# Application Type Scorecard Web Application: Server-Side Rendering Required: Yes: +3 MVC No: 0 SEO Critical: Yes: +3 MVC No: 0 Progressive Enhancement Needed: Yes: +2 MVC No: 0 Desktop Application: Rich UI Interactions: Yes: +3 MVVM No: 0 Offline Capability: Yes: +3 MVVM No: 0 Native Platform Integration: Yes: +2 MVVM No: 0 Mobile Application: Cross-Platform: Yes: +2 Hybrid No: 0 Real-Time Updates: Yes: +2 MVVM No: 0 Offline-First: Yes: +3 MVVM No: 0 API/Microservice: RESTful Design: Yes: +3 MVC No: 0 Stateless Operations: Yes: +3 MVC No: 0 GraphQL: Yes: +1 Hybrid No: 0 

public class ArchitectureDecisionHelper { public ArchitectureRecommendation AnalyzeDataFlow(ProjectRequirements requirements) { var score = new ArchitectureScore(); // Analyze data flow patterns if (requirements.DataFlow.IsPrimarilyRequestResponse) score.MVC += 3; if (requirements.DataFlow.HasComplexStateManagement) score.MVVM += 3; if (requirements.DataFlow.RequiresBidirectionalSync) score.MVVM += 2; if (requirements.DataFlow.HasMultipleDataSources) score.Hybrid += 2; // Analyze update patterns switch (requirements.UpdateFrequency) { case UpdateFrequency.Realtime: score.MVVM += 3; score.Hybrid += 2; break; case UpdateFrequency.Periodic: score.MVC += 1; score.Hybrid += 2; break; case UpdateFrequency.OnDemand: score.MVC += 3; break; } // Analyze state complexity if (requirements.StateComplexity > StateComplexity.Medium) { score.MVVM += 2; score.Hybrid += 3; } return GenerateRecommendation(score); } private ArchitectureRecommendation GenerateRecommendation(ArchitectureScore score) { var max = Math.Max(score.MVC, Math.Max(score.MVVM, score.Hybrid)); return new ArchitectureRecommendation { Primary = GetPrimaryRecommendation(score, max), Confidence = CalculateConfidence(score, max), Rationale = GenerateRationale(score), Risks = IdentifyRisks(score), AlternativeOptions = GetAlternatives(score) }; } } 

// Team Assessment Questionnaire const teamAssessment = { // Technical Skills expertise: { mvc: { level: 'expert|intermediate|beginner', yearsExperience: 5, projectsCompleted: 10 }, mvvm: { level: 'intermediate', yearsExperience: 2, projectsCompleted: 3 }, reactive: { rxjs: true, reactiveExtensions: false, signalR: true }, testing: { unitTesting: 'expert', integrationTesting: 'intermediate', e2eTesting: 'beginner' } }, // Team Preferences preferences: { debuggingStyle: 'sequential|reactive', codeOrganization: 'layered|component-based', stateManagement: 'explicit|implicit', learningAppetite: 'high|medium|low' }, // Constraints constraints: { teamSize: 5, seniorDevelopers: 2, timeToMarket: '3 months', maintenanceTeam: 'same|different', documentationNeeds: 'high|medium|low' } }; function recommendArchitecture(assessment) { const scores = { mvc: 0, mvvm: 0, hybrid: 0 }; // Weight expertise heavily if (assessment.expertise.mvc.level === 'expert') { scores.mvc += 5; } if (assessment.expertise.mvvm.level === 'expert') { scores.mvvm += 5; } // Consider learning curve vs time to market const timeConstraint = parseTimeConstraint(assessment.constraints.timeToMarket); if (timeConstraint < 6) { // months // Favor familiar architecture const maxExperience = Math.max( assessment.expertise.mvc.yearsExperience, assessment.expertise.mvvm.yearsExperience ); if (assessment.expertise.mvc.yearsExperience === maxExperience) { scores.mvc += 3; } if (assessment.expertise.mvvm.yearsExperience === maxExperience) { scores.mvvm += 3; } } // Consider maintenance if (assessment.constraints.maintenanceTeam === 'different') { // Favor simpler, more standard patterns scores.mvc += 2; scores.hybrid -= 1; } return { recommendation: getHighestScore(scores), confidence: calculateConfidence(scores), trainingNeeds: identifyTrainingGaps(assessment, getHighestScore(scores)) }; } 

