public Key<?> exists(Object entityOrKey) {
    entityOrKey = ProxyHelper.unwrap(entityOrKey);
    Key<?> key = getKey(entityOrKey);
    Object id = key.getId();
    if (id == null)
      throw new MappingException("Could not get id for " + entityOrKey.getClass().getName());

    String collName = key.getKind();
    if (collName == null) collName = getCollection(key.getKindClass()).getName();

    return find(collName, key.getKindClass()).filter(Mapper.ID_KEY, key.getId()).getKey();
  }
 public <T> UpdateResults<T> update(Key<T> key, UpdateOperations<T> ops) {
   Class<T> clazz = (Class<T>) key.getKindClass();
   if (clazz == null) clazz = (Class<T>) mapr.getClassFromKind(key.getKind());
   return updateFirst(
       createQuery(clazz).disableValidation().filter(Mapper.ID_KEY, key.getId()), ops);
 }