Placement of add_action() for ajax callback?

Question

This is probably a palm slap question, but I'm confused.

I created what I thought was a simple WP template page. A form to update a form to a db via ajax callback. At the bottom I placed the add_action() statements for the callback function to fire when the form submits via WP-AJAX.

I quickly realised that the callback function (the functions in the add_action() statements) were not firing. The response code from the 'done' function in my jQuery was 0... which means WP-AJAX couldn't hook into the callback function.

add_action('wp_ajax_updateuserprofileAction',        'updateuserprofileAction');
add_action('wp_ajax_nopriv_updateuserprofileAction', 'updateuserprofileAction');


function updateuserprofileAction($args) {
$nonce = $_POST['send'];

if ( !wp_verify_nonce($_POST['send'],'jch-ajax-update-userprofile') ) {
  echo $nonce;
  die ( $nonce ); }

// Read the form values
$success = false;
$senderFirstName = isset( $_POST['senderFirstName'] ) ? preg_replace( "/[^\.\-\' a-zA-Z0-9]/", "", $_POST['senderFirstName'] ) : "";
$senderLastName = isset( $_POST['senderLastName'] ) ? preg_replace( "/[^\.\-\' a-zA-Z0-9]/", "", $_POST['senderLastName'] ) : "";   
$senderEmail = isset( $_POST['senderEmail'] ) ? preg_replace( "/[^\.\-\_\@a-zA-Z0-9]/", "", $_POST['senderEmail'] ) : "";

// If all values exist, send the email
if ( $senderFirstName && $senderLastName && $senderEmail) {

    global $current_user;
    get_currentuserinfo();

    update_user_meta( $current_user->ID, 'phone', $_POST['senderPhone']);

    if($success == 1)
    {       
      die('success');
    }
}
else {
    die( 'ERROR');
}
}

Out of frustration, I moved the callback function and the add_action statements to a plug-in which also uses WP-AJAX and immediately... it works.

So my question is: why? Why can't you put add_action() statements into a template page? Or to put it another way: what are the 'rules' for where you can place add_action()?

Ideally, I'd like to keep the add_action() and the callback functions in the same file as the template page. Is there a way to do this?

Answer 1

When you send an AJAX request, wp-admin/admin-ajax.php is called, not your template file. This separate request has no knowledge of all existing code in all existing templates, because they aren’t even included.

What is included: the theme’s functions.php and plugin files. This is why your callback works in a plugin.

As a rule of thumb: templates should never contain business code. No function or class declarations, no registration of callbacks. They are templates, they should just add markup to data, nothing else.