How to create REST APIs in ASP.NET Core? Follow :

Short answer: Creating REST APIs in ASP.NET Core is straightforward using controllers or minimal APIs.

Explain a bit more

Traditional Controller-Based API dotnet new webapi -n MyApi Program.cs: var builder = WebApplication.CreateBuilder(args); builder.Services.AddControllers(); var app = builder.Build(); app.MapControllers(); app.Run(); Controller: [ApiController] [Route("api/[controller]")] public class ProductsController : ControllerBase [HttpGet] public IActionResult GetAll() => Ok(new[] { "Laptop", "Phone" }); ✅ You get RESTful endpoints automatically (GET /api/products). Creating REST APIs in ASP.NET Core is straightforward using controllers or minimal APIs.

Example code

Traditional Controller-Based API dotnet new webapi -n MyApi Program.cs: var builder = WebApplication.CreateBuilder(args); builder.Services.AddControllers(); var app = builder.Build(); app.MapControllers(); app.Run(); Controller: [ApiController] [Route("api/[controller]")] public class ProductsController : ControllerBase [HttpGet] public IActionResult GetAll() => Ok(new[] { "Laptop", "Phone" }); ✅ You get RESTful endpoints automatically (GET /api/products). Creating REST APIs in ASP.NET Core is straightforward using controllers or minimal APIs. Example: Traditional Controller-Based API dotnet new webapi -n MyApi Program.cs: var builder = WebApplication.CreateBuilder(args); builder.Services.AddControllers(); var app = builder.Build(); app.MapControllers(); app.Run(); Controller: [ApiController] [Route("api/[controller]")] public class ProductsController : ControllerBase [HttpGet] public IActionResult GetAll() => Ok(new[] { "Laptop", "Phone" }); ✅ You get RESTful endpoints automatically (GET /api/products). Creating REST APIs in ASP.NET Core is straightforward using controllers or minimal APIs. Example: Traditional Controller-Based API dotnet new webapi -n MyApi Program.cs: var builder = WebApplication.CreateBuilder(args); builder.Services.AddControllers(); var app = builder.Build(); app.MapControllers(); app.Run(); Controller: [ApiController] [Route("api/[controller]")] public class ProductsController : ControllerBase [HttpGet] public IActionResult GetAll() => Ok(new[] { "Laptop", "Phone" }); ✅ You get RESTful endpoints automatically (GET /api/products). 🧱 2. What is the [ApiController] attribute? [ApiController] simplifies building APIs by adding smart defaults: Automatic model validation → 400 Bad Request on invalid models Automatic [FromBody], [FromQuery], etc. inference Follow : ProblemDetails JSON response for errors Example: [ApiController] [Route("api/[controller]")] public class OrdersController : ControllerBase [HttpPost] public IActionResult CreateOrder(Order order) if (!ModelState.IsValid) return BadRequest(ModelState); return CreatedAtAction(nameof(CreateOrder), new { id = 1 }, order); 📦 3. How does content negotiation work? Content negotiation allows clients to request responses in a specific format (JSON, XML, etc.) using the Accept header. ASP.NET Core automatically picks the best formatter: GET /api/products Accept: application/json Response → JSON GET /api/products Accept: application/xml Response → XML (if XML formatter is added) Follow : Enable XML Support: builder.Services.AddControllers() .AddXmlSerializerFormatters(); 🧭 4. How to handle versioning in APIs? You can version APIs to maintain backward compatibility using the Microsoft.AspNetCore.Mvc.Versioning package. Install: dotnet add package Microsoft.AspNetCore.Mvc.Versioning Configure: builder.Services.AddApiVersioning(options => options.DefaultApiVersion = new ApiVersion(1, 0); options.AssumeDefaultVersionWhenUnspecified = true; options.ReportApiVersions = true; }); Use in controllers: [ApiVersion("1.0")] [Route("api/v{version:apiVersion}/products")] [ApiController] public class ProductsV1Controller : ControllerBase [HttpGet] public IActionResult Get() => Ok("Version 1"); ⚠ 5. What is ProblemDetails? Follow : ProblemDetails is a standardized JSON structure for API error responses (RFC 7807). Example Output: "type": " "title": "Resource not found", "status": 404, "detail": "Product with ID 5 was not found" Usage: return NotFound(new ProblemDetails Title = "Product not found", Status = StatusCodes.Status404NotFound, Detail = "The product ID 5 does not exist." }); 🚦 6. How to return custom HTTP status codes? You can use built-in helpers from ControllerBase: Method Status Code Ok() 200 Created() / CreatedAtAction() 201 NoContent() 204 BadRequest() 400 Unauthorized() 401 Follow : NotFound() 404 StatusCode(500) Custom Example: return StatusCode(503, "Service temporarily unavailable"); 📄 7. How to implement pagination in APIs? Pagination helps manage large datasets efficiently. Example: [HttpGet] public IActionResult GetProducts([FromQuery] int page = 1, [FromQuery] int size = 10) var data = _context.Products .Skip((page - 1) * size) .Take(size) .ToList(); var totalCount = _context.Products.Count(); Response.Headers.Add("X-Total-Count", totalCount.ToString()); return Ok(data); ✅ Supports GET /api/products?page=2&size=5. 