/**
  * @see ProjectPermissionOrganisationUnitInterface::delete()
  * @return bool
  * @throws ProjectPermissionOrganisationUnitDeleteException
  * @throws ProjectPermisisonOrganisationUnitDeleteVirtualFolderException
  */
 public function delete()
 {
     global $transaction;
     if ($this->permission_id and $this->project_permission) {
         $transaction_id = $transaction->begin();
         $project_id = $this->project_permission->get_project_id();
         $project_folder_id = ProjectFolder::get_folder_by_project_id($project_id);
         $permission_string = strrev(decbin($this->project_permission->get_permission()));
         if (ProjectPermission_Access::count_entries_with_project_id_and_organisation_unit_id($project_id, $this->project_permission->get_organisation_unit_id()) <= 1) {
             $folder_id = OrganisationUnitFolder::get_folder_by_organisation_unit_id($this->project_permission->get_organisation_unit_id());
             $virtual_folder = new VirtualFolder(null);
             $virtual_folder_array = $virtual_folder->list_entries_by_folder_id($folder_id);
             foreach ($virtual_folder_array as $key => $value) {
                 $virtual_folder = new ProjectVirtualFolder($value);
                 if ($virtual_folder->is_project_vfolder() == true) {
                     $virtual_folder_id = $value;
                 }
             }
             if ($virtual_folder_id) {
                 $virtual_folder = new VirtualFolder($virtual_folder_id);
                 if ($virtual_folder->unlink_folder($project_folder_id) == false) {
                     if ($transaction_id != null) {
                         $transaction->rollback($transaction_id);
                     }
                     throw new ProjectPermissionOrganisationUnitDeleteVirtualFolderException();
                 }
             }
         }
         if (parent::delete() == true) {
             if ($transaction_id != null) {
                 $transaction->commit($transaction_id);
             }
             return true;
         } else {
             if ($transaction_id != null) {
                 $transaction->rollback($transaction_id);
             }
             throw new ProjectPermissionOrganisationUnitDeleteException();
         }
     } else {
         throw new ProjectPermissionOrganisationUnitDeleteException();
     }
 }