Demonstrates a way to check multiple fields for a match in Participants Database

pdb-check-multiple.php

<?php
/**
 * Plugin Name: PDB Multiple Field Match Check
 * Description: checks a new Participants Database submission against 
 *              the database for a matching record using multiple fields
 * Version: 1.2
 */
add_filter( 'pdb-incoming_record_match', 'xnau_check_for_match', 10, 2 );

/**
 * checks the incoming submission for a match in the database
 *
 * @global wpdb $wpdb
 * @param bool $match the current match state
 * @param array $post the new submission data
 * @return bool true if there is a match
 */
function xnau_check_for_match( $match, $post )
{
  // edit this array to set up your match fields
  $check_fields = array( 'first_name', 'last_name' );
  
  $where = array();
  $values = array();
  
  // set up the check for the same record when updating
  $exception = '';
  if (isset( $post['id'] ) ) {
    $exception = ' `id` <> %s AND ';
    $values[] = $post['id'];
  } 
  
  foreach ($check_fields as $field) {
    if ( isset( $post[$field] ) ) {
      $where[] = '`' . $field . '` LIKE "%s"';
      $values[] = trim( $post[$field] );
    }
  }
  if ( count( $where ) === 0 ) {
    //nothing to check
    return false;
  }
  $sql = 'SELECT COUNT(*) FROM ' . Participants_Db::$participants_table . ' WHERE ' . $exception . implode( ' AND ', $where );
  global $wpdb;
  $result = $wpdb->get_var( $wpdb->prepare( $sql, $values ) );

  return $result > 0;
}

If you're having trouble getting this to match your records, it's really helpful to know the exact contents of the database record you are trying to match. Open your database in phpMyAdmin (or something similar), find the plugin's main table (usually, it's wp_participants_database) and check the record your trying to match to see what the data looks like.

To see what query the function is using, you can have it dumped to your php error log with a line like this, placed just before the last return line of the function:

error_log( __FUNCTION__ . ' query: ' . $wpdb->last_query );