Shows how to set up a custom calculation on a Participants Database Participant Log

pdb-custom-sum.php

<?php

/**
 * Plugin Name: PDB Custom Log Sum
 * Description: calculates a summary value for a participant log
 */

class pdb_custom_log_sum {
  
  /**
   * @var string the name of the log
   */
  private $logname = 'work_log';
  
  /**
   * sets up the filter
   */
  public function __construct()
  {
    // add the filter hander using the log's name for the filter, then link it to our method
    add_filter( 'pdblog-' . $this->logname . '_sum', array( $this, 'get_sum' ), 10, 2 );
  }
  
  /**
   * provides the sum value
   * 
   * @param int|float $sum the incoming sum value
   * @param array $log_values array of log field values
   * @return int|float the log sum
   */
  public function get_sum( $sum, $log_values )
  {
    return $this->calculate( $log_values );
  }
  
  /**
   * calculates the summary value
   * 
   * @param array $log_values
   * @return int|float summary value
   */
  private function calculate( $log_values )
  {
    // if there are no log entries, return a 0
    if ( ! is_array( $log_values ) || count( $log_values ) === 0 ) {
      return 0;
    }
    /*
     * the $log_values array is an array of data objects, 
     * one for each entry in the record's log
     * 
     * we iterate over the array and collect the values 
     * we need to calculate the sum
     */
    $total_hours = 0;
    foreach( $log_values as $entry )
    {
      // total up all the values in the "hours" field
      $total_hours += $entry->hours;
    }
    
    // get the average number of hours per day the volunteer logged
    $average = $total_hours / count($log_values);
    
    return $average;
  }
}

new pdb_custom_log_sum();