Insert data from custom created PHP page into wp_postmeta table

Question

I am working with a Wordpress site and have created a custom page in /home/planmyme/public_html/php/ with the name response.php. On this page I am getting a value to insert in the wp_postmeta table (value examples: transaction ID, purchase ID, order ID, or item name), but I am not able to insert it.

I am using the code below as a test. I do not understand how to achieve this, or if there is any need of a database connection to run the query.

$metakey    = "_menu_item_type";
$metavalue  = "WordPress' database interface is like Sunday Morning: Easy.";

$wpdb->query( $wpdb->prepare( 
    "
        INSERT INTO $wpdb->wp_postmeta
        ( post_id, meta_key, meta_value )
        VALUES ( %d, %s, %s )
    ", 
    10, 
    $metakey, 
    $metavalue 
) );

Getting this error

Fatal error: Call to a member function query() on a non-object in /home/planmyme/public_html/php/response.php on line 56

If anybody has an idea how to do this, please let me know.

Answer 1

The error message basically says that $wpdb is not an object so you can't call any methods on it. As we can't see where $wpdb is defined in the source you posted it's hard to tell any further details.

Are you even including wordpress in your external file? You need to require wp-load.php to use the wordpress functions and classes in an external application.

Answer 2

At the moment, your PHP file doesn't recognize $wpdb object.

To utilize WordPress functions within your PHP file, you should first add WordPress support by adding below to the top of your file:

<?php require('/the/path/to/your/wp-blog-header.php'); ?>

Then you can use $wpdb - after defining it:

<?php global $wpdb; ?>

Finally, you should use either the table prefix specifically or let $wpdb do it for you. Later is preferred so a change in table prefix won't affect your PHP file. Hence your SQL should be changed to:

INSERT INTO $wpdb->postmeta

..instead of $wpdb->wp_postmeta