code: public function clear($objectName = null)
      {
          if ($objectName === null) {
              // Todo: Do a real delegated clear?
              $this->unitOfWork = new UnitOfWork($this);
          } else {
              //TODO
              throw new CouchDBException("DocumentManager#clear(\$objectName) not yet implemented.");
          }
      }
docs: Clears the ObjectManager. All objects that are currently managed
  by this ObjectManager become detached.
  
  @param string $objectName if given, only objects of this type will get detached
  @throws CouchDBException