.NET Full Stack Interview Questions and Answers

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1. What is the difference between .NET Framework, .NET Core, and .NET 5+?

   • Answer:

     • .NET Framework: Windows-only, older version of .NET.

     • .NET Core: Cross-platform, open-source, modular, and faster than .NET Framework.

     • .NET 5+: Unified version of .NET Core and .NET Framework, supporting Windows, Linux, and macOS.

2. What are the benefits of using .NET Core over .NET Framework?

   • Answer:

     • Cross-platform support

     • High performance and lightweight

     • Built-in dependency injection

     • Modular and supports microservices architecture

3. What is Kestrel in ASP.NET Core?

   • Answer: Kestrel is a cross-platform, lightweight web server used by default in ASP.NET Core applications for handling HTTP requests.

4. What is the difference between a class and an interface in C#?

   • Answer:

     • A class can have implementations (methods and properties) and can be instantiated.

     • An interface only defines method signatures and properties but does not provide implementations.

5. What is a Singleton design pattern in C#?

   • Answer: A Singleton ensures that only one instance of a class exists and provides a global access point. It is commonly used for logging, caching, and database connections.

6. What is Middleware in ASP.NET Core?

   • Answer: Middleware is a component that processes HTTP requests in the ASP.NET Core request pipeline. Examples include authentication, logging, and error handling.

7. How do you implement authentication in ASP.NET Core?

   • Answer: Authentication can be implemented using JWT (JSON Web Tokens), OAuth, or Identity Server. ASP.NET Core Identity provides built-in authentication support.

8. What are the different return types in ASP.NET Core controllers?

   • Answer:

     • IActionResult (for different types of responses)

     • JsonResult (returns JSON data)

     • ViewResult (returns a View)

     • FileResult (returns a file)

9. What is Lazy Loading in Entity Framework?

   • Answer: Lazy Loading is a technique where related data is only loaded when accessed for the first time, improving initial query performance.

10. What is Eager Loading in Entity Framework?

• Answer: Eager Loading loads related data at the time of the initial query using the .Include() method, reducing multiple database queries

Sure! Here's a basic text format with .NET Full Stack Interview Questions and Answers, questions 11 to 25, suitable for beginners:

11. What is the difference between ref and out in C#?

• ref requires that the variable be initialized before it is passed.

• out does not require the variable to be initialized before being passed. It must be assigned inside the method.

12. What is the difference between value types and reference types in C#?

• Value types store data directly (e.g., int, bool).

• Reference types store references to the data (e.g., class, string).

13. What is MVC in ASP.NET?

• MVC stands for Model-View-Controller.

  • Model handles data and business logic.

  • View displays the data (UI).

  • Controller handles user input and updates Model and View.

14. What is Entity Framework (EF)?

• EF is an ORM (Object-Relational Mapper) that helps developers work with databases using .NET objects, without writing much SQL code.

15. What is the difference between IEnumerable and IQueryable?

• IEnumerable executes queries in-memory and is best for LINQ to Objects.

• IQueryable executes queries on the database server and is best for LINQ to Entities.

16. What are partial views in ASP.NET MVC?

• Partial views are reusable view components used to render parts of a web page, like a widget or a form.

17. What is the purpose of the using statement in C#?

• It ensures that resources (like file streams or database connections) are disposed of properly after use.

18. What is middleware in ASP.NET Core?

• Middleware are components in the request pipeline that handle requests and responses. Examples: authentication, logging, routing.

19. What is dependency injection (DI)?

• DI is a design pattern used to achieve loose coupling. Objects receive their dependencies from an external source rather than creating them.

20. What is the difference between an abstract class and an interface in C#?

• Abstract class can have implementations and fields.

• Interface only defines members, no implementation (before C# 8.0).

21. What is Razor in ASP.NET?

• Razor is a syntax used in ASP.NET for embedding server-based code (C#) into HTML pages.

22. What is ViewBag and ViewData in MVC?

• Both are used to pass data from controller to view.

  • ViewBag is dynamic.

  • ViewData is a dictionary of objects (key-value).

23. How do you connect to a SQL Server database in .NET?

• Using SqlConnection, SqlCommand, etc., from System.Data.SqlClient.

• Or by using Entity Framework for higher abstraction.

24. What are the access modifiers in C#?

• public, private, protected, internal, protected internal, and private protected.

25. What is the difference between synchronous and asynchronous methods in .NET?

• Synchronous methods block the thread until the task completes.

• Asynchronous methods (async/await) allow other tasks to run while waiting for the result.

Let me know if you'd like these in a downloadable format or continued from 26 onward!

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1. What is the difference between .NET 5, .NET 6, and .NET 7?

   • Answer: .NET 5 was the first unified version after .NET Core, with performance improvements. .NET 6 introduced LTS (Long-Term Support) and improved Blazor, while .NET 7 focused on cloud-native optimizations and performance enhancements.

2. How do you implement CQRS in .NET Core?

   • Answer: CQRS (Command Query Responsibility Segregation) is implemented by separating read (queries) and write (commands) operations using MediatR and different databases for each operation if needed.

3. What is the use of MediatR in .NET Core?

   • Answer: MediatR is a library that implements the Mediator pattern to decouple handlers from controllers, making the architecture more scalable and maintainable.

4. How does gRPC work in .NET Core?

   • Answer: gRPC is a high-performance RPC framework that uses Protobuf for serialization and HTTP/2 for communication, making it efficient for microservices.

5. What is the difference between Microservices and Serverless in .NET?

   • Answer:

     • Microservices: Independent services deployed and managed separately.

     • Serverless: Code runs in response to events without server management (e.g., Azure Functions).

