Dart 如何在flatter中使用SQFlite更新数据库表

添加依赖项

打开pubspec.yaml，然后在Dependency部分中添加以下行:

sqflite: ^1.0.0
path_provider: ^0.4.1

sqflite当然是SQFlite插件，path_provider插件将帮助我们获得Android和iPhone上的用户目录.

创建数据库帮助器类

我在一个单例类中保存了对数据库的全局引用.这将防止并发问题和数据泄漏(这是我听说的，如果我说错了，请告诉我).您还可以在这里添加助手方法(如UPDATE)来访问数据库.

创建一个名为database_helper.dart的新文件，并按以下代码粘贴:

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
          )
          ''');
  }
}

更新行

首先让我们看一下insert a row，这样我们就有一些东西需要更新:

  _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));
  }

然后是如何进行更新:

  _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));
  }

注意事项

• 如果你在另一个文件(比如main.dart)中，你必须导入DatabaseHelper类和sqflite类.
• SQFlite插件使用Map<String, dynamic>将列名映射到每行中的数据.

原始更新

SQFlite还支持执行原始更新.这意味着您可以使用SQL字符串.让我们使用rawUpdate()再次更新同一行.

int updateCount = await db.rawUpdate('''
    UPDATE my_table 
    SET name = ?, age = ? 
    WHERE _id = ?
    ''', 
    ['Susan', 13, 1]);

末尾括号中的项目绑定到SQL字符串中的?个问号.您可以使用插值来填充表和列名，但是由于SQL注入攻击的危险，您不应该对这些值使用插值.

int updateCount = await db.rawUpdate('''
    UPDATE ${DatabaseHelper.table} 
    SET ${DatabaseHelper.columnName} = ?, ${DatabaseHelper.columnAge} = ? 
    WHERE ${DatabaseHelper.columnId} = ?
    ''',
    ['Susan', 13, 1]);