how to build a data base of user in flutter dart code example

Example 1: delete query in sqlite flutter

// Get a location using getDatabasesPath
var databasesPath = await getDatabasesPath();
String path = join(databasesPath, 'demo.db');

// Delete the database
await deleteDatabase(path);

// open the database
Database database = await openDatabase(path, version: 1,
    onCreate: (Database db, int version) async {
  // When creating the db, create the table
  await db.execute(
      'CREATE TABLE Test (id INTEGER PRIMARY KEY, name TEXT, value INTEGER, num REAL)');
});

// Insert some records in a transaction
await database.transaction((txn) async {
  int id1 = await txn.rawInsert(
      'INSERT INTO Test(name, value, num) VALUES("some name", 1234, 456.789)');
  print('inserted1: $id1');
  int id2 = await txn.rawInsert(
      'INSERT INTO Test(name, value, num) VALUES(?, ?, ?)',
      ['another name', 12345678, 3.1416]);
  print('inserted2: $id2');
});

// Update some record
int count = await database.rawUpdate(
    'UPDATE Test SET name = ?, value = ? WHERE name = ?',
    ['updated name', '9876', 'some name']);
print('updated: $count');

// Get the records
List<Map> list = await database.rawQuery('SELECT * FROM Test');
List<Map> expectedList = [
  {'name': 'updated name', 'id': 1, 'value': 9876, 'num': 456.789},
  {'name': 'another name', 'id': 2, 'value': 12345678, 'num': 3.1416}
];
print(list);
print(expectedList);
assert(const DeepCollectionEquality().equals(list, expectedList));

// Count the records
count = Sqflite
    .firstIntValue(await database.rawQuery('SELECT COUNT(*) FROM Test'));
assert(count == 2);

// Delete a record
count = await database
    .rawDelete('DELETE FROM Test WHERE name = ?', ['another name']);
assert(count == 1);

// Close the database
await database.close();

Example 2: sglite offline in flutter

import 'dart:async';

import 'package:flutter/widgets.dart';

import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';

void main() async {
  // Avoid errors caused by flutter upgrade.
  // Importing 'package:flutter/widgets.dart' is required.
  WidgetsFlutterBinding.ensureInitialized();
  // Open the database and store the reference.
  final Future<Database> database = openDatabase(
    // Set the path to the database. Note: Using the `join` function from the
    // `path` package is best practice to ensure the path is correctly
    // constructed for each platform.
    join(await getDatabasesPath(), 'doggie_database.db'),
    // When the database is first created, create a table to store dogs.
    onCreate: (db, version) {
      return db.execute(
        "CREATE TABLE dogs(id INTEGER PRIMARY KEY, name TEXT, age INTEGER)",
      );
    },
    // Set the version. This executes the onCreate function and provides a
    // path to perform database upgrades and downgrades.
    version: 1,
  );

  Future<void> insertDog(Dog dog) async {
    // Get a reference to the database.
    final Database db = await database;

    // Insert the Dog into the correct table. Also specify the
    // `conflictAlgorithm`. In this case, if the same dog is inserted
    // multiple times, it replaces the previous data.
    await db.insert(
      'dogs',
      dog.toMap(),
      conflictAlgorithm: ConflictAlgorithm.replace,
    );
  }

  Future<List<Dog>> dogs() async {
    // Get a reference to the database.
    final Database db = await database;

    // Query the table for all The Dogs.
    final List<Map<String, dynamic>> maps = await db.query('dogs');

    // Convert the List<Map<String, dynamic> into a List<Dog>.
    return List.generate(maps.length, (i) {
      return Dog(
        id: maps[i]['id'],
        name: maps[i]['name'],
        age: maps[i]['age'],
      );
    });
  }

  Future<void> updateDog(Dog dog) async {
    // Get a reference to the database.
    final db = await database;

    // Update the given Dog.
    await db.update(
      'dogs',
      dog.toMap(),
      // Ensure that the Dog has a matching id.
      where: "id = ?",
      // Pass the Dog's id as a whereArg to prevent SQL injection.
      whereArgs: [dog.id],
    );
  }

  Future<void> deleteDog(int id) async {
    // Get a reference to the database.
    final db = await database;

    // Remove the Dog from the database.
    await db.delete(
      'dogs',
      // Use a `where` clause to delete a specific dog.
      where: "id = ?",
      // Pass the Dog's id as a whereArg to prevent SQL injection.
      whereArgs: [id],
    );
  }

  var fido = Dog(
    id: 0,
    name: 'Fido',
    age: 35,
  );

  // Insert a dog into the database.
  await insertDog(fido);

  // Print the list of dogs (only Fido for now).
  print(await dogs());

  // Update Fido's age and save it to the database.
  fido = Dog(
    id: fido.id,
    name: fido.name,
    age: fido.age + 7,
  );
  await updateDog(fido);

  // Print Fido's updated information.
  print(await dogs());

  // Delete Fido from the database.
  await deleteDog(fido.id);

  // Print the list of dogs (empty).
  print(await dogs());
}

class Dog {
  final int id;
  final String name;
  final int age;

  Dog({this.id, this.name, this.age});

  Map<String, dynamic> toMap() {
    return {
      'id': id,
      'name': name,
      'age': age,
    };
  }

  // Implement toString to make it easier to see information about
  // each dog when using the print statement.
  @override
  String toString() {
    return 'Dog{id: $id, name: $name, age: $age}';
  }
}