WordPress plugin to generate CSV from postmeta table data (in this case - average star ratings from the Starstruck plugin

epc-csv-export.php

<?php

/**
 * CSV Exporter bootstrap file
 *
 * This file is read by WordPress to generate the plugin information in the plugin
 * admin area. This file also includes all of the dependencies used by the plugin,
 * registers the activation and deactivation functions, and defines a function
 * that starts the plugin.
 *
 * @since             1.0.0
 * @package           EPC CSV Export
 *
 * @wordpress-plugin
 * Plugin Name:       Epic CSV Export
 * Description:       exports CSVs
 * Version:           1.0.0
 * Author:            Max Kay
 * Author URI:        https://ca.linkedin.com/in/maxkay
 * License:           GPL-2.0+
 * License URI:       http://www.gnu.org/licenses/gpl-2.0.txt
 * Text Domain:       epc-csv-export
 * Domain Path:       /languages
 */
class EPCCSVExport {

  /**
   * Constructor
   */
  public function __construct() {
    if (isset($_GET['report'])) {
      $filename = 'report-' . date('Y-m-d--H-i-s') . '.csv';

      $csv = $this->generate_csv();
      header("Pragma: public");
      header("Expires: 0");
      header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
      header("Cache-Control: private", false);
      header("Content-Type: application/octet-stream");
      header("Content-Disposition: attachment; filename={$filename};");
      header("Content-Transfer-Encoding: binary");

      echo $csv;
      exit;
    }

// Add extra menu items for admins
    add_action('admin_menu', array($this, 'admin_menu'));

// Create end-points
    add_filter('query_vars', array($this, 'query_vars'));
    add_action('parse_request', array($this, 'parse_request'));
  }

  /**
   * Add extra menu items for admins
   */
  public function admin_menu() {
    // error_log( 'admin_menu');
    add_menu_page('Export Ratings', 'Export Ratings', 'manage_options', 'download_report', array($this, 'download_report'));
  }

  /**
   * Allow for custom query variables
   */
  public function query_vars($query_vars) {
    // error_log( 'query_vars' );
    $query_vars[] = 'download_report';
    return $query_vars;
  }

  /**
   * Parse the request
   */
  public function parse_request(&$wp) {
    // error_log( 'parse_request' );
    if (array_key_exists('download_report', $wp->query_vars)) {
      $this->download_report();
      exit;
    }
  }

  /**
   * Export Star Ratings
   */
  public function download_report() {
    echo '<div class="wrap">';
    echo '<div id="icon-tools" class="icon32">
</div>';
    echo '<h2>Download CSV Report</h2>';
    echo '<p><a href="?page=download_report&report=users">'. __('Export the star ratings to CSV','epc-csv-export') . '</a></p>';
  }

  /**
   * Converting data to CSV
   */
function generate_csv() {
  // error_log( 'generate_csv2: ' );
  $csv_output = '';

  if ( !is_admin() ) {
    return;
  }
  // if ( ! isset( $_GET['bbg_export'] ) ) {
  //   return;
  // }

  $header_row = array(
    0 => 'ID',
    1 => 'Post Title',
    2 => 'Average Rating',
    3 => 'Total Votes'
  );

  $fn = function($v) { return __($v,'epc-csv-export'); };
  $arr = array_map($fn, $header_row );
  $csv_output = implode(',', $arr);

  $csv_output .= "\n";

  $data_rows = array();
  global $wpdb, $bp;
  $users = $wpdb->get_results( "SELECT p.ID id, p.post_title title, rating.meta_value rating, rating2.meta_value rating2
                                FROM {$wpdb->posts} p
                                JOIN {$wpdb->postmeta} rating
                                    ON p.ID = rating.post_id AND rating.meta_key = '_starstruck_avg'
                                JOIN {$wpdb->postmeta} rating2
                                    ON p.ID = rating2.post_id AND rating2.meta_key = '_starstruck_total'
                                WHERE
                                    p.post_type = 'product'
                                ORDER BY p.post_title ASC" );
  if(count($users) > 0){
    foreach ( $users as $u ) {
        $row = array();
        $row[0] = $u->id;
        $row[1] = $u->title;
        $row[2] = $u->rating;
        $row[3] = $u->rating2;

        $result = array_values($row);
        $result = implode(", ", $result);
        $csv_output .= $result."\n";
    }
  }

  // error_log( 'csv_output: '. print_r( $csv_output, true ) );
  return $csv_output;

}

}

// Instantiate a singleton of this plugin
$csvExport = new EPCCSVExport();