Remove user id's stored in arrays that themselves are stored in user meta of another user

Question

For a collaborative website for a company, user ID of a given user is stored in another user's meta data. For e.g.: If user A is collaborating with user B, the user ID of user A is appended to an array that contains several other user ID's and then update_user_meta is run to store the array in user B's meta data. However, when user A leaves the company his account is deleted. The action deletes the user ID from the WordPress system however the ID remains in the array stored in user B's meta data. When looking at larger scale user A's ID may appear in several other user's meta data. Since, this is a continual process there are many users having ID's of non-existent users in their meta data. This is increasing size of the arrays stored in the meta data for no reason. And the non-existent ID's keep throwing errors wherever the data is used within the site. Leading to a whole lot of mess. Though conditionals are used within the code to check for user ID existence in WordPress, there is no reason to continue storing these irrelevant ID's.

So the question is: How, can I remove non-existent user ID's from meta data of active users?

Regards, John

Answer 1

The easiest way to overcome this would be to create a custom "getter" to pull the data from the user meta which will check and clean and update "on the fly" something like this:

First create a function to check if the user exists,

function does_user_exists($user_id){
    global $wpdb;
    $user = $wpdb->get_var( $wpdb->prepare( 
        "
            SELECT user_login
            FROM $wpdb->users 
            WHERE ID = %s
        ", 
        $user_id
    ) );
    if ($user == null)
        return false;
    else
        return true;
}

then create a function that gets the meta and validates it,

function get_user_collab($user_id){
    $update_flag = false;
    $collabs = get_user_meta($user_id,'collab_meta_key',true);
    //loop over ids and check if the user exists, if not then we remove it
    foreach ((array)$collabs as $key => $uid) {
        if (!does_user_exists($uid)){
            unset($collabs[$key]);
            $update_flag = true;
        }
    }
    if ($update_flag)
        update_user_meta($user_id,'collab_meta_key',$collabs);

    return $collabs;
}

and now instead of calling get_user_meta just use get_user_collab