// Phase 1: Identify bounded contexts for migration public class MigrationAnalyzer { public MigrationPlan CreateMigrationPlan(MvcApplication app) { var plan = new MigrationPlan(); // Identify candidates for migration var candidates = app.Controllers .Where(c => c.HasCharacteristics( highStateComplexity: true, frequentUserInteraction: true, realTimeUpdates: true )) .OrderBy(c => c.Dependencies.Count) .ToList(); // Create phased approach foreach (var controller in candidates) { var phase = new MigrationPhase { Component: controller.Name, Strategy: DetermineMigrationStrategy(controller), EstimatedEffort: EstimateEffort(controller), Dependencies: controller.Dependencies, RollbackPlan: CreateRollbackPlan(controller) }; plan.Phases.Add(phase); } return plan; } private MigrationStrategy DetermineMigrationStrategy(Controller controller) { if (controller.IsStateless) return MigrationStrategy.Strangler; if (controller.HasMinimalDependencies) return MigrationStrategy.BigBang; return MigrationStrategy.Parallel; } } // Phase 2: Implement Strangler Pattern public class StranglerMigration { // Old MVC Controller public class OrderController : Controller { [HttpGet] public async Task<IActionResult> Index() { // Check feature flag if (FeatureFlags.UseNewOrderUI) { // Redirect to new MVVM-based SPA return Redirect("/app/orders"); } // Continue with old MVC view var orders = await _orderService.GetOrdersAsync(); return View(orders); } } // New MVVM ViewModel (in separate SPA) public class OrderViewModel : ViewModelBase { // New implementation with reactive patterns public ObservableCollection<Order> Orders { get; } public ICommand RefreshCommand { get; } // Gradual migration - still uses same backend service public OrderViewModel(IOrderService orderService) { _orderService = orderService; // Same service, different presentation } } } // Phase 3: Parallel Run public class ParallelMigration { public class DualModeOrderSystem { // Both systems run simultaneously private readonly OrderController _mvcController; private readonly OrderViewModel _mvvmViewModel; private readonly IMetricsCollector _metrics; public async Task ProcessOrder(Order order) { // Process in both systems var mvcTask = ProcessWithMVC(order); var mvvmTask = ProcessWithMVVM(order); await Task.WhenAll(mvcTask, mvvmTask); // Compare results if (!ResultsMatch(mvcTask.Result, mvvmTask.Result)) { _metrics.RecordDiscrepancy(order, mvcTask.Result, mvvmTask.Result); // Use MVC result as source of truth during migration return mvcTask.Result; } _metrics.RecordSuccess(order); return mvvmTask.Result; } } } 

// Sometimes you need to migrate from MVVM to MVC (e.g., desktop to web) public class MVVMToMVCMigration { // Step 1: Extract business logic from ViewModels public class ViewModelRefactoring { // Before: Logic in ViewModel public class CustomerViewModel : ViewModelBase { public async Task SaveCustomer() { // Validation logic if (string.IsNullOrEmpty(Name)) { Errors.Add("Name is required"); return; } // Business logic if (CreditLimit > 10000 && !IsVerified) { RequireApproval = true; } // Persistence await _repository.SaveAsync(this.ToModel()); } } // After: Logic extracted to service public class CustomerService { public async Task<SaveResult> SaveCustomer(CustomerDto customer) { // Validation var validation = _validator.Validate(customer); if (!validation.IsValid) return SaveResult.Invalid(validation.Errors); // Business logic var processed = ApplyBusinessRules(customer); // Persistence await _repository.SaveAsync(processed); return SaveResult.Success(processed); } } // New MVC Controller public class CustomerController : Controller { [HttpPost] public async Task<IActionResult> Save(CustomerDto customer) { var result = await _customerService.SaveCustomer(customer); if (!result.Success) return BadRequest(result.Errors); return Ok(result.Data); } } } } 

