Script called by AJAX from Wordpress plugin isn't getting $wpdb

Question

I'm writing a Wordpress plugin and want to use ajax to submit data. When using ajax to submit a form in the admin panel, I get this error:

Fatal error: Call to a member function insert() on a non-object in /home1/crave/public_html/wp-content/plugins/MiniCMS/add_contenttype.php on line 13

Here's the script being called. Error line is annotated.

<?php
global $wpdb;

$name = $_POST["name"];
$id = '1';
$text_inputs = $_POST["text_inputs"];
$paragraph_inputs = $_POST["paragraph_inputs"];
$map_inputs = $_POST["map_inputs"];
$file_inputs = $_POST["file_inputs"];

$contentTypeTable = $wpdb->prefix . "minicms_content_type";

//This is line 13, the problem child:
$wpdb->insert( $contentTypeTable, array(
    'name' => $name,
    'id' => $id,
    'text_inputs' => $text_inputs,
    'paragraph_inputs' => $paragraph_inputs,
    'map_inputs' => $map_inputs,
    'file_inputs' => $file_inputs
));
?>

Does anyone know why I'm not getting $wpdb to work?

Answer 1

You need to use ajax in WordPress way.

From WordPress Doc:

First add some javascript that will trigger the AJAX request:

<?php
add_action( 'admin_footer', 'my_action_javascript' );

function my_action_javascript() {
?>
<script type="text/javascript" >
jQuery(document).ready(function($) {

    var data = {
        action: 'my_action',
        whatever: 1234
    };

    // since 2.8 ajaxurl is always defined in the admin header and points to admin-ajax.php
    $.post(ajaxurl, data, function(response) {
        alert('Got this from the server: ' + response);
    });
});
</script>
<?php
}

Then, set up a PHP function that will handle that request:

add_action('wp_ajax_my_action', 'my_action_callback');

function my_action_callback() {
    global $wpdb; // this is how you get access to the database

    $whatever = intval( $_POST['whatever'] );

    $whatever += 10;

        echo $whatever;

    die(); // this is required to return a proper result
}

Reference:
1. http://codex.wordpress.org/AJAX_in_Plugins
2. http://wp.tutsplus.com/articles/getting-started-with-ajax-wordpress-pagination/