.NET Core Interview Questions Lecture

Introduction

• 30 important questions for .NET Core interviews
• Subscribe to the channel for more content

Basic Concepts

What is .NET Core?

• New framework, open-source, developed by Microsoft
• Different from .NET Framework and Mono for Xamarin
• Shares common standard libraries (".NET Standard Library")

Advantages of .NET Core

1. Cross-Platform: Runs on Windows, Linux, and Mac (unlike .NET Framework which runs only on Windows)
2. Open Source: Free to use, modifiable, distributable
3. Modern UI Integration: Easier integration with Angular, React
4. Hosting: Can be hosted on multiple servers like Kestrel, Nginx
5. Built-In Dependency Injection: Enables loosely coupled design
6. Multiple IDE Support: Visual Studio, Visual Studio for Mac, Visual Studio Code

Project Structure in ASP.NET Core

Default Files and Directories

1. wwwroot: Stores static files (JS, CSS, images)
2. program.cs: Entry point of the application
3. startup.cs: Configures services and request pipeline
4. appsettings.json: Configuration settings (e.g., database connection strings)

Role of Files

program.cs

• Entry point via Main() method
• Builds the host server
• Calls startup class via CreateHostBuilder method and Lambda expression

startup.cs

• Configures services and request pipeline
• Includes ConfigureServices and Configure methods

ConfigureServices and Configure Methods

ConfigureServices

• Defines and adds services (e.g., AddControllersWithViews)
• Optional based on request types

Configure

• Configures the request pipeline
• Mandatory methods in order
• Middleware components (UseRouting, UseAuthorization, etc.)

Dependency Injection

Introduction

• Creates loosely coupled design
• Avoids tight coupling by using interfaces and dependency injection

Implementation

1. Interface Creation: IStudent interface with method declaration
2. Class Implementation: MathStudent and ScienceStudent implementing IStudent
3. Service Registration: In startup.cs (AddSingleton<IStudent, MathStudent>())
4. Controller Adjustment: Inject IStudent in controllers via constructor
5. Switching Implementation: Change service registration in startup.cs to switch between MathStudent and ScienceStudent

Service Lifetimes

1. Singleton: Single instance shared across application
2. Scoped: Single instance shared per request
3. Transient: New instance per request

Middleware in ASP.NET Core

What is Middleware?

• Component executed on every request
• Defined in Configure method as middleware components
• Use: Adds to request pipeline, allows next middleware
• Run: Terminates middleware execution
• Map: Conditional middleware execution based on URL

Kestrel Web Server

• Lightweight web server for ASP.NET Core
• Supports cross-platform deployment

In-Process vs. Out-of-Process Hosting

• In-Process: Uses IIS
• Out-Of-Process: Supports Kestrel, IIS as reverse proxy

Hosting Configuration

• Set ASPNETCORE_HOSTINGMODEL to InProcess or OutOfProcess
• CreateHostBuilder builds and adds host

Configuration Settings

Techniques

1. appsettings.json: Default technique
2. Azure Key Vault: Used in Azure hosting
3. Environment Variables
4. In-Memory .NET Objects
5. Command Line Arguments
6. Custom Providers

Routing in ASP.NET Core

Conventional Routing

• Handles HTTP requests based on URL pattern (Controller/Action/Parameter)
• Defined in UseEndpoints method

Attribute Routing

• Uses attributes to manipulate URL behavior
• Route attribute to map URL to controller action

Request Processing Pipeline

• Flow: HTTP request -> Middleware -> Routing -> Controller initialization -> Action method -> View result -> HTTP response

.NET Standard

• A set of APIs implemented by platforms to ensure compliance

Razor Pages

• Page-centric development model
• Similar to ASP.NET WebForms

Dependency Injection in Views

• Use @inject directive in views for injecting services

Custom Middleware

• Create custom middleware class
• Add custom logic in Invoke method
• Register custom middleware in Configure method

State Management Techniques

1. Cookies: Store data in the user’s browser
2. Session State: Transfer data between pages using cookies
3. TempData: Transfer data from controller to view
4. Query String: Append data to URL
5. Hidden Fields: Process data within the same page during postbacks

Model Validation

• Uses data annotations to enforce rules (e.g., Required attribute)
• Define rules in model classes

Error Handling

• Set error handling in Configure method
• Different handling for development and production environment

Enabling Sessions

• Service and middleware provided by Microsoft.AspNetCore.Session
• Register AddSession in ConfigureServices
• Use app.UseSession in Configure

Model Binding

• Maps HTTP request data to controller action method parameters
• Automatically converts data types (e.g., strings to integers)