What ASP.NET Core API Features Should Freshers Practice Before a Developer Interview?

A fresher preparing for an ASP.NET Core developer interview should go beyond memorising `GET`, `POST`, `PUT` and `DELETE`. Interviewers often want to see whether the candidate understands how a request moves through an API and how a maintainable API should be structured. A useful learning architecture is: ```text Client | v HTTP Request | v ASP.NET Core Middleware | v Authentication / Authorisation | v API Endpoint | v Application / Service Layer | v Data Access | v Database ``` Start by becoming comfortable building CRUD APIs. You should be able to create endpoints, understand routing, accept request data, validate it, call application logic and return appropriate HTTP responses. Then practise these areas deeply: **Routing and HTTP semantics** Know the purpose of GET, POST, PUT, PATCH and DELETE rather than treating them as method names. Understand route parameters, query strings, request bodies and status codes such as `200`, `201`, `204`, `400`, `401`, `403`, `404` and `500`. **Dependency Injection** ASP.NET Core has built-in dependency injection. A candidate should understand why a controller or service should receive dependencies rather than instantiate infrastructure classes everywhere. For example: ```csharp public class OrdersController : ControllerBase { private readonly IOrderService _orderService; public OrdersController(IOrderService orderService) { _orderService = orderService; } } ``` The important interview question is not simply "What is DI?" It is: **Why does dependency injection improve testability and maintainability?** **Request models and validation** Avoid accepting arbitrary database entities as API contracts without considering the design implications. Practise request/response DTOs and validation. **Authentication and authorisation** Be able to explain the difference: ```text Authentication "Who are you?" ↓ Authorisation "What are you allowed to do?" ``` ASP.NET Core treats authentication and authorisation as separate concerns, with authentication establishing identity and authorisation deciding access to resources. **Middleware** Understand that middleware forms an HTTP processing pipeline. ```text Request ↓ Exception Handling ↓ HTTPS ↓ Authentication ↓ Authorisation ↓ Endpoint ↓ Response ``` Candidates should understand that middleware order can affect application behaviour. **Exception handling** Do not write an API where every endpoint contains large `try/catch` blocks. Learn centralised exception handling and how application exceptions should become meaningful HTTP responses. **Async programming** Practise `async` and `await`, particularly around I/O operations such as database and external API calls. **Logging** Understand structured application logging and why production APIs require enough context to troubleshoot failures without exposing sensitive information. **OpenAPI documentation** Be comfortable exposing and testing documented API operations using the OpenAPI ecosystem rather than treating API documentation as an afterthought. **CORS** Freshers frequently memorise the word CORS without understanding it. Browser same-origin policy restricts cross-origin requests, and ASP.NET Core provides CORS configuration for explicitly allowed scenarios. A strong practice project would therefore be: ```text Order Management API Customers | +--- Orders | +--- Products | +--- Authentication | +--- Validation | +--- Logging | +--- Exception Handling | +--- Database ``` Build it rather than only watching tutorials. During interviews, a candidate who can explain **why an API was designed in a particular way** will usually demonstrate much stronger understanding than someone who only remembers syntax. **Discussion:** Which ASP.NET Core topic causes the most difficulty during interviews—dependency injection, authentication, middleware, Entity Framework Core, or exception handling?