数据库备份与恢复

场景介绍

当应用在处理一项重要的操作，显然是不能被打断的。例如：写入多个表关联的事务。此时，每个表的写入都是单独的，但是表与表之间的事务关联性不能被分割。

如果操作的过程中出现问题，开发者可以使用恢复功能，将数据库恢复到之前的状态，重新对数据库进行操作。

在数据库被篡改、删除、或者设备断电场景下，数据库可能会因为数据丢失、数据损坏、脏数据等而不可用，可以通过数据库的备份恢复能力将数据库恢复至可用状态。

键值型数据库和关系型数据库均支持对数据库的备份和恢复。另外，键值型数据库还支持删除数据库备份，以释放本地存储空间。

键值型数据库备份、恢复与删除

键值型数据库，通过backup接口实现数据库备份，通过restore接口实现数据库恢复，通过deletebackup接口删除数据库备份。具体接口及功能，可见分布式键值数据库。

创建数据库。

(1) 创建kvManager。

(2) 配置数据库参数。

(3) 创建kvStore。

import distributedKVStore from '@ohos.data.distributedKVStore';
import { BusinessError } from '@ohos.base';

let kvManager: distributedKVStore.KVManager;
let kvStore: distributedKVStore.SingleKVStore | undefined = undefined;
let context = getContext(this);
const kvManagerConfig: distributedKVStore.KVManagerConfig = {
  context: context,
  bundleName: 'com.example.datamanagertest'
}
try {
  kvManager = distributedKVStore.createKVManager(kvManagerConfig);
  console.info('Succeeded in creating KVManager.');
  try {
    const options: distributedKVStore.Options = {
      createIfMissing: true,
      encrypt: true,
      backup: false,
      autoSync: true,
      kvStoreType: distributedKVStore.KVStoreType.SINGLE_VERSION,
      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;
    });
  } catch (e) {
    let error = e as BusinessError;
    console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`);
  }
} catch (e) {
  let error = e as BusinessError;
  console.error(`Failed to create KVManager. Code:${error.code},message:${error.message}`);
}

if (kvStore !== undefined) {
  kvStore = kvStore as distributedKVStore.SingleKVStore;
  //进行后续操作
  //...
}

使用put()方法插入数据。

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(`Fail 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}`);
}

使用backup()方法备份数据。

let file = 'BK001';
try {
  kvStore.backup(file, (err) => {
    if (err) {
      console.error(`Fail to backup data.code:${err.code},message:${err.message}`);
    } else {
      console.info('Succeeded in backupping data.');
    }
  });
} catch (e) {
  let error = e as BusinessError;
  console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`);
}

使用delete()方法删除数据（模拟意外删除、篡改场景）。

try {
  kvStore.delete(KEY_TEST_STRING_ELEMENT, (err) => {
    if (err !== undefined) {
      console.error(`Fail 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}`);
}

使用restore()方法恢复数据。

let file = 'BK001';
try {
  kvStore.restore(file, (err) => {
    if (err) {
      console.error(`Fail to restore data. Code:${err.code},message:${err.message}`);
    } else {
      console.info('Succeeded in restoring data.');
    }
  });
} catch (e) {
  let error = e as BusinessError;
  console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`);
}

当本地设备存储空间有限或需要重新备份时，还可使用deleteBackup()方法删除备份，释放存储空间。

let files = ['BK001'];
try {
  kvStore.deleteBackup(files).then((data) => {
    console.info(`Succeed in deleting Backup. Data:filename is ${data[0]},result is ${data[1]}.`);
  }).catch((err: BusinessError) => {
    console.error(`Fail to delete Backup. Code:${err.code},message:${err.message}`);
  })
} catch (e) {
  let error = e as BusinessError;
  console.error(`An unexpected error occurred. Code:${error.code},message:${error.message}`);
}

关系型数据库备份与恢复

关系型数据库，通过backup接口实现数据库备份，通过restore接口实现数据库恢复。具体接口及功能，可见关系型数据库。

使用getRdbStore()方法创建关系型数据库。

import relationalStore from '@ohos.data.relationalStore';
import { BusinessError } from '@ohos.base';

let store: relationalStore.RdbStore | undefined = undefined;

let context = getContext(this);

const STORE_CONFIG: relationalStore.StoreConfig = {
  name: 'RdbTest.db',
  securityLevel: relationalStore.SecurityLevel.S1
};
relationalStore.getRdbStore(context, STORE_CONFIG, (err, rdbStore) => {
  store = rdbStore;
  if (err) {
    console.error(`Failed to get RdbStore. Code:${err.code},message:${err.message}`);
    return;
  }
  store.executeSql('CREATE TABLE IF NOT EXISTS EMPLOYEE (ID INTEGER PRIMARY KEY AUTOINCREMENT, NAME TEXT NOT NULL, AGE INTEGER, SALARY REAL, CODES BLOB)', (err) => {
  })
  console.info('Succeeded in getting RdbStore.');
})

使用insert()方法插入数据。

import { ValuesBucket } from '@ohos.data.ValuesBucket';

let value1 = 'Rose';
let value2 = 18;
let value3 = 100.5;
let value4 = new Uint8Array([1, 2, 3, 4, 5]);

// 以下三种方式可用
const valueBucket1: ValuesBucket = {
  'NAME': value1,
  'AGE': value2,
  'SALARY': value3,
  'CODES': value4,
};
const valueBucket2: ValuesBucket = {
  NAME: value1,
  AGE: value2,
  SALARY: value3,
  CODES: value4,
};
const valueBucket3: ValuesBucket = {
  "NAME": value1,
  "AGE": value2,
  "SALARY": value3,
  "CODES": value4,
};

if(store != undefined) {
  (store as relationalStore.RdbStore).insert('EMPLOYEE', valueBucket1, relationalStore.ConflictResolution.ON_CONFLICT_REPLACE, (err, rowId) => {
    if (err) {
      console.error(`Failed to insert data. Code:${err.code},message:${err.message}`);
      return;
    }
    console.info(`Succeeded in inserting data. rowId:${rowId}`);
  })
}

使用backup()方法备份数据。

if(store != undefined) {
  (store as relationalStore.RdbStore).backup('dbBackup.db', (err) => {
    if (err) {
      console.error(`Failed to backup data. Code:${err.code},message:${err.message}`);
      return;
    }
    console.info('Succeeded in backuping data.');
  })
}

使用delete()方法删除数据（模拟意外删除、篡改场景）。

let predicates = new relationalStore.RdbPredicates('EMPLOYEE');
predicates.equalTo('NAME', 'Lisa');
if(store != undefined) {
  (store as relationalStore.RdbStore).delete(predicates).then((rows: number) => {
    console.info(`Delete rows: ${rows}`);
  }).catch((err: BusinessError) => {
    console.error(`Failed to delete data. Code:${err.code},message:${err.message}`);
  })
}

使用restore()方法恢复数据。

if(store != undefined) {
  (store as relationalStore.RdbStore).restore('dbBackup.db', (err) => {
    if (err) {
      console.error(`Failed to restore data. Code:${err.code},message:${err.message}`);
      return;
    }
    console.info('Succeeded in restoring data.');
  })
}