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集成 SQLite 数据库

使用 `sqflite` 软件包将 SQLite 数据库集成到 Flutter 应用中，以存储结构化的关系数据。

集成 SQLite 数据库 是 CoddyKit 上的免费 Flutter Mobile Development 课时。 这是第 2 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Flutter Mobile Development 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Flutter Mobile Development 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Storing Data with SQLite

Welcome! In this lesson, we'll learn how to integrate a local database into your Flutter app using SQLite.

SQLite is a lightweight, serverless, self-contained, and transactional relational database engine. It's perfect for storing structured data directly on the user's device without needing a separate server process.

Getting `sqflite` Ready

To use SQLite in Flutter, we rely on the popular sqflite package. It provides a robust interface to SQLite databases.

First, add it (along with path_provider and path for database file management) to your pubspec.yaml file under dependencies:

  • dependencies:
  • flutter:
  • sdk: flutter
  • sqflite: ^2.3.0
  • path_provider: ^2.1.1
  • path: ^1.8.3

Run flutter pub get in your terminal after adding these.

Database Helper Class

It's a best practice to create a dedicated "helper" class to manage your database operations. This centralizes logic for opening, creating, and executing queries.

This class will typically handle:

  • Initializing and opening the database connection.
  • Creating tables when the database is first opened.
  • Providing a single instance (singleton) of the database for the entire application.
  • Abstracting direct SQL queries.

Initializing the Database

Let's start building our DatabaseHelper. The openDatabase function is key. It takes the database file path and an onCreate callback for initial setup.

Here's how to open or create your database:

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

// NOTE: getDatabasesPath() requires Flutter context.
// This main method is for demonstration.
// In a real Flutter app, _initDatabase would be called
// from a StatefulWidget or similar.

class DatabaseHelper {
  static final DatabaseHelper _instance = DatabaseHelper._internal();
  static Database? _database;

  factory DatabaseHelper() {
    return _instance;
  }

  DatabaseHelper._internal();

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

  Future<Database> _initDatabase() async {
    // Get the default databases location for the platform
    String path = await getDatabasesPath();
    String dbPath = join(path, 'item_database.db');

    return await openDatabase(
      dbPath,
      version: 1,
      onCreate: (db, version) {
        // Table creation logic will go here
        print('Database created or opened.');
      },
    );
  }
}

void main() async {
  // This main is illustrative. sqflite operations need a
  // running Flutter app context to fully function (e.g. for getDatabasesPath).
  // When run in a Flutter app, DatabaseHelper().database
  // would ensure the DB is initialized.
  print('DatabaseHelper class defined.');
}

Creating Your First Table

Inside the onCreate callback of _initDatabase, we define our database schema using standard SQL. Let's create a simple items table.

Each item will have an id (primary key), a name (text), and a quantity (integer).

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

class DatabaseHelper {
  static final DatabaseHelper _instance = DatabaseHelper._internal();
  static Database? _database;
  factory DatabaseHelper() { return _instance; }
  DatabaseHelper._internal();
  Future<Database> get database async { if (_database != null) return _database!; _database = await _initDatabase(); return _database!; }
  Future<Database> _initDatabase() async {
    String path = await getDatabasesPath();
    String dbPath = join(path, 'item_database.db');
    return await openDatabase(dbPath, version: 1,
      onCreate: (db, version) async {
        // SQL to create the items table
        await db.execute(
          '''
          CREATE TABLE items(
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            name TEXT,
            quantity INTEGER
          )
          '''
        );
        print('Table "items" created successfully.');
      },
    );
  }
}

void main() async {
  // This main is illustrative. In a Flutter app,
  // calling DatabaseHelper().database would trigger
  // _initDatabase and the onCreate callback.
  print('Database helper configured for table creation.');
}

Creating a Data Model

To work easily with database records, define a Dart class that mirrors your table's structure. This helps map data between Dart objects and database rows (which are typically represented as Map).

Here's our Item model with toMap() and fromMap() methods:

class Item {
  final int? id;
  final String name;
  final int quantity;

  Item({this.id, required this.name, required this.quantity});

  // Convert an Item into a Map. Keys must match DB column names.
  Map<String, dynamic> toMap() {
    return {
      'id': id,
      'name': name,
      'quantity': quantity,
    };
  }

  // Create an Item object from a Map (database row).
  static Item fromMap(Map<String, dynamic> map) {
    return Item(
      id: map['id'],
      name: map['name'],
      quantity: map['quantity'],
    );
  }

  @override
  String toString() {
    return 'Item(id: $id, name: $name, quantity: $quantity)';
  }
}

void main() {
  final myItem = Item(id: 1, name: 'Apple', quantity: 5);
  print('Created Item: ${myItem.toString()}');
  print('Converted to Map: ${myItem.toMap()}');

  final itemMap = {'id': 2, 'name': 'Banana', 'quantity': 3};
  final itemFromMap = Item.fromMap(itemMap);
  print('Item from Map: ${itemFromMap.toString()}');
}

Inserting Data

Now let's add a method to our DatabaseHelper to insert new items. The insert method takes the table name and a Map (from our Item.toMap()).

