Flutter使用sqflite处理数据表变更的方法详解

Future<Database> _initDB(String filePath) async {
    final dbPath = await getDatabasesPath();
    final path = join(dbPath, filePath);
    return await openDatabase(path, version: 1, onCreate: _createDB);
}

var version = await db.getVersion();

var db = await openDatabase(path,
        version: latestVersion, onCreate: _createDB, onUpgrade: _updateDB);

Future<void> _updateDB(Database db, int oldVersion, int newVersion) async {
    try {
      await db.execute('ALTER TABLE memo ADD COLUMN tags TEXT');
    } on DatabaseException catch (e) {
      if (e.isDuplicateColumnError()) {
        // 忽略该异常，该列已经存在
      } else {
        rethrow;
      }
    }
    await db.setVersion(newVersion);
  }

Future<void> _createDB(Database db, int version) async {
    await db.execute('''
      CREATE TABLE memo (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        title TEXT,
        content TEXT,
        tags TEXT,
        created_time INTEGER,
        modified_time INTEGER
      )
    ''');
  }

class Tag extends StatelessWidget {
  final String text;
  final VoidCallback onDeleted;

  const Tag({Key? key, required this.text, required this.onDeleted})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return InputChip(
      label: Text(text),
      onDeleted: onDeleted,
    );
  }
}

Column(
    crossAxisAlignment: CrossAxisAlignment.start,
    children: [
      Wrap(
        alignment: WrapAlignment.start,
        spacing: 4.0,
        runSpacing: 4.0,
        children: [
          for (final tag in _tags)
            Tag(
              text: tag,
              onDeleted: () => _removeTag(tag),
            )
        ],
      ),
      TextField(
        controller: _taGController,
        decoration: InputDecoration(
          labelText: '添加标签',
          suffixIcon: IconButton(
            icon: const Icon(Icons.add),
            onPressed: _addTag,
          ),
        ),
        onSubmitted: (_) => _addTag(),
      ),
    ],
  ),

void _addTag() {
  final newTag = _tagController.text.trim();
  if (newTag.isNotEmpty && !_tags.contains(newTag)) {
    setState(() {
      _tags.add(newTag);
      _tagController.clear();
    });
  }
}

Future<int> _saveMemo(BuildContext context) async {
  var createdTimestamp = DateTime.now().millisecondsSinceEpoch ~/ 1000;
  var modifiedTimestamp = createdTimestamp;
  var memoMap = {
    'title': _title,
    'content': _content,
    'created_time': createdTimestamp,
    'modified_time': modifiedTimestamp,
    'tags': _tags.isNotEmpty ? _tags.join('|') : '',
  };
  // 保存备忘录
  var id = await insertMemo(memoMap);
  return id;
}