从单独的文件在main.dart中使用SQLite

Question

我遵循了flutter文档中的这个简单示例。然而，这是在一个单独的文件(db_test.db(中编写的。我的目标是在某个时候将数据转换为ListView。那么，我该如何使用CRUD操作，比如在main.dart中检索数据呢？我可以把它添加到我的main.dart文件中，但我想保持它的干净和独立。

官方长笛教程

我的db.dart文件

void main () async {
final database = openDatabase(
join(await getDatabasesPath(), 'to_do.db'),
onCreate: (db, version) {
return db.execute("CREATE TABLE tasks(id INTEGER PRIMARY KEY, title TEXT, created TEXT, INTEGER is_complete)");
},
version: 1,
);
Future<void> insertTask (Task task) async {
final Database db = await database;
await db.insert(
'tasks',
task.toMap(),
conflictAlgorithm: ConflictAlgorithm.replace
);
}
Future<List<Task>> tasks () async {
final Database db = await database;
final List<Map<String, dynamic>> maps = await db.query('tasks');
return List.generate(maps.length, (i) {
return Task(
id: maps[i]['id'],
title: maps[i]['title'],
created: maps[i]['created'],
isComplete: maps[i]['is_complete']
);
});
}
Future<void> updateTask(Task task) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'tasks',
task.toMap(),
// Ensure that the Dog has a matching id.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [task.id],
);
}
Future<void> deleteTask(int id) async {
// Get a reference to the database.
final db = await database;
// Remove the Dog from the database.
await db.delete(
'tasks',
// Use a `where` clause to delete a specific dog.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [id],
);
}
}

Answer 1

您可以创建一个包含class和静态成员的新文件来提供帮助。静态成员确保在整个应用程序中只创建一个数据库实例。

class DatabaseHelper {
static Database _database;
///Returns db instance if already opened
///else call the initDatabase
static Future<Database> getDBConnector() async {
if (_database != null) {
return _database;
}
return await _initDatabase();
}
///Open DB Connection, returns a Database instance.
///
static Future<Database> _initDatabase() async {
_database = await openDatabase(
join(await getDatabasesPath(), "my_path.db"),
onCreate: (db, version) async {
//on create
},
version: 1,
);
return _database;
}
//put your CRUD in static function
static Future<void> insertTask (Task task) async {
final Database db = await getDBConnector();
await db.insert(
'tasks',
task.toMap(),
conflictAlgorithm: ConflictAlgorithm.replace
);
}
//the same with edit, delete
}

然后在你的另一个文件(比如main.dart(中，你可以这样称呼它：

import "./databaseHelper.dart";
void caller() async{
//create task
//insert
await DatabaseHelper.insertTask(task);
}

请确保调用方是异步的。