This trivial example checks whether an entry already exists with the current key before writing new data, in order to avoid an exception that would occur if data with this key already existed.
这个简单示例可检查在编写新数据之前当前键中是否已经有一个项，以避免因存在具有此键的数据而发生的异常。
Unlock the door with this key.
用这把钥匙开门。
Unlock the door with this key.
用这把钥匙开门。
应用推荐