可以参考我这篇问答：https://developer.huawei.com/consumer/cn/forum/topic/0214200571258473073?fid=0109140870620153026

拿到路径之后就可以在当前包名的公共目录下创建数据库，进行读写操作了。

我试了下，读文件可以，rdb还是不行，

可以的！

通过 ArkTS 接口获取并访问公共目录：

目录环境能力接口（ohos.file.environment）提供获取公共目录路径的能力，支持三方应用在公共文件用户目录下进行文件访问操作。

约束限制

• 使用此方式，需确认设备具有以下系统能力：SystemCapability.FileManagement.File.Environment.FolderObtain，当前仅支持2in1设备。 

if (!canIUse('SystemCapability.FileManagement.File.Environment.FolderObtain')) {
    console.error('this api is not supported on this device');
    return;
}

• 公共目录获取接口仅用于获取公共目录路径，不对公共目录访问权限进行校验。若需访问公共目录需申请对应的公共目录访问权限。三方应用需要访问公共目录时，需通过弹窗授权向用户申请授予 Download 目录权限、Documents 目录权限或 Desktop 目录权限，具体参考访问控制-向用户申请授权。

"requestPermissions" : [
"ohos.permission.READ_WRITE_DOWNLOAD_DIRECTORY",
"ohos.permission.READ_WRITE_DOCUMENTS_DIRECTORY",
]

示例

1.获取公共目录路径。

import { BusinessError } from '@kit.BasicServicesKit';
import { Environment } from '@kit.CoreFileKit';
function getUserDirExample() {
    try {
        const downloadPath = Environment.getUserDownloadDir();
        console.info(`success to getUserDownloadDir: ${downloadPath}`);
        const documentsPath = Environment.getUserDocumentDir();
        console.info(`success to getUserDocumentDir: ${documentsPath}`);
    } catch (error) {
        const err: BusinessError = error as BusinessError;
        console.error(`failed to get user dir, Error code: ${err.code}, message: ${err.message}`);
    }
}

2.以 Download 目录为例，访问 Download 目录下的文件。

import { BusinessError } from '@kit.BasicServicesKit';
import { Environment } from '@kit.CoreFileKit';
import { fileIo as fs } from '@kit.CoreFileKit';
import { common } from '@kit.AbilityKit';
// 请在组件内获取context，确保this.getUIContext().getHostContext()返回结果为UIAbilityContext
let context = this.getUIContext().getHostContext() as common.UIAbilityContext;
function readUserDownloadDirExample(context: common.UIAbilityContext) {
    // 检查是否具有 READ_WRITE_DOWNLOAD_DIRECTORY 权限，无权限则需要向用户申请授予权限。
    try {
        // 获取 Download 目录
        const downloadPath = Environment.getUserDownloadDir();
        console.info(`success to getUserDownloadDir: ${downloadPath}`);
        const dirPath = context.filesDir;
        console.info(`success to get filesDir: ${dirPath}`);
        // 查看 Download 目录下的文件并拷贝到沙箱目录中
        let fileList: string[] = fs.listFileSync(downloadPath);
        fileList.forEach((file, index) => {
            console.info(`${downloadPath} ${index}: ${file}`);
            fs.copyFileSync(`${downloadPath}/${file}`, `${dirPath}/${file}`);
        });
        // 查看沙箱目录下对应的文件
        fileList = fs.listFileSync(dirPath);
        fileList.forEach((file, index) => {
            console.info(`${dirPath} ${index}: ${file}`);
        });
    } catch (error) {
        const err: BusinessError = error as BusinessError;
        console.error(`Error code: ${err.code}, message: ${err.message}`);
    }
}

3.以 Download 目录为例，保存文件到 Download 目录。

import { BusinessError } from '@kit.BasicServicesKit';
import { Environment } from '@kit.CoreFileKit';
import { fileIo as fs } from '@kit.CoreFileKit';
function writeUserDownloadDirExample() {
// 检查是否具有 READ_WRITE_DOWNLOAD_DIRECTORY 权限，无权限则需要向用户申请授予权限。
    try {
        // 获取 Download 目录
        const downloadPath = Environment.getUserDownloadDir();
        console.info(`success to getUserDownloadDir: ${downloadPath}`);
        // 保存 temp.txt 到 Download 目录下
        const file = fs.openSync(`${downloadPath}/temp.txt`, fs.OpenMode.CREATE | fs.OpenMode.READ_WRITE);
        fs.writeSync(file.fd, 'write a message');
        fs.closeSync(file);
    } catch (error) {
        const err: BusinessError = error as BusinessError;
        console.error(`Error code: ${err.code}, message: ${err.message}`);
    }
}