Should I use add_action('publish_post or add_filter('publish_post?

Question

I am trying to trigger an extra function as soon as a certain custom post type is published

function insert_table_products($post_id, $post) {
    if ($post->post_type == 'custom-products') {
        global $wpdb;
        $custom_meta = get_post_meta($post_id);
        //print_r($custom_meta);
        //print_r($post);
        $attachments = new Attachments('my_attachments');
        if ($attachments->exist()) :
            $my_index = 0;
            $use_image = new SplFileInfo($attachments->url($my_index));
            $use_main_image = $use_image->getFilename();
        endif;

        $wpdb->insert(
                'products', array(
            'product_code' => $custom_meta['product_code'][0],
            'product_name' => $post->post_title,
            'product_img_name' => $use_main_image,
            'price' => $custom_meta['product_price'][0], //$POST['acf-field-price_patch'],
            'product_inventory' => $custom_meta['product_stock'][0], //$POST['fields[field_54df75e760b5e]'],
                )
        );
    }
}
add_filter('publish_post', 'insert_table_products', 10, 2);
//add_action( 'publish_post', 'insert_table_products', 10, 2);

Neither of the hooks work. I expected the print_r to show some data

BTW, I have also a update function, triggered by

//add_filter('edit_post', 'update_table_products', 10, 2);

which also doesn't seem to work correctly.

Any ideas?

Answer 1

publish_post doesn't work for custom post types, the correct hook (action hook) is publish_{$custom_post_type}. You should use add_action() as this is an action hook.

I also tend to make use of the transition_post_status hook which is a much more universal hook as it fires everytime a post's status is changed regardless. You can use $old_status and $new_status to check the previous and new status of a post then do something.

For a new post, you can something like this: (Requires PHP 5.3+)

add_action( 'transition_post_status', function ( $new_status, $old_status, $post )
{

    if( 'publish' == $new_status && 'publish' != $old_status && $post->post_type == 'my_post_type' ) {

        //DO SOMETHING IF NEW POST IN POST TYPE IS PUBLISHED

    }
}, 10, 3 );

EDIT

For post edits/updates, using transition_post_status, you can do

add_action( 'transition_post_status', function ( $new_status, $old_status, $post )
{

    if( 'publish' == $new_status && 'publish' == $old_status && $post->post_type == 'my_post_type' ) {

        //DO SOMETHING IF A POST IN POST TYPE IS EDITED

    }
}, 10, 3 );

For further reading regarding post status transition, you can check out the codex

EDIT 2

Custom fields, built in and from the advanced custom fields plugin uses the save_post hook, which runs after post transition, so trying to add custom fields won't work on here

For custom post types, a new hook was introduced called save_post_{$post_type} to make things easier. This hook is also recommended by the ACF forum to update custom fields.