centos下flutter如何数据库操作 - 问答

在CentOS系统下使用Flutter进行数据库操作，通常会选择SQLite作为本地数据库。以下是在Flutter中使用SQLite进行数据库操作的基本步骤：

1. 添加依赖

首先，在pubspec.yaml文件中添加sqflite和path_provider依赖：

dependencies:
  flutter:
    sdk: flutter
  sqflite: ^2.0.0+4
  path_provider: ^2.0.2

然后运行flutter pub get命令来安装这些依赖。

2. 初始化数据库

创建一个数据库帮助类，用于初始化数据库和创建表：

import 'package:path/path.dart';
import 'package:path_provider/path_provider.dart';
import 'package:sqflite/sqflite.dart';

class DatabaseHelper {
  static final _databaseName = "my_database.db";
  static final _databaseVersion = 1;
  static final table = 'my_table';
  static final columnId = 'id';
  static final columnTitle = 'title';

  // Make this a singleton class.
  DatabaseHelper._privateConstructor();
  static final DatabaseHelper instance = DatabaseHelper._privateConstructor();

  // Only have a single app-wide reference to the database.
  static Database? _database;
  Future<Database> get database async => _database ??= await _initDatabase();

  // Open the database and create the table if it doesn't exist.
  _initDatabase() async {
    Directory documentsDirectory = await getApplicationDocumentsDirectory();
    String path = join(documentsDirectory.path, _databaseName);
    return await openDatabase(path,
        version: _databaseVersion, onCreate: _onCreate);
  }

  // SQL code to create the database table.
  Future _onCreate(Database db, int version) async {
    await db.execute('''
          CREATE TABLE $table (
            $columnId INTEGER PRIMARY KEY,
            $columnTitle TEXT NOT NULL
          )
          ''');
  }

  // Helper methods to insert, update, delete and query the database.
  // ...
}

3. 插入数据

Future<int> insert(Map<String, dynamic> row) async {
  Database db = await instance.database;
  return await db.insert(table, row);
}

4. 查询数据

Future<List<Map<String, dynamic>>> query(Map<String, dynamic> query) async {
  Database db = await instance.database;
  return await db.query(table, where: query);
}

5. 更新数据

Future<int> update(Map<String, dynamic> row, String whereClause, List<String> whereArgs) async {
  Database db = await instance.database;
  return await db.update(table, row, where: whereClause, whereArgs: whereArgs);
}

6. 删除数据

Future<int> delete(String whereClause, List<String> whereArgs) async {
  Database db = await instance.database;
  return await db.delete(table, where: whereClause, whereArgs: whereArgs);
}

7. 使用数据库帮助类

在你的Flutter应用中，你可以这样使用DatabaseHelper类：

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  DatabaseHelper dbHelper = DatabaseHelper.instance;

  // Insert data
  await dbHelper.insert({'title': 'Hello, World!'});

  // Query data
  List<Map<String, dynamic>> results = await dbHelper.query({'title': 'Hello, World!'});
  print(results);

  // Update data
  await dbHelper.update({'title': 'Hello, Flutter!'}, 'title = ?', ['Hello, World!']);

  // Delete data
  await dbHelper.delete('title = ?', ['Hello, Flutter!']);
}

以上步骤展示了如何在CentOS系统下使用Flutter进行SQLite数据库的基本操作。根据你的需求，你可以扩展DatabaseHelper类，添加更多的查询方法和功能。

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