It returns the id of the newly inserted row.

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

// Item class (from previous scene, for self-containment)
class Item {
  final int? id; final String name; final int quantity;
  Item({this.id, required this.name, required this.quantity});
  Map<String, dynamic> toMap() { return {'id': id, 'name': name, 'quantity': quantity}; }
  static Item fromMap(Map<String, dynamic> map) { return Item(id: map['id'], name: map['name'], quantity: map['quantity']); }
  @override
  String toString() { return 'Item(id: $id, name: $name, quantity: $quantity)'; }
}

class DatabaseHelper {
  static final DatabaseHelper _instance = DatabaseHelper._internal();
  static Database? _database;
  factory DatabaseHelper() { return _instance; }
  DatabaseHelper._internal();
  Future<Database> get database async { if (_database != null) return _database!; _database = await _initDatabase(); return _database!; }
  Future<Database> _initDatabase() async {
    String path = await getDatabasesPath();
    String dbPath = join(path, 'item_database.db');
    return await openDatabase(dbPath, version: 1,
      onCreate: (db, version) async {
        await db.execute('''
          CREATE TABLE items(id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, quantity INTEGER)
          ''');
      },
    );
  }

  Future<int> insertItem(Item item) async {
    final db = await database;
    return await db.insert(
      'items',
      item.toMap(),
      conflictAlgorithm: ConflictAlgorithm.replace, // Replace if ID exists
    );
  }
}

void main() async {
  // Illustrative main. In a Flutter app, you'd call:
  // final dbHelper = DatabaseHelper();
  // final newItem = Item(name: 'Milk', quantity: 2);
  // int id = await dbHelper.insertItem(newItem);
  // print('Inserted item with id: $id');
  print('Item insertion logic defined in DatabaseHelper.');
}

Querying Data

To read data, use the query method. It returns a List>, which you then convert back into your Dart Item objects using Item.fromMap().

You can query all items or specific ones using where clauses.

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

// Item class (for self-containment)
class Item {
  final int? id; final String name; final int quantity;
  Item({this.id, required this.name, required this.quantity});
  Map<String, dynamic> toMap() { return {'id': id, 'name': name, 'quantity': quantity}; }
  static Item fromMap(Map<String, dynamic> map) { return Item(id: map['id'], name: map['name'], quantity: map['quantity']); }
  @override
  String toString() { return 'Item(id: $id, name: $name, quantity: $quantity)'; }
}

class DatabaseHelper {
  static final DatabaseHelper _instance = DatabaseHelper._internal();
  static Database? _database;
  factory DatabaseHelper() { return _instance; }
  DatabaseHelper._internal();
  Future<Database> get database async { if (_database != null) return _database!; _database = await _initDatabase(); return _database!; }
  Future<Database> _initDatabase() async {
    String path = await getDatabasesPath();
    String dbPath = join(path, 'item_database.db');
    return await openDatabase(dbPath, version: 1,
      onCreate: (db, version) async {
        await db.execute('''
          CREATE TABLE items(id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, quantity INTEGER)
          ''');
      },
    );
  }

  Future<List<Item>> getItems() async {
    final db = await database;
    // Query all the items from the table
    final List<Map<String, dynamic>> maps = await db.query('items');

    // Convert the List<Map<String, dynamic>> into a List<Item>.
    return List.generate(maps.length, (i) {
      return Item.fromMap(maps[i]);
    });
  }
}

void main() async {
  // Illustrative main. In a Flutter app, you'd call:
  // final dbHelper = DatabaseHelper();
  // await dbHelper.insertItem(Item(name: 'Bread', quantity: 1));
  // final items = await dbHelper.getItems();
  // print('Retrieved items: $items');
  print('Item query logic defined in DatabaseHelper.');
}

Updating Data

To change an existing record, use the update method. You provide the table name, the new data as a Map, and a where clause to specify which record(s) to update.

Always use whereArgs with placeholders (?) to pass values safely and prevent SQL injection.

