HarmonyOS 鸿蒙Next 如何将.db文件打开获得一个database对象

saveFileToCache(file:resourceManager.RawFileDescriptor, dbName:string) {
  // 创建缓存文件(当前是覆盖式创建)
  let cFile = getContext(this).getApplicationContext().databaseDir + "/entry/rdb/" + dbName
  let cacheFile = fs.openSync(cFile, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE)
// 读取缓冲区大小
let bufferSize = 30000
let buffer = new ArrayBuffer(bufferSize); //创建buffer缓冲区
// 要copy的文件的offset和length
let currentOffset = file.offset;
let lengthNeedToReed = file.length;
let readOption:ReadOptions = {
offset: currentOffset, //期望读取文件的位置。可选，默认从当前位置开始读
length: bufferSize //每次期望读取数据的长度。可选，默认缓冲区长度
}
// 后面len会一直减，直到没有
while(true) {
// 读取buffer容量的内容
let readLength = fs.readSync(file.fd, buffer, readOption);
// 写入buffer容量的内容
fs.writeSync(cacheFile.fd, buffer, {length:readLength}) //写到cacheFile里
// 判断后续内容 修改读文件的参数
// buffer没读满代表文件读完了
if (readLength < bufferSize) {
break;
}
if (readOption.offset != undefined){
readOption.offset += readLength;
}
}
console.log(“Copy Success!!!”)
fs.close(cacheFile);
}
INIT() {
// 创建数据库沙箱目录
try {
let dirPath = getContext(this).getApplicationContext().databaseDir + “/entry”
fs.mkdirSync(dirPath);
dirPath = dirPath + “/rdb”
fs.mkdirSync(dirPath);
}catch (error) {
console.error(mkdir rdbPath failed, error code: ${error.code}, message: ${error.message}.)
};
//数据库名称
let dbName:string = ‘Company.db’
//读取rawfile目录下db文件
try {
getContext(this).resourceManager.getRawFd(‘rdb/’ + dbName, (error, value) => {
if (error != null) {
console.log(callback getRawFd failed error code: ${error.code}, message: ${error.message}.);
} else {
console.info(value.length.toString())
this.saveFileToCache(value, dbName)
}
});
} catch (error) {
console.error(callback getRawFd failed, error code: ${error.code}, message: ${error.message}.)
};
} 

参考fs文件管理：https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/js-apis-file-fs-V5

场景一代码开发步骤：https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/data-persistence-by-rdb-store-0000001505752421-V5#section11675721527