Demonstrates how to set up a field that shows a person's age in Participants Database

pdb_set_age_value.php

<?php

/**
 * Plugin Name: Participants Database Show Participant's Age
 * Description: Sets up a field that shows a person's age
 * Version: 2.0
 */

class pdb_set_age_value {

  // put the name of your birth date field here
  var $birth_date_field = 'birthday';
  
  // put the name of your age field here
  // the age field MUST be a 'numeric' type field
  var $age_field = 'age';

  public function __construct()
  {
    /*
     * here we set up the filter that calls our age calculation function. This is 
     * called when we are only displaying the value of the field, not in a form
     */
    add_action( 'pdb-before_field_added_to_iterator', array($this, 'set_age_value_display') );
    /*
     * here we set the action handler for altering the value when the age field 
     * is shown in a form
     */
    add_action( 'pdb-form_element_build_numeric', array( $this, 'set_age_value' ) ); 
  }

  /**
   * sets the value of the age field in a display context
   *
   * @param PDb_Field_Item $field
   * @return string HTML
   * 
   */
  public function set_age_value_display( $field )
  {
    if ( $field->name() === $this->age_field ) {
      
      // get the participnat's record data
      $record = $this->record_data( $field->record_id );
      
      // if they have the birthday value set, calc the age
      if ( isset( $record[ $this->birth_date_field ] ) && ! empty( $record[ $this->birth_date_field ] ) ) {
        
        // calculate the age
        $age = $this->get_age( $record[ $this->birth_date_field ] );
        
        // set the field's value to the participant's age
        $field->set_value( $age );
      }
    }
  }
  
  /**
   * sets the age field value in a form
   * 
   * @param PDb_Form_Element $element
   */
  public function set_age_value( $element )
  {
    if ( $element->name === $this->age_field ) {
      // set the record ID property
      $element->record_id = $this->get_id('');
      
      // get the participnat's record data
      $record = $this->record_data( $element->record_id );
      
      // now set the age value
      if ( is_numeric( $record[ $this->birth_date_field ] ) ) {
        $element->value = $this->get_age( $record[ $this->birth_date_field ] );
      }
    }
  }
  
  /**
   * calculates an age in years given the birth date
   * 
   * @see http://php.net/manual/en/class.datetime.php
   * 
   * @param int $birthdate unix timestamp
   * @return string
   */
  private function get_age( $birthdate )
  {
    // our birth date
    $dob = new DateTime("@$birthdate");
    
    $today = new DateTime();
    
    // this finds the difference between the two dates
    $diff = $today->diff($dob);
    
    return $diff->y; // return the year value for the difference
  }
  
  /**
   * provides the record data
   * 
   * @param int $id the record ID
   * @return array of record values
   */
  private function record_data( $id )
  {
    return Participants_Db::get_participant( $this->get_id( $id ) );
  }
  
  /**
   * supplies the current participant ID
   * 
   * there are several possibilities (depending on the context) for the location 
   * of this information, we need to check each one
   * 
   * @param int $id the id (if known)
   * @return int the ID
   */
  private function get_id ( $id )
  {
    if ( empty( $id ) ) {
      // this is for backward compatibility
      $id = filter_input( INPUT_GET, Participants_Db::$single_query, FILTER_SANITIZE_NUMBER_INT );
    }
    if ( empty( $id ) ) {
      $id = Participants_Db::get_participant_id( filter_input( INPUT_GET, Participants_Db::$record_query, FILTER_SANITIZE_STRING ) );
    }
    if ( empty( $id ) && is_admin() ) {
      $id = filter_input( INPUT_GET, 'id', FILTER_SANITIZE_NUMBER_INT );
    }
    if ( empty( $id ) ) {
      $id = Participants_Db::$session->get( 'pdbid' );
    }
    return $id;
  }

}

new pdb_set_age_value;