如何更新版本数据库SQFLite flutter？

Question

我需要创建新表并删除本地数据库中的其他表，但是仅更改数据库版本，它不起作用，它不会创建我需要的新表。

以同样的方式我已经尝试过 onUpgrade 但它不起作用

Future<Database>  get database async{
    if( _database != null  )return _database;
    _database = await initDB();
    return _database;

  }


  initDB()async {
    Directory documentDirectory = await getApplicationDocumentsDirectory();
    String path = join( documentDirectory.path, 'DB.db' );
     var ouDb =  await openDatabase(path, version: 2,onCreate: onCreate, onUpgrade: onUpgrade);
     return ouDb;
    }

  FutureOr<void> onCreate(Database db, int version) async {

      await db.execute('CREATE TABLE nameTable0...');



      db.execute("DROP TABLE IF EXISTS NameTable1");
      db.execute("DROP TABLE IF EXISTS NameTable2");



  }

  FutureOr<void> onUpgrade(Database db, int oldVersion, int newVersion) async{
      if (oldVersion < newVersion) {
        await db.execute('CREATE TABLE NameTable3 ...');
      }
      //onCreate(db, newVersion); 
  }

Answer 1

你需要使用onUpgrade

initDb() async {
    Directory documentDirectory = await getApplicationDocumentsDirectory();
    String path = join(documentDirectory.path, 'maindb.db');
    var ourDb = await openDatabase(path, version: 2, onCreate: _onCreate, onUpgrade: _onUpgrade);
    return ourDb;
  }

  // UPGRADE DATABASE TABLES
  void _onUpgrade(Database db, int oldVersion, int newVersion) {
    if (oldVersion < newVersion) {
      // you can execute drop table and create table
      db.execute("ALTER TABLE tb_name ADD COLUMN newCol TEXT;");
    }
  }

Answer 2

我看到很多答案解释了如何执行以下签onUpgrade入openDatabase：

 if (oldVersion < newVersion) {
      await db.execute('CREATE TABLE CUSTOMER....');
 }

这在执行第一次数据库升级（即版本 1 到 2）时有效，但在执行第二次数据库升级（例如版本 2 到 3）时会失败，因为表“CUSTOMER”已经创建。所以你需要逻辑只调用一次升级。此外，您的数据库可能使用版本 10，而用户使用版本 5，因此您只需要处理 6、7、8、9 和 10 的升级。以下是我为处理这些场景而构建的逻辑：

  static Future<Database?> getDatabase() async {

    if (_dbInstance == null) {
      var databasesPath = await getDatabasesPath();
      String path = join(databasesPath, _databaseName);

      _dbInstance = await openDatabase(path, version: _databaseVersion,
          
      onUpgrade: (Database db, int oldVersion, int newVersion) async {
        //
        //Iterate from the current version to the latest version and execute SQL statements
        for (int version = oldVersion; version < newVersion; version++) {
          await _performDBUpgrade(db, version + 1);
        }
      }, 

      onCreate: (Database db, int newVersion) async {
        //
        //Start from version 1 to current version and create DB
        for (int version = 0; version < newVersion; version++) {
          await _performDBUpgrade(db, version + 1);
        }
      });
    }

    return _dbInstance;
  }

  //Call to upgrade the database. [upgradeToVersion] is the version of SQL statements that should be
  //executed.  A version of 1 is the initial creation of the database.   Anything higher would
  //be an upgrade of the database.  This function should be called once for every version upgrade.
  //For example, if current version is 1 and user is now performing an update and new version is
  //5, then this function should be called 4 times (from `onUpgrade`), where [upgradeToVersion] would be passed a 2, 3, 4 and 5.
  
  static Future<void> _performDBUpgrade(Database db, int upgradeToVersion) async {
    switch (upgradeToVersion) {
      //Upgrade to V1 (initial creation)
      case 1:
        await _dbUpdatesVersion_1(db);
        break;

      //Upgrades for V2
      case 2:
        //await _dbUpdatesVersion_2(db);
        break;
    }
  }

  ///Database updates for Version 1 (initial creation)
  static Future<void> _dbUpdatesVersion_1(Database db) async {
      await db.execute('CREATE TABLE Customer...)');
  }