Client Side

Using the jQuery.validate library should be pretty simple to set up.

Specify the following settings in your Web.config file:

<appSettings>
    <add key="ClientValidationEnabled" value="true"/> 
    <add key="UnobtrusiveJavaScriptEnabled" value="true"/> 
</appSettings>

When you build up your view, you would define things like this:

@Html.LabelFor(Model => Model.EditPostViewModel.Title, true)
@Html.TextBoxFor(Model => Model.EditPostViewModel.Title, 
                                new { @class = "tb1", @Style = "width:400px;" })
@Html.ValidationMessageFor(Model => Model.EditPostViewModel.Title)

NOTE: These need to be defined within a form element

Then you would need to include the following libraries:

<script src="https://stackoverflow.com/questions/14005773/@Url.Content("~/Scripts/jquery.validate.js")" type="text/javascript"></script>
<script src="https://stackoverflow.com/questions/14005773/@Url.Content("~/Scripts/jquery.validate.unobtrusive.js")" type="text/javascript"></script>

This should be able to set you up for client side validation

Resources

• http://msdn.microsoft.com/en-us/vs2010trainingcourse_aspnetmvccustomvalidation_topic5.aspx

Server Side

NOTE: This is only for additional server side validation on top of jQuery.validation library

Perhaps something like this could help:

[ValidateAjax]
public JsonResult Edit(EditPostViewModel data)
{
    //Save data
    return Json(new { Success = true } );
}

Where ValidateAjax is an attribute defined as:

public class ValidateAjaxAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if (!filterContext.HttpContext.Request.IsAjaxRequest())
            return;

        var modelState = filterContext.Controller.ViewData.ModelState;
        if (!modelState.IsValid)
        {
            var errorModel = 
                    from x in modelState.Keys
                    where modelState[x].Errors.Count > 0
                    select new
                           {
                               key = x,
                               errors = modelState[x].Errors.
                                                      Select(y => y.ErrorMessage).
                                                      ToArray()
                           };
            filterContext.Result = new JsonResult()
                                       {
                                           Data = errorModel
                                       };
            filterContext.HttpContext.Response.StatusCode = 
                                                  (int) HttpStatusCode.BadRequest;
        }
    }
}

What this does is return a JSON object specifying all of your model errors.

Example response would be

[{
    "key":"Name",
    "errors":["The Name field is required."]
},
{
    "key":"Description",
    "errors":["The Description field is required."]
}]

This would be returned to your error handling callback of the $.ajax call

You can loop through the returned data to set the error messages as needed based on the Keys returned (I think something like $('input[name="' + err.key + '"]') would find your input element