打开pubspec.yaml
并在依赖项部分中添加以下行:
sqflite: ^1.0.0
path_provider: ^0.4.1
该sqflite
是SQFlite当然插件和path_provider
将帮助我们在Android和iPhone用户目录。
我在单例类中保持对数据库的全局引用。这将防止并发问题和数据泄漏(这是我所听到的,但请告诉我是否错误)。您还可以在此处添加用于访问数据库的辅助方法(例如update)。
创建一个名为database_helper.dart的新文件,并粘贴以下代码:
import 'dart:io' show Directory;
import 'package:path/path.dart' show join;
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart' show getApplicationDocumentsDirectory;
class DatabaseHelper {
static final _databaseName = "MyDatabase.db";
static final _databaseVersion = 1;
static final table = 'my_table';
static final columnId = '_id';
static final columnName = 'name';
static final columnAge = 'age';
// 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 {
if (_database != null) return _database;
// lazily instantiate the db the first time it is accessed
_database = await _initDatabase();
return _database;
}
// this opens the database (and creates it 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,
$columnName TEXT NOT NULL,
$columnAge INTEGER NOT NULL
)
''');
}
}
首先让我们插入一行,以便我们进行更新:
_insert() async {
Database db = await DatabaseHelper.instance.database;
Map<String, dynamic> row = {
DatabaseHelper.columnName : 'Bob',
DatabaseHelper.columnAge : 23
};
int id = await db.insert(DatabaseHelper.table, row);
print(await db.query(DatabaseHelper.table));
}
然后,这是执行更新的方法:
_update() async {
// get a reference to the database
// because this is an expensive operation we use async and await
Database db = await DatabaseHelper.instance.database;
// row to update
Map<String, dynamic> row = {
DatabaseHelper.columnName : 'Mary',
DatabaseHelper.columnAge : 32
};
// We'll update the first row just as an example
int id = 1;
// do the update and get the number of affected rows
int updateCount = await db.update(
DatabaseHelper.table,
row,
where: '${DatabaseHelper.columnId} = ?',
whereArgs: [id]);
// show the results: print all rows in the db
print(await db.query(DatabaseHelper.table));
}
笔记
DatabaseHelper
,sqflite
则必须导入该类。Map<String, dynamic>
来将列名映射到每一行中的数据。SQFlite还支持进行原始更新。这意味着您可以使用SQL字符串。让我们再次使用更新同一行rawUpdate()
。
int updateCount = await db.rawUpdate('''
UPDATE my_table
SET name = ?, age = ?
WHERE _id = ?
''',
['Susan', 13, 1]);
末尾方括号中的项目绑定到?
SQL字符串中的问号。您可以使用插值法来填充表和列名,但是由于存在SQL注入攻击的危险,因此不应对值使用插值法。
int updateCount = await db.rawUpdate('''
UPDATE ${DatabaseHelper.table}
SET ${DatabaseHelper.columnName} = ?, ${DatabaseHelper.columnAge} = ?
WHERE ${DatabaseHelper.columnId} = ?
''',
['Susan', 13, 1]);
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我来说两句