Dotnet Migration Patterns

Configuration Migration

web.config → appsettings.json

<!-- Before: web.config -->
<appSettings>
  <add key="ApiUrl" value="https://api.example.com" />
  <add key="MaxRetries" value="3" />
</appSettings>
<connectionStrings>
  <add name="DefaultConnection"
       connectionString="Server=.;Database=MyDb;Trusted_Connection=True;"
       providerName="System.Data.SqlClient" />
</connectionStrings>

// After: appsettings.json
{
  "ApiUrl": "https://api.example.com",
  "MaxRetries": 3,
  "ConnectionStrings": {
    "DefaultConnection": "Server=.;Database=MyDb;Trusted_Connection=True;"
  }
}

Configuration Access

// Before
var value = ConfigurationManager.AppSettings["ApiUrl"];
var conn = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

// After
var value = configuration["ApiUrl"];
var conn = configuration.GetConnectionString("DefaultConnection");
// Or with strongly-typed options:
services.Configure<MyOptions>(configuration.GetSection("MyOptions"));

WCF to REST Migration

Service Contract → Controller

// Before: WCF
[ServiceContract]
public interface IOrderService
{
    [OperationContract]
    Order GetOrder(int orderId);

    [OperationContract]
    void CreateOrder(Order order);
}

// After: ASP.NET Core Web API
[ApiController]
[Route("api/[controller]")]
public class OrdersController : ControllerBase
{
    [HttpGet("{orderId}")]
    public async Task<ActionResult<Order>> GetOrder(int orderId) { }

    [HttpPost]
    public async Task<ActionResult<Order>> CreateOrder(Order order) { }
}

Authentication Migration

Windows/Forms Auth → Entra ID

// Before: Forms Authentication
FormsAuthentication.SetAuthCookie(username, false);

// After: Microsoft Identity Web
services.AddMicrosoftIdentityWebAppAuthentication(configuration);
// Or for APIs:
services.AddMicrosoftIdentityWebApiAuthentication(configuration);

Data Access Migration

ADO.NET → Entity Framework Core

// Before: ADO.NET
using (var conn = new SqlConnection(connStr))
{
    var cmd = new SqlCommand("SELECT * FROM Orders WHERE Id = @id", conn);
    cmd.Parameters.AddWithValue("@id", orderId);
    conn.Open();
    var reader = cmd.ExecuteReader();
}

// After: EF Core
var order = await context.Orders.FindAsync(orderId);

Calling Stored Procedures from EF Core

// When keeping SPs:
var results = await context.Orders
    .FromSqlInterpolated($"EXEC dbo.sp_GetOrdersByCustomer {customerId}")
    .ToListAsync();

Dependency Injection

// Before: Manual instantiation or Service Locator
var service = new OrderService(new OrderRepository());

// After: Built-in DI
services.AddScoped<IOrderService, OrderService>();
services.AddScoped<IOrderRepository, OrderRepository>();

Key NuGet Package Replacements