public class ProductController : Controller
{
    // When user requests /Product/Details/5
    public ActionResult Details(int id)
    {
        // 1. Process request - retrieve data
        Product product = GetProductFromDatabase(id);

        // 2. Return ViewResult with model
        return View(product); // View engine renders Product details view
    }

    private Product GetProductFromDatabase(int id)
    {
        // Database query logic
        return new Product { Id = id, Name = "Sample Product" };
    }
}

public class StudentController : Controller
{
    public ActionResult Index()
    {
        // Using ViewBag (dynamic)
        ViewBag.Title = "Student List";

        // Using ViewData (dictionary)
        ViewData["Count"] = 10;

        // Using TempData (survives redirect)
        TempData["SuccessMessage"] = "Student created successfully";

        return View();
    }

    // In View
    // @ViewBag.Title          // Dynamic access
    // @ViewData["Count"]       // Dictionary access
    // @TempData["SuccessMessage"] // Survives redirect
}

public interface IEmailService
{
    void SendEmail(string to, string subject, string body);
}

public class EmailService : IEmailService
{
    public void SendEmail(string to, string subject, string body)
    {
        // Email sending logic
    }
}

// In Startup.cs ConfigureServices
public void ConfigureServices(IServiceCollection services)
{
    services.AddScoped<IEmailService, EmailService>();
}

// In Controller - DI injects EmailService
public class UserController : Controller
{
    private readonly IEmailService _emailService;

    public UserController(IEmailService emailService)
    {
        _emailService = emailService;
    }

    public ActionResult Register(User user)
    {
        _emailService.SendEmail(user.Email, "Welcome", "...");
        return View();
    }
}

// appsettings.json
{
  "ConnectionStrings": {
    "DefaultConnection": "Server=localhost;Database=MyDb;Trusted_Connection=true;"
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information"
    }
  }
}

// Reading configuration
public class HomeController : Controller
{
    private readonly IConfiguration _configuration;

    public HomeController(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public ActionResult Index()
    {
        string connString = _configuration["ConnectionStrings:DefaultConnection"];
        return View();
    }
}

// In Startup.cs ConfigureServices
public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthorization(options =>
    {
        options.AddPolicy("CanEdit", policy =>
            policy.RequireClaim("EditPermission", "true"));
    });
}

// Using [Authorize] with policy
public class ArticleController : Controller
{
    [Authorize(Policy = "CanEdit")]
    public ActionResult Edit(int id)
    {
        return View();
    }

    [Authorize(Roles = "Admin")]
    public ActionResult Delete(int id)
    {
        return View();
    }
}

// Model - Domain model
public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
}

// ViewModel - Tailored for view
public class ProductViewModel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string FormattedPrice { get; set; }
    public bool IsAvailable { get; set; }
}

// Controller maps Model to ViewModel
public ActionResult Details(int id)
{
    Product product = _repository.GetProduct(id);

    var viewModel = new ProductViewModel
    {
        Id = product.Id,
        Name = product.Name,
        FormattedPrice = product.Price.ToString("C"),
        IsAvailable = product.Stock > 0
    };

    return View(viewModel);
}

public class ProductController : Controller
{
    private readonly ILogger<ProductController> _logger;

    public ProductController(ILogger<ProductController> logger)
    {
        _logger = logger;
    }

    public ActionResult Index()
    {
        _logger.LogInformation("Listing products");

        try
        {
            var products = GetProducts();
            return View(products);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error retrieving products");
            throw;
        }
    }
}

// Dockerfile for containerized deployment
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /app
COPY . .
RUN dotnet restore
RUN dotnet publish -c Release -o out

FROM mcr.microsoft.com/dotnet/runtime:6.0
WORKDIR /app
COPY --from=build /app/out .
EXPOSE 80
ENTRYPOINT ["dotnet", "MyApp.dll"]