AJAX and PHP

Chapter 4If we are dealing with classic server-side validation, we call the validatePHP() method, whichreturns the name of the page the browser should be redirected to (which will be allok.php if thevalidation was successful, or index.php if not). The validation results for each field are stored inthe session and if it gets reloaded, index.php will show the fields that didn't pass the test.In the case of AJAX calls, the server composes a response that specifies if the field is valid. Theresponse is a short XML document that looks like this:0txtUsernameIf the result is 0, then txtUsername isn't valid and should be marked accordingly. If the result is 1,the field's value is valid.Next, let's look into validate.class.php. The class constructor creates a connection to the databaseand the destructor closes that connection. We then have two public methods: ValidateAJAX (handlesAJAX validation) and ValidatePHP (handles typical server-side validation).AJAX validation requires two parameters, one that holds the value to be validated ($inputValue)and one that holds the form field's ID ($fieldID). A switch block loads specific validation foreach form field. This function will return 0 if validation fails or 1 if validation is successful.The PHP validation function takes no parameters, as it will always validate the entire form (afterform submit). First we initialize the $errorsExist flag to 0. Whenever validation fails for a field,this flag will be set to 1 and we will know validation has failed. Then we need to make sure thatolder session variables are unset in order to ensure that older errors are cleared.We then check each form field against a set of custom-created rules. If validation fails, we raisethe flag ($errorsExist = 1) and set the session variable that sets the CSS class for error messageto error. If, in the end, the $errorsExist flag is still set to 0, it means that the whole validationhas been successful and we return the name of the success page, thus redirecting the browser tothat page.If errors are found, we save current user input into session variables, which will be used byindex.php to fill the form (remember that by default, when loading the page, all fields are empty).This is how we save current user input:foreach ($_POST as $key => $value){$_SESSION['values'][$key] = $_POST[$key];}$_POST is an array holding the names and values of all form elements, and it can be walkedthrough with foreach. This means that for each element inside the $_POST array, we create a newelement inside the $_SESSION['values'] array.There's nothing special to mention about validate.css. The success page (allok.php) is verysimple as well—it just displays a successful submission confirmation.143