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。

1. 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
     //...
   }

1. 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}`);
   }

1. 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}`);
   }

1. 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}`);
   }

1. 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}`);
   }

1. 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。

1. 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.');
   })

1. 使用insert()方法插入数据。

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

   let key1 = "NAME";
   let key2 = "AGE";
   let key3 = "SALARY";
   let key4 = "CODES";
   let value1 = "Rose";
   let value2 = 22;
   let value3 = 200.5;
   let value4 = new Uint8Array([1, 2, 3, 4, 5]);
   const valueBucket: ValuesBucket = {
     key1: value1,
     key2: value2,
     key3: value3,
     key4: value4,
   };
   if(store != undefined) {
     (store as relationalStore.RdbStore).insert('EMPLOYEE', valueBucket, 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}`);
     })
   }

1. 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.`);
     })
   }

1. 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}`);
     })
   }

1. 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.`);
     })
   }

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