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

// Item class (for self-containment)
class Item {
  final int? id; final String name; final int quantity;
  Item({this.id, required this.name, required this.quantity});
  Map<String, dynamic> toMap() { return {'id': id, 'name': name, 'quantity': quantity}; }
  static Item fromMap(Map<String, dynamic> map) { return Item(id: map['id'], name: map['name'], quantity: map['quantity']); }
  @override
  String toString() { return 'Item(id: $id, name: $name, quantity: $quantity)'; }
}

class DatabaseHelper {
  static final DatabaseHelper _instance = DatabaseHelper._internal();
  static Database? _database;
  factory DatabaseHelper() { return _instance; }
  DatabaseHelper._internal();
  Future<Database> get database async { if (_database != null) return _database!; _database = await _initDatabase(); return _database!; }
  Future<Database> _initDatabase() async {
    String path = await getDatabasesPath();
    String dbPath = join(path, 'item_database.db');
    return await openDatabase(dbPath, version: 1,
      onCreate: (db, version) async {
        await db.execute('''
          CREATE TABLE items(id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, quantity INTEGER)
          ''');
      },
    );
  }

  Future<int> updateItem(Item item) async {
    final db = await database;
    return await db.update(
      'items',
      item.toMap(),
      where: 'id = ?', // Specify which item to update
      whereArgs: [item.id],
    );
  }
}

void main() async {
  // Illustrative main. In a Flutter app, you'd call:
  // final dbHelper = DatabaseHelper();
  // // Assume item with id 1 exists
  // var updatedItem = Item(id: 1, name: 'Milk', quantity: 3);
  // int count = await dbHelper.updateItem(updatedItem);
  // print('Updated $count item(s).');
  print('Item update logic defined in DatabaseHelper.');
}

Deleting Data

To remove records from your database, use the delete method. Similar to update, you provide the table name and a where clause with whereArgs to specify which records to remove.

This method returns the number of rows deleted.

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

// Item class (for self-containment)
class Item {
  final int? id; final String name; final int quantity;
  Item({this.id, required this.name, required this.quantity});
  Map<String, dynamic> toMap() { return {'id': id, 'name': name, 'quantity': quantity}; }
  static Item fromMap(Map<String, dynamic> map) { return Item(id: map['id'], name: map['name'], quantity: map['quantity']); }
  @override
  String toString() { return 'Item(id: $id, name: $name, quantity: $quantity)'; }
}

class DatabaseHelper {
  static final DatabaseHelper _instance = DatabaseHelper._internal();
  static Database? _database;
  factory DatabaseHelper() { return _instance; }
  DatabaseHelper._internal();
  Future<Database> get database async { if (_database != null) return _database!; _database = await _initDatabase(); return _database!; }
  Future<Database> _initDatabase() async {
    String path = await getDatabasesPath();
    String dbPath = join(path, 'item_database.db');
    return await openDatabase(dbPath, version: 1,
      onCreate: (db, version) async {
        await db.execute('''
          CREATE TABLE items(id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, quantity INTEGER)
          ''');
      },
    );
  }

  Future<int> deleteItem(int id) async {
    final db = await database;
    return await db.delete(
      'items',
      where: 'id = ?',
      whereArgs: [id],
    );
  }
}

void main() async {
  // Illustrative main. In a Flutter app, you'd call:
  // final dbHelper = DatabaseHelper();
  // // Assume item with id 1 exists
  // int count = await dbHelper.deleteItem(1);
  // print('Deleted $count item(s).');
  print('Item deletion logic defined in DatabaseHelper.');
}

SQLite Operations Quiz

Consider an items table with columns id (INTEGER), name (TEXT), and quantity (INTEGER).

Which sqflite method would you use to retrieve all items where the quantity is greater than 10?

Recap: SQLite & `sqflite`

Great job! You've learned the fundamentals of integrating SQLite into your Flutter app using the sqflite package.

Key takeaways:

  • SQLite is a lightweight, local, relational database.
  • The sqflite package provides Dart APIs for SQLite.
  • A DatabaseHelper class centralizes database operations like creating, opening, and managing tables.
  • You can perform standard CRUD (Create, Read, Update, Delete) operations using insert, query, update, and delete methods.
  • Using a data model class (like Item) simplifies mapping data between Dart objects and database rows.

This knowledge is crucial for building robust Flutter apps with local data persistence!

常见问题解答

「集成 SQLite 数据库」课时是免费的吗？

是的 — 「集成 SQLite 数据库」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Flutter Mobile Development 课程的其余内容，请升级到 CoddyKit PRO。 Flutter Mobile Development 课程共包含 4 节课。

「集成 SQLite 数据库」这节课中我会学到什么？

使用 `sqflite` 软件包将 SQLite 数据库集成到 Flutter 应用中，以存储结构化的关系数据。 你通过在浏览器中直接运行的动手代码来练习 Flutter Mobile Development，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Flutter Mobile Development 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Flutter Mobile Development 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 2 节课，共 4 节。

「集成 SQLite 数据库」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Flutter Mobile Development 课中编写并运行代码吗？

能。每节 Flutter Mobile Development 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

此课程中的所有课时

  1. 使用共享偏好存储数据
  2. 集成 SQLite 数据库
  3. 文件系统操作
  4. Hive 与 NoSQL 本地存储
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