如何在Flutter中使用SQFlite进行数据库插入 [英] How to do a database insert with SQFlite in Flutter

问题描述

如何使用SQFlite插件将数据插入Flutter中的数据库中？

那里有很多问题解决问题，但我找不到添加一个规范的答案。我的答案如下。

解决方案

添加依赖项

打开 pubspec.yaml 并在依赖项部分添加以下行：

  sqflite ：^ 1.0.0 
 path_provider：^ 0.4.1 
  

sqflite 是

为方便您复制和粘贴，以下是 main.dart ：

  import'package：flutter / material.dart'; 
 import‘package：flutter_db_operations / database_helper.dart’; 
导入 package：sqflite / sqflite.dart； 
 
 void main（）=> runApp（MyApp（））; 
 
类MyApp扩展了StatelessWidget {
 @override 
 Widget build（BuildContext context）{
 return MaterialApp（
 title：'SQFlite Demo'，
主题：ThemeData（
 primarySwatch：Colors.blue，
），
主页：MyHomePage（），
）； 
} 
} 
 
类MyHomePage扩展了StatelessWidget {
 
 @override 
 Widget build（BuildContext context）{
 return Scaffold （
 appBar：AppBar（
标题：Text（'sqflite'），
），
正文：RaisedButton（
子项：Text（'insert'，style： TextStyle（fontSize：20），），
 onPressed：（）{_insert（）;}，
），
）; 
} 
 
 _insert（）async {
 
 //获取对数据库
的引用//因为这是一个昂贵的操作，我们使用async和await 
数据库db = await DatabaseHelper.instance.database; 
 
 //要插入
的行Map< String，dynamic> row = {
 DatabaseHelper.columnName：'Bob'，
 DatabaseHelper.columnAge：23 
}; 
 
 //进行插入并获取插入行的ID 
 int id =等待db.insert（DatabaseHelper.table，row）; 
 
 //原始插入
 // 
 //字符串名称= Bob； 
 // int age = 23; 
 // int id =等待db.rawInsert（
 //'INSERT INTO $ {DatabaseHelper.table}'
 //'（$ {DatabaseHelper.columnName}，$ {DatabaseHelper.columnAge }}'
 //'VALUES（?,？）'，[name，age]）; 
 
 print（等待db.query（DatabaseHelper.table））; 
} 
 
} 
  





继续

• 这篇文章是我上一篇文章的发展： Flutter中的简单SQFlite数据库示例。有关其他SQL操作和建议，请参见该帖子。

How do you insert data into a database in Flutter using the SQFlite plugin?

There are a number of problem solving questions out there but none that I could find to add a canonical answer to. My answer is below.

解决方案

Add the dependencies

Open pubspec.yaml and in the dependency section add the following lines:

sqflite: ^1.0.0
path_provider: ^0.4.1

The sqflite is the SQFlite plugin of course and the path_provider will help us get the user directory on Android and iPhone.

Make a database helper class

I'm keeping a global reference to the database in a singleton class. This will prevent concurrency issues and data leaks (that's what I hear, but tell me if I'm wrong). You can also add helper methods (like insert) in here for accessing the database.

Create a new file called database_helper.dart and paste in the following code:

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
          )
          ''');
  }
}

Insert data

We'll use an async method to do our insert:

  _insert() 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 insert
    Map<String, dynamic> row = {
      DatabaseHelper.columnName : 'Bob',
      DatabaseHelper.columnAge  : 23
    };

    // do the insert and get the id of the inserted row
    int id = await db.insert(DatabaseHelper.table, row);

    // show the results: print all rows in the db
    print(await db.query(DatabaseHelper.table));
  }

Notes

• You will have to import the DatabaseHelper class and sqflite if you are in another file (like main.dart).
• The SQFlite plugin uses a Map<String, dynamic> to map the column names to the data in each row.
• We didn't specify the id. SQLite auto increments it for us.

Raw insert

SQFlite also supports doing a raw insert. This means that you can use a SQL string. Lets insert the same row again using rawInsert().

db.rawInsert('INSERT INTO my_table(name, age) VALUES("Bob", 23)');

Of course, we wouldn't want to hard code those values into the SQL string, but we also wouldn't want to use interpelation like this:

String name = 'Bob';
int age = 23;
db.rawInsert('INSERT INTO my_table(name, age) VALUES($name, $age)'); // Dangerous!

That would open us up to SQL injection attacks. Instead we can use data binding like this:

db.rawInsert('INSERT INTO my_table(name, age) VALUES(?, ?)', [name, age]);

The [name, age] are filled in for the question mark placeholders in (?, ?). The table and column names are safer to use interpelation for, so we could do this finally:

String name = 'Bob';
int age = 23;
db.rawInsert(
    'INSERT INTO ${DatabaseHelper.table}'
        '(${DatabaseHelper.columnName}, ${DatabaseHelper.columnAge}) '
        'VALUES(?, ?)', [name, age]);

Supplemental code

For your copy-and-paste convenience, here is the layout code for main.dart:

import 'package:flutter/material.dart';
import 'package:flutter_db_operations/database_helper.dart';
import 'package:sqflite/sqflite.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'SQFlite Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('sqflite'),
      ),
      body: RaisedButton(
        child: Text('insert', style: TextStyle(fontSize: 20),),
        onPressed: () {_insert();},
      ),
    );
  }

  _insert() 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 insert
    Map<String, dynamic> row = {
      DatabaseHelper.columnName : 'Bob',
      DatabaseHelper.columnAge  : 23
    };

    // do the insert and get the id of the inserted row
    int id = await db.insert(DatabaseHelper.table, row);

    // raw insert
    //
    //  String name = 'Bob';
    //  int age = 23;
    //  int id = await db.rawInsert(
    //    'INSERT INTO ${DatabaseHelper.table}'
    //          '(${DatabaseHelper.columnName}, ${DatabaseHelper.columnAge}) '
    //          'VALUES(?, ?)', [name, age]);

    print(await db.query(DatabaseHelper.table));
  }

}

Going on

• This post is a development from my previous post: Simple SQFlite database example in Flutter. See that post for other SQL operations and advice.

这篇关于如何在Flutter中使用SQFlite进行数据库插入的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！