🔐 8. How to secure APIs with JWT tokens? Use JWT (JSON Web Token) authentication for stateless security. Follow : Setup in Program.cs: builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationS cheme) .AddJwtBearer(options => options.TokenValidationParameters = new TokenValidationParameters ValidateIssuer = true, ValidIssuer = " ValidateAudience = true, ValidAudience = " IssuerSigningKey = new SymmetricSecurityKey( Encoding.UTF8.GetBytes("super-secret-key")) }); Then protect controllers: [Authorize] [ApiController] [Route("api/[controller]")] public class OrdersController : ControllerBase [HttpGet] public IActionResult GetOrders() => Ok("Secure data"); ⚡ 9. What is rate limiting in .NET 8? .NET 8 introduces built-in rate limiting middleware to control API request rates. Example: builder.Services.AddRateLimiter(options => Follow : options.AddFixedWindowLimiter("fixed", opt => opt.PermitLimit = 5; // 5 requests opt.Window = TimeSpan.FromSeconds(10); // per 10 seconds opt.QueueLimit = 0; }); }); var app = builder.Build(); app.UseRateLimiter(); app.MapGet("/api/data", () => "Hello") .RequireRateLimiting("fixed"); ✅ Prevents abuse or DDoS attacks by throttling requests. 🚨 10. How do you handle exceptions in APIs? Use global exception handling middleware instead of try/catch everywhere. Example: app.UseExceptionHandler("/error"); app.Map("/error", (HttpContext context) => var exception = context.Features.Get<IExceptionHandlerFeature>()?.Error; return Results.Problem(title: "Unexpected error", detail: exception?.Message); }); Or write a custom middleware for consistent error formatting. Follow : 🧾 11. How to use Swagger / OpenAPI? Swagger generates interactive API documentation automatically. Setup: builder.Services.AddEndpointsApiExplorer(); builder.Services.AddSwaggerGen(); var app = builder.Build(); if (app.Environment.IsDevelopment()) app.UseSwagger(); app.UseSwaggerUI(); Run → Navigate to ✅ You can test endpoints directly from the browser. 🧰 12. What is NSwag or Swashbuckle? Both tools generate OpenAPI/Swagger documentation, but with slight differences: Tool Description Swashbuckle.AspNetCor Most common; adds Swagger UI, docs, and JSON schema NSwag Adds extra features like client SDK generation for C#/TypeScript Example (NSwag client generation): Follow : nswag openapi2csclient /input: /output:Client.cs 📤 13. How to upload files via Web API? Use IFormFile for file uploads. Controller Example: [HttpPost("upload")] public async Task<IActionResult> UploadFile(IFormFile file) if (file == null || file.Length == 0) return BadRequest("No file uploaded."); var path = Path.Combine("wwwroot/uploads", file.FileName); using var stream = new FileStream(path, FileMode.Create); await file.CopyToAsync(stream); return Ok(new { file.FileName, file.Length }); Client sends multipart/form-data POST requests. 🌐 14. How to implement CORS? CORS (Cross-Origin Resource Sharing) allows requests from other domains (e.g., frontend apps). Enable in Program.cs: builder.Services.AddCors(options => Follow : options.AddPolicy("AllowReactApp", policy => policy.WithOrigins(" .AllowAnyHeader() .AllowAnyMethod()); }); var app = builder.Build(); app.UseCors("AllowReactApp"); ✅ Now your React or Angular frontend can call your API safely. 🚀 15. What’s new in .NET 8 Minimal APIs? Minimal APIs let you build lightweight REST endpoints without controllers — great for microservices. Example: var builder = WebApplication.CreateBuilder(args); var app = builder.Build(); app.MapGet("/products", () => new[] { "Phone", "Tablet" }); app.MapPost("/products", (Product product) => Results.Created($"/products/{product.Id}", product)); app.Run(); New in .NET 8: Route groups for grouping endpoints Input validation with [Validate] attributes Enhanced OpenAPI (Swagger) support Rate limiting, Authorization, and Filters integration Follow : Typed results for consistent HTTP responses ✅ Minimal APIs now rival traditional controllers for small, fast APIs. Performance & Caching

Real-world example (ShopNest)

ShopNest admin screens use MVC: controller loads data, Razor view renders HTML, Tag Helpers build forms safely.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.