CakePHP Questions

I've got a form that pulls info through an ajax request out of my controller. Now I'd like to validate the form fields when the ajax request is initiated. I do this by calling the validates() method in the function that executes the ajax request like so:

function doAjaxRequest() {
    $this->Order->Set($this->data);
    if($this->Order->validates()) {
        //do ajax stuff here
    }
}

Now, when the form doesn't validate, I want to display the usual error messages next to the form fields that weren't filled in right. Yet, using above code it still executes the ajax request (the view of doAjaxRequest() is called). So I probably need to abort the ajax request and return the errors to display next to the form. What would be the right way to do this? Thanks