Shows how to set up an alternate record ID scheme in Participants Database

pdb_alternate_id_field.php

<?php
/*
 * Plugin Name: Participants Database Alternate ID Field
 * Version: 0.1
 * Description: allows the use of a custom field for the general ID that is used to show a record
 * Author: xnau webdesign
 */
class PDb_alternate_id_field {
  
  /**
   * @var string name of the alternate id field
   * 
   * fill this in with the name of the field you want to use to hold your alternate ID
   */
  private $alt_id_field = 'customer_id';
  
  /**
   * @var string GET variable name
   * 
   * this is the name used in the URL to identify your ID value
   */
  const get_var = 'custid';
  
  /**
   * sets up the filters
   */
  public function __construct()
  {
    // modify the single record URL to use the alternate ID
    add_filter( 'pdb-single_record_url', array( $this, 'single_record_url' ), 50, 2 );
    
    /* provide the internal record ID to the shortcode
     * this translates the alternate ID to the internal id
     */
    add_filter( 'pdb-shortcode_call_pdb_single', array( $this, 'get_record_id' ) );
  }
  
  /**
   * alter the single record URL
   * 
   * @param string $URL
   * @param int $record_id
   * @return string URL
   */
  public function single_record_url( $URL, $record_id )
  {
    return Participants_Db::add_uri_conjunction( Participants_Db::single_record_page() ) . self::get_var . '=' . urlencode( $this->get_record_alt_id( $record_id ) );
  }
  
  /**
   * provides the record ID to the shortcode
   * 
   * @param array $params the shortcode parameters
   * @return array parameter array
   */
  public function get_record_id( $params )
  {
    $alt_id = $this->get_alt_id();
    
    if ( $alt_id ) {
      $params['record_id'] = $this->_get_record_id($alt_id);
    }
    
    return $params;
  }
  
  /**
   * gets the alternate id from the URL
   * 
   * @return string
   */
  private function get_alt_id()
  {
    return filter_input( INPUT_GET, self::get_var, FILTER_SANITIZE_STRING, FILTER_NULL_ON_FAILURE );
  }
  
  /**
   * provides the alternate ID value, given the record id
   * 
   * @global wpdb $wpdb
   * @param int $record_id
   * @return string the alternate ID for the record, empty string if not found
   */
  private function get_record_alt_id( $record_id )
  {
    global $wpdb;
    
    $alt_id = $wpdb->get_var( $wpdb->prepare( 'SELECT p.' . $this->alt_id_field . ' FROM ' . Participants_Db::participants_table() . ' p WHERE p.id = %s', urldecode( $record_id ) ) );
    
    return is_null($alt_id) ? '' : $alt_id;
  }
  
  /**
   * provides the record id, given the alt ID
   * 
   * @global wpdb $wpdb
   * @param int $alt_id
   * @return int the record ID value, 0 if not found
   */
  private function _get_record_id( $alt_id )
  {
    global $wpdb;
    
    $record_id = $wpdb->get_var( $wpdb->prepare( 'SELECT p.id FROM ' . Participants_Db::participants_table() . ' p WHERE p.' . $this->alt_id_field . ' = %s', $alt_id ) );
    
    return is_null($record_id) ? 0 : $record_id;
  }
}

new PDb_alternate_id_field();

Tutorial plugin from the Using a Custom Identifier Value for Participants Database Records post on xnau.com