harmony 鸿蒙通过键值型数据库实现数据持久化
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}`);
}
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