Admin Ajax is returning 0 and not Insert data

Question

I am relatively new to jQuery and AJAX in particular. I have a small issue with the return value always being 0, though I think this is actually the success message and it's not returning anything.

I have scoured the Google-verse and I have the die() function on the PHP callback and I believe the add_actions are correct.

I am working on a local host, though I doubt that affects it and this is all in the admin, not front end. I also checked that the js is enqueued and localised.

I also tested out the basic AJAX from http://codex.wordpress.org/AJAX_in_Plugins and it also returned 0, which makes me wonder if it is something other than the code outlined below.

Right now I am just trying to make it send something back to the jQuery. Any help would be appreciated.

The jQuery

<script>
                        jQuery(document).ready(function() {
                            jQuery(".bakkah_session_registrtation").click(function(e){
                                e.preventDefault();
                                jQuery("#session_modal").slideToggle(); 
                            });

                            jQuery("#session_registration_form").submit(function(e){
                                e.preventDefault();
                                jQuery("#bakkah_submit_button").attr("disabled", "disabled");
                                var url = jQuery(this).attr("action");
                                var data = jQuery(this).serialize();
                                var obj = jQuery(this);

                                jQuery.ajax({
                                    url : url,
                                    type : "POST",
                                    data : {action : "bakkah_register_session", data : data},
                                    success : function(response){
                                        jQuery(".message_register_bakkah").html(response);
                                        jQuery("#bakkah_submit_button").removeAttr("disabled");
                                        obj[0].reset(); 
                                        console.log (response);
                                    },
                                    error: function(response) {
                                        console.log(response);            
                                    }
                                });
                            });
                        });

                        jQuery("#course_select").change(function(){
                            var course = jQuery(this).val();

                            if(course == ""){
                                jQuery("#session_select").attr("disabled", "disabled");
                                jQuery("#session_select #default_session").attr("selected", "selected");
                            }else{
                                jQuery("#session_select").removeAttr("disabled");

                                jQuery("#session_select option").each(function(){
                                    jQuery(this).prop("disabled", true);
                                });

                                jQuery("#session_select option").each(function(){
                                    if(parseInt(jQuery(this).attr("var")) == parseInt(course)){
                                        jQuery(this).prop("disabled", false);
                                    }
                                });
                            }
                        });
                    </script>

The PHP:

add_action('wp_ajax_bakkah_register_session', 'bakkah_register_session');
add_action('wp_ajax_nopriv_bakkah_register_session', 'bakkah_register_session');

function bakkah_register_session(){
    global $wpdb;

    $data = array();
    parse_str($_POST['data'], $data);   

    $insert = $wpdb->insert(
            $wpdb->prefix."bakkah_course_session_registration",
            $data
    );


    wp_die();
}

Answer 1

A 0 status from admin-ajax.php indicates that no "action" is being parsed.

When you enqueue the script you are assigning a handle, this handle needs to be used when you use wp_localize_script and additionally you need to assign the url. https://codex.wordpress.org/Function_Reference/wp_localize_script

wp_register_script( 'some_handle', 'path/to/myscript.js' );

wp_localize_script( 'some_handle', 'object_name', array( 'ajax_url' => admin_url( 'admin-ajax.php' ) );

wp_enqueue_script( 'some_handle' );

Then for the JS correctly call the URL

    jQuery.ajax({
                                url : object_name.ajax_url,
                                type : "POST",
                                dataType: "json",
                                data : {
                                    data : data,
                                    action : "bakkah_register_session"
                                },
                                success : function(response){
                                    jQuery(".message_register_bakkah").html(response);
                                    jQuery("#bakkah_submit_button").removeAttr("disabled");
                                    obj[0].reset(); 
                                    console.log (response);
                                },
                                error: function(response) {
                                    console.log(response);            
                                }
                            });

Also in your PHP you need to actually return something from the function for jQuery to process and whatever you return needs to be a json_encoded array.

    $whatever['type'] = 'Success';
    $whatever['message'] = 'Some returned msg string';  

return json_encode( $whatever );

Within your jQuery script you would then refer to these values as response.type and response.message allowing you to perform checks....

    success : function(response){
       if( response.type == 'success')    {
            // do something
       }
       else    {
            // Failed, do something else
       } 
    }