BTMash

class MyEventMigration extends Migration {
  // ...
}

/**
 * Class Constructor
 */
public function __construct() {
  // ...
}
 
/**
 * Add any additional data / clean up data for the current row / node that will be added/updated.
 */
public function prepareRow($current_row) {
  // ...
}

// Define a way to migrate the date field.
class MigrateDateFieldHandler extends MigrateFieldHandler {
  // Define the constructor of our Handler - it lets Migrate know what *types* of fields this handler is compatible against.
  public function __construct() {
    // ...
  }
 
  // Define our arguments on where this data will be found during the preparation.
  static function arguments($start_date = NULL, $end_date = NULL, $rrule = NULL, $separator = NULL) {
    // ...
  }
 
  // Based on the entity and return an array of field values to get processed.
  public function prepare($entity, array $field_info, array $instance, array $values) {
    // ...
  }
}

  public function __construct() {
    // Handle the various date field types
    $this->registerTypes(array('date', 'datestamp', 'datetime'));
  }

  static function arguments($start_date = NULL, $end_date = NULL, $rrule = NULL, $separator = NULL) {
    // Allow the prepare to know whether these arguments are fixed or their position in an array.  The separator will split the data.
    $arguments = array(
      'start_date' => $start_date,
      'end_date' => $end_date,
      'rrule' => $rrule,
      'separator' => $separator,
      'timezone' => variable_get('date_default_timezone', @date_default_timezone_get()),
    );
    return $arguments;
  }

  public function prepare($entity, array $field_info, array $instance, array $values) {
    // Get the list of values along with the arguments that were provided
    if (isset($values['arguments'])) {
      $arguments = $values['arguments'];
      unset($values['arguments']);
    }
    $date_type = $field_info['type'];
    $timezone = $field_info['settings']['tz_handling'];
    $timezone_db = $field_info['settings']['timezone_db'];
    $migration = Migration::currentMigration();
    $destination = $migration->getDestination();
    $language = isset($arguments['language']) ? $arguments['language'] : $destination->getLanguage();
    $separator = FALSE;
    if (!empty($arguments['separator'])) {
      $separator = TRUE;
    }
 
    $return = array();
    foreach ($values as $value) {
      if ($separator) {
        $date_values = explode($arguments['separator'], $value);
      }
      else {
        //@TODO Figure out base behavior in this scenario. For documentation, assume it is *not* an issue.
      }
      // Utilize the separator, check if the value is set at the argument and set to that value.
      $return[$language][] = array(
        'value' => (isset($arguments['start_date']) && isset($date_values[$arguments['start_date']])) ? $date_values[$arguments['start_date']] : '',
        'value2' => (isset($arguments['end_date']) && isset($date_values[$arguments['end_date']])) ? $date_values[$arguments['end_date']] : '',
        'rrule' => (isset($arguments['rrule']) && isset($date_values[$arguments['rrule']])) ? $date_values[$arguments['rrule']] : '',
        'timezone' => $timezone,
        'timezone_db' => $timezone_db,
      );
    }
    return $return;
  }

class MyEventMigration extends Migration {
  public function __construct() {
    // ...
    $source_fields = array(
      'nid' => t('The node ID of the page'),
      'front_page_image' => t('The front page image representing the gallery'),
      'right_side_images' => t('The associated images that were on the right side'),
      'linked_files' => t('The set of linked files'),
      'event_date_range' => t('The date range'),
      'event_dates' => t('The individual dates of the event'),
      'terms' => t('The terms for the node'),
    );
    // ...
    // Where the data will be found in my field
    $generic_date_arguments = MigrateDateFieldHandler::arguments(0, 1, NULL, '|');
    $this->addFieldMapping('field_content_date_range', 'event_date_range')
      ->arguments($generic_date_arguments);
 
    $this->addFieldMapping('field_content_date_time', 'event_dates')
      ->separator('##')
      ->arguments($generic_date_arguments);
    // ...
  }
 
  public function prepareRow($current_row) {
    // ...
    // Handle the date range
    $event_date_range_query = db_select(MY_MIGRATION_DATABASE_NAME .'.content_field_event_date', 'cfed')
      ->fields('cfed')
      ->condition('cfed.vid', $nid, '=');
 
    $results = $event_date_range_query->execute();
    foreach ($results as $row) {
      // This is to account for the lack of a timezone associated with the item. You will not require this
      $current_row->event_date_range = str_replace('T00', 'T09', $row->field_event_date_value .'|'. $row->field_event_date_value2 .'|');
    }
      // Handle the individual event dates.
    $event_date_query = db_select(REDCAT_MIGRATION_DATABASE_NAME .'.content_field_date_time', 'cfdt')
      ->fields('cfdt')
      ->condition('cfdt.vid', $nid, '=')
      ->orderBy('cfdt.delta', 'ASC');
 
    $results = $event_date_query->execute();
    $dates = array();
    foreach ($results as $row) {
      $dates[] = $row->field_date_time_value .'|'. $row->field_date_time_value2 .'|';
    }
 
    // Implode the date array with a double hash separator.  This is used as the separator from the constructor.
    $current_row->event_dates = implode('##', $dates);
    // ...
    return TRUE;
  }
 
}