public static function deletePresentationsByUserBySession($usr_id, $ses_id)
{
// Load the existing presentation for the user for this session.
$existingPresentation = Presentation::getPresentationByUserBySession($usr_id, $ses_id);
// If the user has any existing presentations during the same session time, delete them.
if ($existingPresentation != null) {
$existingPresentation->delete_presentation_for_user($usr_id);
if ($existingPresentation->pres_paired_pres_id != null) {
$pairedExistingPresentation = Presentation::getPresentation($existingPresentation->pres_paired_pres_id);
// iterate through a change of presentation ids until we get back to where we started.
// for each one, delete the associated presentations
while ($pairedExistingPresentation->pres_id != $existingPresentation->pres_id) {
$pairedExistingPresentation->delete_presentation_for_user($usr_id);
$pairedExistingPresentation = Presentation::getPresentation($pairedExistingPresentation->pres_paired_pres_id);
}
}
}
}