Project: Mini REST API Backend in Dart

Project Goal

Build a complete REST API backend in Dart using the shelf framework. The API manages a product catalog with full CRUD, JSON responses, validation, error handling, and request logging. This capstone project combines everything you've learned in this course.

Architecture

• Model: Product with validation
• Repository: In-memory store with CRUD
• Controller: Route handlers
• Middleware: CORS + request logging
• Server: Shelf + shelf_router

# pubspec.yaml
dependencies:
  shelf: ^1.4.0
  shelf_router: ^1.1.0

Full Code

import 'dart:convert';
import 'dart:io';
import 'package:shelf/shelf.dart';
import 'package:shelf/shelf_io.dart' as io;
import 'package:shelf_router/shelf_router.dart';

// ── Model ───────────────────────────────────────────────
class Product {
  final int id;
  final String name;
  final double price;
  final String category;
  final int stock;

  Product({required this.id, required this.name, required this.price,
           required this.category, required this.stock});

  factory Product.fromJson(Map<String, dynamic> j, {int? id}) => Product(
    id: id ?? j['id'] ?? 0,
    name: j['name'] as String,
    price: (j['price'] as num).toDouble(),
    category: j['category'] as String,
    stock: j['stock'] as int? ?? 0,
  );

  Map<String, dynamic> toJson() => {
    'id': id, 'name': name, 'price': price, 'category': category, 'stock': stock,
  };
}

// ── Repository ─────────────────────────────────────────
class ProductRepository {
  final Map<int, Product> _db = {};
  int _nextId = 1;

  List<Product> getAll({String? category}) {
    var products = _db.values;
    if (category != null) products = products.where((p) => p.category == category);
    return products.toList()..sort((a, b) => a.id.compareTo(b.id));
  }

  Product? getById(int id) => _db[id];

  Product create(Map<String, dynamic> data) {
    var p = Product.fromJson(data, id: _nextId++);
    _db[p.id] = p;
    return p;
  }

  Product? update(int id, Map<String, dynamic> data) {
    if (!_db.containsKey(id)) return null;
    var updated = Product.fromJson({'id': id, ...data});
    _db[id] = updated;
    return updated;
  }

  bool delete(int id) {
    if (!_db.containsKey(id)) return false;
    _db.remove(id);
    return true;
  }
}

// ── Helpers ────────────────────────────────────────────
Response json(dynamic data, {int status = 200}) => Response(
  status,
  body: jsonEncode(data),
  headers: {'Content-Type': 'application/json; charset=utf-8'},
);

Response error(String message, {int status = 400}) =>
    json({'error': message, 'status': status}, status: status);

// ── Controller ────────────────────────────────────────
class ProductController {
  final ProductRepository _repo;
  ProductController(this._repo);

  Response getAll(Request req) {
    var cat = req.url.queryParameters['category'];
    var products = _repo.getAll(category: cat);
    return json({'data': products.map((p) => p.toJson()).toList(), 'count': products.length});
  }

  Response getById(Request req, String id) {
    var product = _repo.getById(int.tryParse(id) ?? -1);
    return product != null ? json(product.toJson()) : error('Product not found', status: 404);
  }

  Future<Response> create(Request req) async {
    try {
      var body = jsonDecode(await req.readAsString()) as Map<String, dynamic>;
      if (body['name'] == null || body['price'] == null || body['category'] == null) {
        return error('name, price, and category are required');
      }
      var p = _repo.create(body);
      return json(p.toJson(), status: 201);
    } on FormatException {
      return error('Invalid JSON');
    }
  }

  Future<Response> update(Request req, String id) async {
    try {
      var body = jsonDecode(await req.readAsString()) as Map<String, dynamic>;
      var p = _repo.update(int.tryParse(id) ?? -1, body);
      return p != null ? json(p.toJson()) : error('Product not found', status: 404);
    } on FormatException {
      return error('Invalid JSON');
    }
  }

  Response delete(Request req, String id) {
    return _repo.delete(int.tryParse(id) ?? -1)
        ? json({'message': 'Deleted', 'id': int.parse(id)})
        : error('Product not found', status: 404);
  }
}

// ── Server ────────────────────────────────────────────
void main() async {
  var repo = ProductRepository();
  // Seed data
  repo.create({'name': 'Dart Programming Book', 'price': 39.99, 'category': 'books', 'stock': 50});
  repo.create({'name': 'Flutter Widget Catalog', 'price': 29.99, 'category': 'books', 'stock': 30});
  repo.create({'name': 'Mechanical Keyboard', 'price': 89.99, 'category': 'electronics', 'stock': 15});

  var ctrl = ProductController(repo);
  var router = Router()
    ..get('/products', ctrl.getAll)
    ..get('/products/<id>', ctrl.getById)
    ..post('/products', ctrl.create)
    ..put('/products/<id>', ctrl.update)
    ..delete('/products/<id>', ctrl.delete)
    ..get('/health', (req) => json({'status': 'ok', 'time': DateTime.now().toIso8601String()}));

  var handler = Pipeline()
      .addMiddleware(logRequests())
      .addHandler(router.call);

  var server = await io.serve(handler, 'localhost', 8080);
  print('Product API running on http://localhost:$${server.port}');
  print('  GET    /products');
  print('  GET    /products?category=books');
  print('  GET    /products/1');
  print('  POST   /products');
  print('  PUT    /products/1');
  print('  DELETE /products/1');
}

Testing the API

# Get all products
curl http://localhost:8080/products

# Filter by category
curl http://localhost:8080/products?category=books

# Get one product
curl http://localhost:8080/products/1

# Create a product
curl -X POST http://localhost:8080/products \
  -H "Content-Type: application/json" \
  -d '{"name":"USB Hub","price":24.99,"category":"electronics","stock":100}'

# Update
curl -X PUT http://localhost:8080/products/1 \
  -H "Content-Type: application/json" \
  -d '{"name":"Dart Book 2nd Ed","price":44.99,"category":"books","stock":40}'

# Delete
curl -X DELETE http://localhost:8080/products/4

Challenges

• Add JWT authentication middleware
• Persist products to a JSON file or SQLite database
• Add pagination (?page=1&limit=10)
• Add input validation with a schema validator
• Write integration tests using the Dart test package and shelf_test
• Deploy to a VPS using dart compile exe