通过键值型数据库实现数据持久化

场景介绍

键值型数据库存储键值对形式的数据，当需要存储的数据没有复杂的关系模型，比如存储商品名称及对应价格、员工工号及今日是否已出勤等，由于数据复杂度低，更容易兼容不同数据库版本和设备类型，因此推荐使用键值型数据库持久化此类数据。

约束限制

设备协同数据库，针对每条记录，Key的长度≤896 Byte，Value的长度<4 MB。
单版本数据库，针对每条记录，Key的长度≤1 KB，Value的长度<4 MB。
每个应用程序最多支持同时打开16个键值型分布式数据库。
键值型数据库事件回调方法中不允许进行阻塞操作，例如修改UI组件。

接口说明

以下是键值型数据库持久化功能的相关接口，大部分为异步接口。异步接口均有callback和Promise两种返回形式，下表均以callback形式为例，更多接口及使用方式请见分布式键值数据库。

接口名称	描述
createKVManager(config: KVManagerConfig): KVManager	创建一个KVManager对象实例，用于管理数据库对象。
getKVStore<T>(storeId: string, options: Options, callback: AsyncCallback<T>): void	指定Options和storeId，创建并得到指定类型的KVStore数据库。
put(key: string, value: Uint8Array\|string\|number\|boolean, callback: AsyncCallback<void>): void	添加指定类型的键值对到数据库。
get(key: string, callback: AsyncCallback<Uint8Array\|string\|boolean\|number>): void	获取指定键的值。
delete(key: string, callback: AsyncCallback<void>): void	从数据库中删除指定键值的数据。

开发步骤

若要使用键值型数据库，首先要获取一个KVManager实例，用于管理数据库对象。示例代码如下所示：

Stage模型示例：

// 导入模块
import distributedKVStore from '@ohos.data.distributedKVStore';

// Stage模型
import window from '@ohos.window';
import UIAbility from '@ohos.app.ability.UIAbility';
import { BusinessError } from '@ohos.base';

let kvManager: distributedKVStore.KVManager | undefined = undefined;

export default class EntryAbility extends UIAbility {
  onCreate() {
    let context = this.context;
    const kvManagerConfig: distributedKVStore.KVManagerConfig = {
      context: context,
      bundleName: 'com.example.datamanagertest'
    };
    try {
      // 创建KVManager实例
      kvManager = distributedKVStore.createKVManager(kvManagerConfig);
      console.info('Succeeded in creating KVManager.');
      // 继续创建获取数据库
    } catch (e) {
      let error = e as BusinessError;
      console.error(`Failed to create KVManager. Code:${error.code},message:${error.message}`);
    }
  }
}
if (kvManager !== undefined) {
   kvManager = kvManager as distributedKVStore.KVManager;
  //进行后续操作
  //...
}

FA模型示例：

// 导入模块
import distributedKVStore from '@ohos.data.distributedKVStore';

// FA模型
import featureAbility from '@ohos.ability.featureAbility';

let kvManager: distributedKVStore.KVManager | undefined = undefined;
let context = featureAbility.getContext(); // 获取context
const kvManagerConfig: distributedKVStore.KVManagerConfig = {
  context: context,
  bundleName: 'com.example.datamanagertest'
};
try {
  kvManager = distributedKVStore.createKVManager(kvManagerConfig);
  console.info('Succeeded in creating KVManager.');
  // 继续创建获取数据库
} catch (e) {
   let error = e as BusinessError;
   console.error(`Failed to create KVManager. Code:${error.code},message:${error.message}`);
}
if (kvManager !== undefined) {
  kvManager = kvManager as distributedKVStore.KVManager;
  //进行后续操作
  //...
}

创建并获取键值数据库。示例代码如下所示：

let kvStore: distributedKVStore.SingleKVStore | undefined = undefined;
try {
  const options: distributedKVStore.Options = {
    createIfMissing: true,
    encrypt: false,
    backup: false,
    autoSync: false,
    // kvStoreType不填时，默认创建多设备协同数据库
    kvStoreType: distributedKVStore.KVStoreType.SINGLE_VERSION,
    // 多设备协同数据库：kvStoreType: distributedKVStore.KVStoreType.DEVICE_COLLABORATION,
    securityLevel: distributedKVStore.SecurityLevel.S1
  };
  kvManager.getKVStore<distributedKVStore.SingleKVStore>('storeId', options, (err, store: distributedKVStore.SingleKVStore) => {
    if (err) {
      console.error(`Failed to get KVStore: Code:${err.code},message:${err.message}`);
      return;
    }
    console.info('Succeeded in getting KVStore.');
    kvStore = store;
    // 请确保获取到键值数据库实例后，再进行相关数据操作
  });
} catch (e) {
  let error = e as BusinessError;
  console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`);
}
if (kvStore !== undefined) {
  kvStore = kvStore as distributedKVStore.SingleKVStore;
    //进行后续操作
    //...
}

调用put()方法向键值数据库中插入数据。示例代码如下所示：

const KEY_TEST_STRING_ELEMENT = 'key_test_string';
const VALUE_TEST_STRING_ELEMENT = 'value_test_string';
try {
  kvStore.put(KEY_TEST_STRING_ELEMENT, VALUE_TEST_STRING_ELEMENT, (err) => {
    if (err !== undefined) {
      console.error(`Failed to put data. Code:${err.code},message:${err.message}`);
      return;
    }
    console.info('Succeeded in putting data.');
  });
} catch (e) {
  let error = e as BusinessError;
  console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`);
}

说明：

当Key值存在时，put()方法会修改其值，否则新增一条数据。

调用get()方法获取指定键的值。示例代码如下所示：

const KEY_TEST_STRING_ELEMENT = 'key_test_string';
const VALUE_TEST_STRING_ELEMENT = 'value_test_string';
try {
  kvStore.put(KEY_TEST_STRING_ELEMENT, VALUE_TEST_STRING_ELEMENT, (err) => {
    if (err !== undefined) {
      console.error(`Failed to put data. Code:${err.code},message:${err.message}`);
      return;
    }
    console.info('Succeeded in putting data.');
    kvStore = kvStore as distributedKVStore.SingleKVStore;
    kvStore.get(KEY_TEST_STRING_ELEMENT, (err, data) => {
      if (err != undefined) {
        console.error(`Failed to get data. Code:${err.code},message:${err.message}`);
        return;
      }
      console.info(`Succeeded in getting data. Data:${data}`);
    });
  });
} catch (e) {
  let error = e as BusinessError;
  console.error(`Failed to get data. Code:${error.code},message:${error.message}`);
}

调用delete()方法删除指定键值的数据。示例代码如下所示：

const KEY_TEST_STRING_ELEMENT = 'key_test_string';
const VALUE_TEST_STRING_ELEMENT = 'value_test_string';
try {
  kvStore.put(KEY_TEST_STRING_ELEMENT, VALUE_TEST_STRING_ELEMENT, (err) => {
    if (err !== undefined) {
      console.error(`Failed to put data. Code:${err.code},message:${err.message}`);
      return;
    }
    console.info('Succeeded in putting data.');
    kvStore = kvStore as distributedKVStore.SingleKVStore;
    kvStore.delete(KEY_TEST_STRING_ELEMENT, (err) => {
      if (err !== undefined) {
        console.error(`Failed to delete data. Code:${err.code},message:${err.message}`);
        return;
      }
      console.info('Succeeded in deleting data.');
    });
  });
} catch (e) {
  let error = e as BusinessError;
  console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`);
}