Can I use WP comments for custom tables?

Question

I'm using WP as the framework for my site and I have a bunch of custom tables.
Now I need to allow users to write comments to various entities. Let's say one entity is image and I want users to comment my images.

How would I go about using wp_insert_comment() when I only have an image ID and not an Post ID? (The image is not related to a post).

Example:

Using jQuery, I execute this function:

public function addComment(){
    $data = array(
        'comment_post_ID' => 123,
        'comment_author' => 'Steven',
        'comment_author_email' => '[email protected]',
        'comment_author_url' => 'http://www.storelocator.com',
        'comment_content' => 'Lorem ipsum dolor sit amet...',
        'comment_author_IP' => '127.0.0.1',
        'comment_agent' => 'Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; fr; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3',
        'comment_date' => date('d-m-Y H:i:s'),
        'comment_date_gmt' => date('d-m-Y H:i:s'),
        'comment_approved' => 0,
    );

    $comment_id = wp_insert_comment($data);
    echo 'Comment ID: '.$comment_id;
}

This works. The problem is that there is no post with the ID 123. So when I go to my admin interface I get error messages like:

Notice: Trying to get property of non-object in /var/www/storelocator/wp-includes/capabilities.php on line 1178

Notice: Trying to get property of non-object in /var/www/storelocator/wp-admin/includes/class-wp-comments-list-table.php on line 488

Is there any way I can resolve this issue?

Update
I'm trying to add some meta data, but the function is not triggered in functions.php.

This is the code I'm using so far:

// Comment submit on a car
http://mysite.com/wp-content/themes/mytheme/include/jquery.php?action=addComment&entity=car&entity_id=247

// My web service
 - More or less as above. I've added two fields:

  'entity' => $_REQUEST['entity_id'],
  'entity_id' => $_REQUEST['entity']

I've also created a post, and using this post ID for comment_post_ID.


// functions.php - This is not triggered
add_action('comment_post', 'pre_handle_comment');

function pre_handle_comment($comment_id){
  add_comment_meta($comment_id, 'entity', $_POST['comment_type']);
  // Also tried
  add_comment_meta($comment_id, 'entity', 'car');
}

Answer 1

You could create a hidden dummy post and use always its post ID as comment_post_ID. Then use a comment meta field to store the related ID from your custom table.

The other, and probably better option: use custom post types, not tables if you need something that acts like a post. Register that post type with …

'supports' => array(
    'comments',
),

… and the problem will not exist anymore.

To add custom data, hook into wp_insert_comment:

add_action( 'wp_insert_comment', 'prefix_comment_meta', 10, 2 );

function prefix_comment_meta( $id, $comment )
{
    // evaluate POST request and create comment meta
}