidate)
{
    var results = new StringBuilder();
    var rules = new StringBuilder();
    var messages = new StringBuilder();
    results.AppendFormat("$(\"#{0}\").validate({1}", formName, "{");
    results.AppendLine();
    rules.AppendFormat("rules: {0}", "{");
    messages.AppendFormat("messages: {0}", "{");

    var props = TypeDescriptor.GetProperties(modelToValidate.GetType());

    var propCounter = 0;
    foreach (PropertyDescriptor prop in props)
    {
        var generator = new JQueryValidationProvider();
        foreach (var attrib in prop.Attributes.OfType<AbstractValidationAttribute>())
        {
            var v = attrib.Build();
            v.ErrorMessage = v.ErrorMessage ?? "*";
            v.Initialize(new CachedValidationRegistry(), null);
            v.ApplyBrowserValidation(null, InputElementType.Undefined,
                                     generator, null, null);
        }

        if (generator.Rules.Count > 0)
        {
            if (propCounter > 0)
            {
                rules.Append(",");
                messages.Append(",");
            }
            rules.AppendLine();
            messages.AppendLine();
            rules.AppendFormat("{0}: {1}", prop.Name.ToLower(), "{");
            messages.AppendFormat("{0}: {1}", prop.Name.ToLower(), "{");
            rules.AppendLine();
            messages.AppendLine();

            for (var i = 0; i < generator.Rules.Count; i++)
            {
                var rule = generator.Rules[i];
                rules.AppendFormat("{0}", rule.GetRuleString());
                messages.AppendFormat("{0}", rule.GetMessageString());

                if (i < generator.Rules.Count - 1)
                {
                    rules.Append(",");
                    messages.Append(",");
                }
                else
                {
                    rules.Append("}");
                    messages.Append("}");
                }
                rules.AppendLine();
                messages.AppendLine();
            }

            propCounter++;
        }
    }

    rules.Append("},");
    messages.Append("}");
    rules.AppendLine();
    messages.AppendLine();
    results.Append(rules.ToString());
    results.Append(messages.ToString());
    results.Append("});");

    return string.Format("<script type='text/javascript'><!--{1}{0}{1}--></script>", 
                            results.ToString(), Environment.NewLine);
}

Changes

Halfway through this post, I read Steve Sanderson’s new post and Stephen Walther’s new post on validation, I made some changes to the code.  I agree with their point that the controller shouldn’t be responsible for initiating the validation and it should be done at a lower layer.  I refactored the code and my controller now looks like this

[AcceptVerbs("POST")]
public ActionResult Create(User user)
{
    try
    {
        user = new User();
        UpdateModel(user, new[] { "name", "email" });
        var service = new UserService();
        service.Save(user);
    }
    catch (RuleViolationException ex)
    {
        MvcValidator.PopulateModelStateWithErrors(user, ViewData.ModelState, ex);
    }
    return View(user);
}

The validation gets initiated at the service (business logic) layer and if there is a rule violation an exception is thrown.  I then take the exception and pass it to a helper method that populates the model state. Note: I could probably rewrite this so that the ModelState population happens before the exception throwing which will eliminate the call to the population method.

My view looks like this

<%=Html.ValidationSummary() %>
<form id="formCreate" name="formCreate" 
        action='<%=Url.Action("Create")%>' method="post">
    <label for="name">Name</label>
    <input type="text" id="name" name="name" />
    <br />
    <label for="email">Email</label>
    <input type="text" id="email" name="email" />
    <br />
    <input type="submit" value="Submit" />
</form>
<%= Html.ClientSideValidation("formCreate", ViewData.Model) %>

Now if I try to submit the form, the client script validation runs and I get these errors

If you get rid of client validation and only use server validation

to submit the form, the form would look like this

Finally, here is the client JavaScript generated in the view:

<script type='text/javascript'><!--
    $("#formCreate").validate({
        rules: {
            name: {
                required: true,
                minlength: "3",
                maxlength: "25"
            },
            email: {
                email: true,
                required: true
            }
        },
        messages: {
            name: {
                required: "Username is required",
                minlength: "Username should be between 3 and 25 characters long",
                maxlength: "Username should be between 3 and 25 characters long"
            },
            email: {
                email: "Invalid email address",
                required: "Email is required"
            }
        }
    });
--></script> 

Pros & Cons

Here is what I think the pros of this design are:

1. I love using model attributes to define validation rules
2. I like that I only need 2 lines in my view
3. I like that I don’t have to do anything in the controller other than catch an exception and call a helper method

The one thing I don’t like about this design is that it feels like there is a lot of dependencies.  I might need to refactor the code and move things around.  Here is my dependency diagram

Credit

This code was possible because of other people’s work:

Stephen Walther – link

Steve Sanderson – link and link 2

Hamilton Verissimo – link

Rick Strahl – link

Scott Guthrie – link

Source Code

Click here to download the rough-quality source code.

Let me hear what you think of this design.  What’s wrong with it?  What’s right?  Should I put this up on codeplex?