Validating parameters passed through the URL

I am working on an ASP.Net MVC3 application and I'm having trouble understanding the "right way" to do the validation I'm looking for.

For example, consider a model that looks like this:

    [Required]
    [StringLength(10, MinimumLength = 10)]
    [RegularExpression("[0-9]{10}")]
    public string Id { get; set; }

    [Required]
    public string Value { get;开发者_Go百科 set; }

If I have an Id of "2342" and try to POST back, the model mapping kicks in and registers an error because of the length validation. However, if perform a GET against /controller/2342, then MVC seems to happily create a model with this invalid state (ModelState.Valid will be true). I could create some validations in the controller to catch this, but it seems redundant.

What is the best way to do this?

Thanks! Jacob

When you perform a GET, you are simply retrieving a model with a given ID. So there is no validation performed. If you really want to make sure that requested model IDs should be 10 numbers in length, you should define constraint in Global.asax:

routes.MapRoute(
    "Product",
    "Product/{productId}",
    new {controller="Product", action="Details"},
    new {productId = @"[0-9]{10}" }
 );

There is nothing in the framework that by default validates a model on a GET request as validation isn't generally required at that time. If you do want to force a validation here, this was answered in this prior question See: Validate model on initial request