Filter Custom Post Type in Admin

Just like in Adding a Taxonomy Filter to Admin List for a Custom Post Type? the filter parse_query could be used, but here I’m using posts_where.

The row All | Published | ... is controlled by views_edit-{$post_type} and the $views array contains each item that’s a simple anchor tag.

First, we insert a couple of links – a separator and a Meta filter:

add_filter( 'views_edit-portfolio', 'meta_views_wpse_94630', 10, 1 );

function meta_views_wpse_94630( $views ) 
{
    $views['separator'] = '           ';
    $views['metakey'] = '<a href="https://wordpress.stackexchange.com/questions/94630/edit.php?meta_data=allorany&post_type=portfolio">Meta Key</a>';
    return $views;
}

The link contains meta_data=allorany (the custom field name), which will be used to filter by meta key.

And then, filter when needed:

add_action( 'load-edit.php', 'load_custom_filter_wpse_94630' );

function load_custom_filter_wpse_94630()
{
    global $typenow;

    // Adjust the Post Type
    if( 'portfolio' != $typenow )
        return;

    add_filter( 'posts_where' , 'posts_where_wpse_94630' );
}

function posts_where_wpse_94630( $where ) 
{
    global $wpdb;       
    if ( isset( $_GET[ 'meta_data' ] ) && !empty( $_GET[ 'meta_data' ] ) ) 
    {
        $meta = esc_sql( $_GET['meta_data'] );
        $where .= " AND ID IN (SELECT post_id FROM $wpdb->postmeta WHERE meta_key='$meta' )";
    }
    return $where;
}