问题描述
我有一个名为(async () => {
const sub = await stripe.subscriptions.retrieve('sub_HurxwcQoCIH7jv')
console.log(sub) //
})()
的文件。该文件具有使用各种方法的类。第一种方法打开数据库并存储引用，而其他方法对该数据库进行包含，更新和删除。问题在于其他方法无法看到第一种方法创建的数据库。我想念什么？
代码如下：
const functionWithSomeName = async () => {
const sub = await ...CODE HERE...
console.log(sub)
}
functionWithSomeName()
解决方法
database变量仅存储在initDatabase方法中，而不存储在DatabaseServices类中，这意味着只能从initDatabase方法进行访问。 / p>
下面的代码示例显示如何将database作为属性存储在DatabaseServices类上，以允许该类内的所有方法使用它。
class DatabaseServices {
Future<Database> _db;
Future<void> initDatabase() async {
// Open the database and store the reference.
_db = openDatabase(
// Set the path to the database.
join(await getDatabasesPath(),'counter_database.db'),// When the database is first created,create a table to store counters;
onCreate: (db,version) {
// Run the CREATE TABLE statement on the database.
return db.execute(
"CREATE TABLE counters(id INTEGER PRIMARY KEY,name TEXT,value INTEGER)",);
},// Set the version. This executes the onCreate function and provides a
// path to perform database upgrades and downgrades.
version: 1,);
}
// Define a function that inserts counters into the database.
Future<void> insertCounter(Counter counter) async {
// Get a reference to the database.
final db = await _db;
// Insert the Counter into the correct table. Here,if a counter is inserted twice,// it replace any previous data.
await db.insert(
'counters',counter.toMap(),conflictAlgorithm: ConflictAlgorithm.replace,);
}
// A method that retrieves all the counters from the counters table.
Future<List<Counter>> counters() async {
// Get a reference to the database.
final db = await _db;
// Query the table for all the Counters.
final List<Map<String,dynamic>> maps = await db.query('counters');
// Counvert the List<Map<String,dynamic>> into a List<Counter>
return List.generate(maps.length,(i) {
return Counter(
id: maps[i]['id'],name: maps[i]['name'],value: maps[i]['value'],);
});
}
// Method to update a Counter in the database
Future<void> updateCounter(Counter counter) async {
final db = await _db;
await db.update(
'counters',where: "id = ?",whereArgs: [counter.id],);
}
//Delete a Counter from the database
Future<void> deleteCounter(int id) async {
final db = await _db;
await db.delete(
'counters',whereArgs: [id],);
}
}
您可以找到有关打开数据库here的更多信息。