Custom validation

I'm creating an web app using jQuery Validation and jQuery UI. I'd like to know:

• Is there some way to open a modal window only when the user forget 开发者_运维问答to fill an specific field?

• Is there some way to create a custom validation which call a SELECT to check if the username is available?

Thankss!

Is there some way to open a modal window only when the user forget to fill an specific field?

$("#buttonID").click(function () {  // on click
if ($("input[type$='text']").val().length < 1) // if all input by type=text is null
$("#model").dialog("open"); // open dialog box

*Is there some way to create a custom validation, which call a SELECT to check if the username is available? *

I would probably use an Ajax call to database using php, asp or .net to check your Database for username and respond back, (with out knowing your scripting language I cant help you further)