harmony 鸿蒙通过键值型数据库实现数据持久化(ArkTS)
通过键值型数据库实现数据持久化(ArkTS)
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<boolean |string |number |Uint8Array>): 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。 |
closeKVStore(appId: string, storeId: string, callback: AsyncCallback<void>): void | 通过storeId的值关闭指定的分布式键值数据库。 |
deleteKVStore(appId: string, storeId: string, callback: AsyncCallback<void>): void | 通过storeId的值删除指定的分布式键值数据库。 |
开发步骤
- 若要使用键值型数据库,首先要使用createKVManager()方法获取一个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 '@kit.ArkData';
// Stage模型
import { window } from '@kit.ArkUI';
import { UIAbility } from '@kit.AbilityKit';
import { BusinessError } from '@kit.BasicServicesKit';
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
if (kvManager !== undefined) {
kvManager = kvManager as distributedKVStore.KVManager;
//进行后续操作
//...
}
} catch (e) {
let error = e as BusinessError;
console.error(`Failed to create KVManager. Code:${error.code},message:${error.message}`);
}
}
}
FA模型示例:
// 导入模块
import { distributedKVStore } from '@kit.ArkData';
// FA模型
import { featureAbility } from '@kit.AbilityKit';
import { BusinessError } from '@kit.BasicServicesKit';
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
//...
}
- 使用getKVStore()方法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 {
let child1 = new distributedKVStore.FieldNode('id');
child1.type = distributedKVStore.ValueType.INTEGER;
child1.nullable = false;
child1.default = '1';
let child2 = new distributedKVStore.FieldNode('name');
child2.type = distributedKVStore.ValueType.STRING;
child2.nullable = false;
child2.default = 'zhangsan';
let schema = new distributedKVStore.Schema();
schema.root.appendChild(child1);
schema.root.appendChild(child2);
schema.indexes = ['$.id', '$.name'];
// 0表示COMPATIBLE模式,1表示STRICT模式。
schema.mode = 1;
// 支持在检查Value时,跳过skip指定的字节数,且取值范围为[0,4M-2]。
schema.skip = 0;
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,
schema: schema,
// schema未定义可以不填,定义方法请参考上方schema示例。
securityLevel: distributedKVStore.SecurityLevel.S3
};
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
if (kvStore !== undefined) {
kvStore = kvStore as distributedKVStore.SingleKVStore;
//进行后续操作
//...
}
});
} catch (e) {
let error = e as BusinessError;
console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`);
}
- 使用on()方法订阅分布式数据变化,如需关闭订阅分布式数据变化,调用off(‘dataChange’)关闭。示例代码如下所示:
try {
kvStore.on('dataChange', distributedKVStore.SubscribeType.SUBSCRIBE_TYPE_ALL, (data) => {
console.info(`dataChange callback call data: ${data}`);
});
} catch (e) {
let error = e as BusinessError;
console.error(`An unexpected error occurred. code:${error.code},message:${error.message}`);
}
- 调用put()方法向键值数据库中插入数据。示例代码如下所示:
kvStore = kvStore as distributedKVStore.SingleKVStore;
const KEY_TEST_STRING_ELEMENT = 'key_test_string';
// 如果未定义Schema则Value可以传其他符合要求的值。
const VALUE_TEST_STRING_ELEMENT = '{"id":0, "name":"lisi"}';
try {
kvStore.put(KEY_TEST_STRING_ELEMENT, VALUE_TEST_STRING_ELEMENT, (err) => {
if (err !== undefined) {
console.error(`Failed to put data. Code:${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:${error.message}`);
}
说明:
当Key值存在时,put()方法会修改其值,否则新增一条数据。
- 调用get()方法获取指定键的值。示例代码如下所示:
try {
kvStore = kvStore as distributedKVStore.SingleKVStore;
kvStore.put(KEY_TEST_STRING_ELEMENT, VALUE_TEST_STRING_ELEMENT, (err) => {
if (err !== undefined) {
console.error(`Failed to put data. Code:${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:
try {
kvStore = kvStore as distributedKVStore.SingleKVStore;
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}`);
}
调用closeKVStore()方法通过storeId的值关闭指定的分布式键值数据库。示例代码如下所示:
try { // appId为应用的bundleName kvManager = kvManager as distributedKVStore.KVManager; kvStore = undefined; kvManager.closeKVStore('appId', 'storeId', (err: BusinessError)=> { if (err) { console.error(`Failed to close KVStore.code is ${err.code},message is ${err.message}`); return; } console.info('Succeeded in closing KVStore'); }); } catch (e) { let error = e as BusinessError; console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`); }
调用deleteKVStore()方法通过storeId的值删除指定的分布式键值数据库。示例代码如下所示:
try { // appId为应用的bundleName kvManager = kvManager as distributedKVStore.KVManager; kvStore = undefined; kvManager.deleteKVStore('appId', 'storeId', (err: BusinessError)=> { if (err) { console.error(`Failed to delete KVStore.code is ${err.code},message is ${err.message}`); return; } console.info('Succeeded in deleting KVStore'); }); } catch (e) { let error = e as BusinessError; console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`); }
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