How to initialize SQLite connection - flutter

Question

I new in Flutter.
I have already exist db and need add it to app.
Put file in assets/db/sms.db
in file pubspec.yaml
assets:
- assets/db/sms.db
Copy db file in applicationDirectory.
In file categoriesList.dart I try connect to it.
SmsDataBaseHelper.instance.getAllCategories()
I get error message.
database_helper.dart
import 'package:flutter/services.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path/path.dart' as path;
import 'package:path_provider/path_provider.dart';
import 'dart:io' as io;
import '/models/categories.dart';
class SmsDataBaseHelper {
static final SmsDataBaseHelper instance = SmsDataBaseHelper._();
static Database? _db;
SmsDataBaseHelper._();
Future<Database> get db async {
_db ??= await _init();
return _db!;
}
Future<Database> _init() async {
io.Directory applicationDirectory = await getApplicationDocumentsDirectory();
String dbPathSms = path.join(applicationDirectory.path, "sms.db");
bool dbExistsSms = await io.File(dbPathSms).exists();
if (!dbExistsSms) {
// Copy from asset
ByteData data = await rootBundle.load(path.join("assets", "db", "sms.db"));
List<int> bytes = data.buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);
// Write and flush the bytes written
await io.File(dbPathSms).writeAsBytes(bytes, flush: true);
}
return await openDatabase(dbPathSms);
}
/// get all the words from categories
Future<List<Categories>> getAllCategories() async {
if (_db == null) {
throw "_db is not initiated, initiate using [init(db)] function";
}
List<Map>? categories;
await _db!.transaction((txn) async {
categories = await txn.query(
"categories",
columns: [
"name",
"ru",
],
);
});
return categories!.map((e) => Categories.fromJson(e as Map<String, dynamic>)).toList();
}
}
categoriesList.dart
import 'package:flutter/material.dart';
import 'package:sqflite/sqflite.dart';
import '../utils/database_helper.dart';
import '../models/categories.dart';
class CategoriesList extends StatefulWidget {
const CategoriesList({super.key});
#override
State<CategoriesList> createState() => _CategoriesListState();
}
class _CategoriesListState extends State<CategoriesList> {
//late List<Categories> categoriesList;
#override
void initState(){
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('SMS Home Page'),
),
body: FutureBuilder<List<Categories>>(
future: SmsDataBaseHelper.instance.getAllCategories(),
builder: (BuildContext context, AsyncSnapshot<List<Categories>> snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none:
return const Text('start widget');
case ConnectionState.active:
case ConnectionState.waiting:
return const Text('Awaiting result from api...');
case ConnectionState.done:
if (snapshot.hasError)
return Text('Error: ${snapshot.error}');
return Text('Result: ${snapshot.data}');
}
},
),
);
}
}

Answer 1

use this class to build database ..
import 'package:sqflite/sqflite.dart';
import 'package:path/path.dart';
class SqlDb {
static Database? _db;
Future<Database?> get db async {
if (_db == null) {
_db = await initialDb();
return _db;
} else {
return _db;
}
}
initialDb() async {
String databasepath = await getDatabasesPath();
String path = join(databasepath, 'shop.db');
Database mydb = await openDatabase(path,
onCreate: _onCreate, version: 1, onUpgrade: _onUpgrade);
return mydb;
}
_onUpgrade(Database db, int oldversion, int newversion) async {}
deletemydatabase() async {
String databasepath = await getDatabasesPath();
String path = join(databasepath, 'shop.db');
var x = await deleteDatabase(path);
return x;
}
_onCreate(Database db, int version) async {
await db.execute(
"CREATE TABLE cart (id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT , title TEXT, size TEXT , code TEXT , img TEXT , price TEXT )");
}
//Select
readData(String sql) async {
Database? mydb = await db;
List<Map> response = await mydb!.rawQuery(sql);
return response;
}
//insert data
insertData(String sql) async {
Database? mydb = await db;
int response = await mydb!.rawInsert(sql);
return response;
}
deleteData(String sql) async {
Database? mydb = await db;
int response = await mydb!.rawDelete(sql);
return response;
}
updateData(String sql) async {
Database? mydb = await db;
int response = await mydb!.rawUpdate(sql);
return response;
}
}