// ❌ Anti-Pattern: Fat Controller public class BadOrderController : Controller { [HttpPost] public async Task<IActionResult> CreateOrder(OrderDto order) { // ❌ Business logic in controller if (order.Items.Sum(i => i.Price * i.Quantity) > 1000) { order.Discount = 0.1m; } // ❌ Direct database access using var connection = new SqlConnection(_connectionString); await connection.OpenAsync(); var orderId = await connection.QuerySingleAsync<int>( "INSERT INTO Orders ...", order); // ❌ Complex view logic ViewBag.DisplayMessage = order.IsUrgent ? $"Urgent order {orderId} created" : $"Order {orderId} created"; // ❌ External service calls without abstraction var emailClient = new SmtpClient(); await emailClient.SendMailAsync(...); return View(order); } } // ✅ Correct Pattern: Thin Controller public class GoodOrderController : Controller { private readonly IOrderService _orderService; private readonly INotificationService _notificationService; [HttpPost] public async Task<IActionResult> CreateOrder(OrderDto order) { // ✅ Delegate to service layer var result = await _orderService.CreateOrderAsync(order); if (!result.Success) return BadRequest(result.Errors); // ✅ Use abstracted services await _notificationService.NotifyOrderCreatedAsync(result.Order); // ✅ Simple view model mapping var viewModel = _mapper.Map<OrderViewModel>(result.Order); return View(viewModel); } } 

// ❌ Anti-Pattern: View Logic in ViewModel public class BadProductViewModel : ViewModelBase { // ❌ UI-specific logic in ViewModel public string ButtonColor => Stock > 0 ? "#00FF00" : "#FF0000"; // ❌ Direct UI control references public void ShowError(string message) { MessageBox.Show(message); // ❌ Tight coupling to UI framework } // ❌ Synchronous blocking operations public void LoadProducts() { Products = _service.GetProducts().Result; // ❌ Blocks UI thread } // ❌ Memory leaks from strong event handlers public BadProductViewModel(IProductService service) { service.ProductsChanged += OnProductsChanged; // ❌ Never unsubscribed } } // ✅ Correct Pattern: Pure ViewModel public class GoodProductViewModel : ViewModelBase, IDisposable { // ✅ Abstract UI concepts public bool IsInStock => Stock > 0; public ProductStatus Status { get; set; } // ✅ Use messaging/events for UI interaction public void ShowError(string message) { _messenger.Send(new ErrorMessage(message)); } // ✅ Async all the way public async Task LoadProductsAsync() { IsLoading = true; try { Products = await _service.GetProductsAsync(); } finally { IsLoading = false; } } // ✅ Proper cleanup private readonly IDisposable _subscription; public GoodProductViewModel(IProductService service) { // ✅ Weak events or disposable subscriptions _subscription = service.ProductsChanged .Subscribe(OnProductsChanged); } public void Dispose() { _subscription?.Dispose(); } } 

// ❌ Anti-Pattern: Mixing concerns in hybrid applications // ❌ Server and client logic mixed class BadHybridComponent extends React.Component { async componentDidMount() { // ❌ Direct database access from client component const sql = `SELECT * FROM users WHERE id = ${this.props.userId}`; const user = await database.query(sql); // This won't work! this.setState({ user }); } render() { // ❌ Server-side logic in render const hasPermission = checkServerPermissions(this.state.user); return hasPermission ? <AdminPanel /> : <AccessDenied />; } } // ✅ Correct Pattern: Clear separation class GoodHybridComponent extends React.Component { async componentDidMount() { // ✅ API call to server const response = await fetch(`/api/users/${this.props.userId}`); const user = await response.json(); this.setState({ user }); } render() { // ✅ Use data from server, don't recalculate permissions return this.state.user?.hasPermission ? <AdminPanel /> : <AccessDenied />; } } // Server-side handles data and permissions app.get('/api/users/:id', async (req, res) => { const user = await userService.getUser(req.params.id); const hasPermission = await permissionService.check(user, 'admin'); res.json({ ...user, hasPermission // Calculated server-side }); }); 

