flutter中的Sqflite创建表失败

Question

我是flutter的新手，我试图创建一个数据库来处理用户，所以我编写了以下数据库服务类

import 'package:banking_system/database/transfer_db.dart';
import 'package:banking_system/database/user_db.dart';
import 'package:flutter/widgets.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart';

import '../models/user.dart';

class UserDatabaseService {
  static const _databaseName = "userbankingdb.db";
  static const _databaseVersion = 1;
  final tableName = "users";


  UserDatabaseService._privateConstructor();
  static final UserDatabaseService _instance = UserDatabaseService._privateConstructor();
  factory UserDatabaseService() => _instance;

   Database? _db;

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

  }

  // this opens the database (and creates it if it doesn't exist)
  Future<Database> init() async {

    final documentsDirectory = await getApplicationDocumentsDirectory();
    final path = join(documentsDirectory.path, _databaseName);
    _db = await openDatabase(
      path,
      version: _databaseVersion,
      onCreate: (db, version) async{
        await createUserTable(db);
      },
    );

    print(_db!.path);
    return _db!;
  }

  // SQL code to create the database table



  Future<void> createUserTable(Database database) async{
    print("in create user table");

    await database.query("""CREATE TABLE IF NOT EXISTS "${tableName}"(
    "user_id"   INTEGER NOT NULL,
    "name"  TEXT NOT NULL,
    "email" TEXT NOT NULL,
    "password"  TEXT NOT NULL,
    "gender"    TEXT NOT NULL,
    "balance"   REAL NOT NULL, 
    PRIMARY KEY("user_id" AUTOINCREMENT)
);""");

print("The last inserted row id is ");
print(await createUser(name: "Farida Yasser", email: "[email protected]", password: "12345abcd", gender: "female", balance: 3200));


  }

  Future<int> createUser({required String name, required String email, required String password, required String gender, required double balance}) async{
    final Database database = await  UserDatabaseService().database;
    return await database.rawInsert(
        '''INSERT INTO $tableName (name, email, password, gender,  balance) VALUES (?,?,?,?,?)''',
        [name, email, password, gender, balance.toString()]
    );
  }

  Future<List<User>> fetchAllUsers() async{
    final Database database = await  UserDatabaseService().database;
    final users = await database.rawQuery('''SELECT * FROM $tableName''');
    return users.map((eachUserMap) => User.fromSqfliteDatabase(eachUserMap)).toList();

  }

  Future<User> fetchUserById(int userId) async{
    final Database database = await UserDatabaseService().database;
    final user = await database.rawQuery('''SELECT * FROM $tableName WHERE user_id = ?''', [userId.toString()]);
    return User.fromSqfliteDatabase(user.first);
  }

  Future<int> updateUserBalance(int userId, double changeInBalance) async{
    final user = await fetchUserById(userId);
    double newAmount = user.balance + changeInBalance;
    final database = await  UserDatabaseService().database;
    return await database.update(tableName, {'balance': newAmount}, where: "user_id = ?", whereArgs: [userId]);
  }




}

此函数在以下主屏幕小部件中调用

import 'package:banking_system/constants/textstyles.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

import '../database/user_db.dart';
import '../models/user.dart';

class HomeScreen extends StatefulWidget {
  final Future<User> currentUser;
   HomeScreen({Key? key, required this.currentUser}) : super(key: key);

  @override
  State<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title:Text("Home Page"),
        titleTextStyle: appbarTitleTextStyle,
      ),
      body: FutureBuilder(
        future: widget.currentUser,
        builder: (context, snapshot) {
          if(snapshot.connectionState == ConnectionState.waiting){
            return Center(child: CircularProgressIndicator(),);
          }
          if(snapshot.hasError){
            print(snapshot.error);
          }
          if(!snapshot.hasData){
            return Center(
              child: Text("User was not found")

              ,);
          }else{
            User currentUserData = snapshot.data!;
            return  SafeArea(child: Column(
              children: [
                Image.asset(currentUserData.gender == "female" ? "images/woman.png" : "images/man.png"),
                Text("Hello " + currentUserData.name),
                Text("Your email address is: " + currentUserData.email),
                Text("Yor Current Balance is: " + currentUserData.balance.toString()),

              ],
            ));
          }
        },
      )
    );
  }
}

它会产生这些错误

D/hw-ProcessState(24928): Binder ioctl to enable oneway spam detection failed: Invalid argument
E/OpenGLRenderer(24928): fbcNotifyFrameComplete error: undefined symbol: fbcNotifyFrameComplete
E/OpenGLRenderer(24928): fbcNotifyNoRender error: undefined symbol: fbcNotifyNoRender
D/DecorView[](24928): onWindowFocusChanged hasWindowFocus true
E/BLASTBufferQueue(24928): [SurfaceView[com.example.banking_system/com.example.banking_system.MainActivity]#1](f:0,a:2) isEGL=1, mPendingRelease.size()=1, mMaxAcquiredBuffers=4, currentMaxAcquiredBufferCount=2
I/flutter (24928): /data/user/0/com.example.banking_system/app_flutter/userbankingdb.db
I/flutter (24928): type 'int' is not a subtype of type 'String'
E/BLASTBufferQueue(24928): [SurfaceView[com.example.banking_system/com.example.banking_system.MainActivity]#1](f:0,a:4) isEGL=1, mPendingRelease.size()=2, mMaxAcquiredBuffers=4, currentMaxAcquiredBufferCount=2

需要注意的是，createUserTable 中 print 语句的结果没有出现在控制台上，而且 fetchUserById 函数也返回 null。

我只是想知道我的代码可能有什么问题。

Answer 1

第 1 步：使用等待数据库。execute("""CREATE TABLE IF NOT EXISTS "${tableName}" 不是等待数据库。query("""CREATE TABLE IF NOT EXISTS "${tableName}"

第2步：移动这一行print（await createUser（名称：“Farida Yasser”，电子邮件：“[email protected]”，密码：“12345abcd”，性别：“女”，余额：3200））;从 Future createUserTable 到 Init()

第3步：考虑数据类型“balance”REAL NOT NULL和balance.toString()，如果数据库已在Android模拟器中创建，您可以使用Device Explorer将其删除；

测试结果