Company: Large Retailer Initial Architecture: Traditional MVC (ASP.NET MVC) Challenge: Needed real-time inventory updates and rich filtering Migration Journey: Phase 1 (Month 1-3): - Kept MVC for catalog browsing (SEO critical) - Added SignalR for inventory updates - Result: Reduced out-of-stock purchases by 40% Phase 2 (Month 4-8): - Built React components for product filtering - Server-side rendering for initial page load - Client-side takeover for interactions - Result: 60% improvement in filter interaction speed Phase 3 (Month 9-12): - Migrated checkout to SPA with Redux - Kept MVC for payment processing - Added offline capability with service workers - Result: 25% increase in conversion rate Lessons Learned: - Don't migrate everything at once - Keep SEO-critical paths in MVC - Use hybrid approach for best of both worlds - Measure performance at each phase Final Architecture: - MVC: Product pages, SEO landing pages - React + Redux: Checkout, user account - SignalR: Real-time inventory - Service Workers: Offline browsing 

Company: Investment Bank Initial Architecture: WPF with MVVM Challenge: Needed web access for remote traders Migration Journey: Phase 1: Analysis - 300+ ViewModels with complex bindings - Real-time data from 15 sources - 50ms latency requirement Phase 2: Hybrid Approach - Built ASP.NET Core API layer - Kept WPF for trading floor (performance critical) - Built Blazor WebAssembly for remote access - Shared ViewModels via .NET Standard library Phase 3: Optimization - Implemented WebSocket feeds - Added Redis for caching - Used gRPC for inter-service communication Results: - Desktop: 10ms latency (exceeded requirement) - Web: 45ms latency (met requirement) - Code reuse: 70% of business logic shared - Maintenance: Single team maintains both Architecture Decision: - Kept MVVM for both platforms - Blazor allowed ViewModel reuse - SignalR provided real-time updates - Hybrid approach met all requirements 

Company: SaaS Startup Initial: React SPA with Redux Problem: Poor SEO, slow initial load Pivot Strategy: Week 1-2: Analysis - 80% of traffic from search - 3.5 second initial load time - 45% bounce rate Week 3-4: Next.js Migration - Server-side rendering for public pages - Keep SPA for authenticated app - Incremental static regeneration Week 5-6: Optimization - Code splitting - Image optimization - CDN deployment Results: - Initial load: 3.5s → 0.8s - SEO: 300% increase in organic traffic - Bounce rate: 45% → 22% - Development velocity: Maintained Learning: - Framework choice matters less than right tool for job - Hybrid SSR/SPA optimal for many scenarios - Performance metrics should drive architecture 

## Architecture Decision Checklist ### ✅ MVC Checklist - [ ] Primary interaction is request/response - [ ] SEO is critical for success - [ ] Server-side processing is required - [ ] Team has MVC expertise - [ ] Stateless operations predominate - [ ] Clear transaction boundaries needed - [ ] Horizontal scaling required - [ ] Simple CRUD operations - [ ] Progressive enhancement important - [ ] Limited client-side state ### ✅ MVVM Checklist - [ ] Rich, interactive UI required - [ ] Complex client-side state - [ ] Real-time updates needed - [ ] Offline capability important - [ ] Multiple views of same data - [ ] Desktop or mobile app - [ ] Data binding would simplify code - [ ] Two-way synchronization needed - [ ] Team comfortable with reactive patterns - [ ] Long-lived client sessions ### ✅ Hybrid Checklist - [ ] Need both SSR and client interactivity - [ ] SEO + rich interactions - [ ] Gradual migration planned - [ ] Different requirements for different parts - [ ] Team has diverse skills - [ ] Modern framework ecosystem desired - [ ] Real-time + traditional operations - [ ] Progressive web app requirements - [ ] API-first architecture - [ ] Microservices architecture ### 🚫 Red Flags for MVC - [ ] Extensive real-time requirements - [ ] Complex state synchronization - [ ] Rich animations/interactions - [ ] Offline-first requirement - [ ] Native mobile app needed ### 🚫 Red Flags for MVVM - [ ] SEO is critical - [ ] Simple CRUD application - [ ] Team lacks reactive experience - [ ] Tight deadline with no learning time - [ ] Server-side processing heavy ### 🚫 Red Flags for Hybrid - [ ] Small team without diverse skills - [ ] Simple requirements - [ ] Tight budget - [ ] Need to minimize complexity - [ ] Single platform target