6. Explain the use of Minimal APIs in .NET Core.

   • Answer: Minimal APIs provide a lightweight way to create APIs using fewer files and configurations, reducing boilerplate code.

7. How do you implement multi-threading in .NET Core?

   • Answer: Using Task.Run(), Parallel.ForEach(), async/await, or ThreadPool to perform parallel execution.

8. What is the difference between Redis Cache and Memory Cache in .NET Core?

   • Answer:

     • Memory Cache: Stores data in RAM, suitable for single-instance applications.

     • Redis Cache: A distributed caching solution used for scaling across multiple instances.

9. How does DDD (Domain-Driven Design) apply to .NET applications?

   • Answer: DDD structures applications based on business logic with concepts like Entities, Value Objects, Aggregates, and Domain Events.

10. How do you optimize an ASP.NET Core application for high performance?

    • Answer:

      • Enable Response Compression

      • Use Asynchronous Programming

      • Optimize Database Queries

      • Enable Caching

      • Use Load Balancing

11. What is Ocelot and how is it used in .NET?

    • Answer: Ocelot is an API Gateway library for managing microservices, handling routing, authentication, logging, and request aggregation.

12. How does .NET Core support API Rate Limiting?

    • Answer: By using middleware or third-party libraries like AspNetCoreRateLimit to control the number of requests per user.

13. How do you implement Circuit Breaker in .NET Core?

    • Answer: Using Polly, a resilience library that prevents repeated failures by stopping requests when a service is down.

14. How does Entity Framework Core handle migrations in a CI/CD pipeline?

    • Answer: Migrations can be automated using dotnet ef migrations script to generate SQL scripts and apply them during deployment.

15. What is the difference between API Versioning and API Gateway?

    • Answer:

      • API Versioning: Managing multiple versions of an API to support backward compatibility.

      • API Gateway: A single entry point that manages multiple APIs, including authentication, logging, and load balancing.

16. What are the different types of Azure App Services in .NET?

    • Answer:

      • Web Apps

      • API Apps

      • Mobile Apps

      • Functions (Serverless)

17. What is the difference between Docker and Kubernetes in .NET applications?

    • Answer:

      • Docker: A containerization tool for packaging applications.

      • Kubernetes: A container orchestration system that manages scaling and networking.

18. How do you secure a .NET Core Web API using OAuth2.0?

    • Answer: By integrating IdentityServer4 or Azure AD and configuring JWT authentication.

19. How do you implement GraphQL in .NET Core?

    • Answer: Using HotChocolate or GraphQL.NET to define queries and mutations instead of REST APIs.

20. What is the difference between RabbitMQ and Kafka in .NET applications?

    • Answer:

      • RabbitMQ: Message broker optimized for low-latency communication.

      • Kafka: Distributed event streaming platform suited for real-time analytics.

21. How do you integrate Elasticsearch with a .NET Core application?

    • Answer: Using the NEST client to perform full-text search, aggregations, and analytics on data.

22. What is Clean Architecture and how does it benefit .NET Core applications?

    • Answer: Clean Architecture separates concerns into layers (Domain, Application, Infrastructure, Presentation) to improve maintainability and scalability.

23. How do you handle distributed transactions in .NET Core Microservices?

    • Answer: Using the Saga Pattern, orchestrators, or Outbox Pattern with message queues.

24. What is the difference between gRPC and REST APIs?

    • Answer:

      • gRPC: Uses Protobuf, HTTP/2, and is faster but complex.

      • REST: Uses JSON over HTTP/1.1, simpler and widely used.

25. How do you implement Background Jobs in .NET Core?

    • Answer: Using Hangfire, Quartz.NET, or Azure Functions for scheduled tasks.

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1. What is the difference between .NET Core and .NET Framework?

   • Answer: .NET Core is cross-platform, open-source, and optimized for cloud applications, while .NET Framework is Windows-only and suited for enterprise applications.

2. Explain the MVC architecture in .NET.

   • Answer: The Model-View-Controller (MVC) architecture separates concerns: Model handles data, View handles UI, and Controller manages business logic.

3. What is Dependency Injection in .NET Core?

   • Answer: Dependency Injection (DI) is a design pattern that promotes loose coupling by injecting dependencies via constructors or methods.

4. How does Entity Framework Core differ from Entity Framework?

   • Answer: EF Core is lightweight, cross-platform, and does not support all EF6 features but provides better performance and flexibility.

5. What is Middleware in .NET Core?

   • Answer: Middleware is software that processes requests and responses in a pipeline, such as authentication, logging, and exception handling.

6. How do you implement authentication in .NET Core Web API?

   • Answer: By using JWT (JSON Web Token), OAuth2, or IdentityServer4 for secure user authentication.

7. What is the difference between a ViewComponent and a Partial View in ASP.NET Core?

   • Answer: A ViewComponent is more powerful as it supports logic execution, whereas a Partial View is just reusable HTML.

8. What is the purpose of the IHostedService interface in .NET Core?

   • Answer: It is used to create background services, such as scheduled tasks or long-running processes.

9. Explain the difference between Asynchronous and Synchronous programming in .NET.

   • Answer: Asynchronous programming (async/await) allows non-blocking execution, whereas synchronous execution blocks the thread until completion.

10. How do you implement logging in .NET Core?

    • Answer: Using built-in ILogger interface or third-party libraries like Serilog, NLog, and Log4Net.

11. What is the difference between Transient, Scoped, and Singleton services in .NET Core DI?

    • Answer:

      • Transient: New instance created per request.

      • Scoped: Instance shared per request scope.

      • Singleton: One instance shared across the application.

12. What is the difference between SQL Server and NoSQL databases like MongoDB?

    • Answer: SQL Server is a relational database using structured schemas, while MongoDB is NoSQL, using flexible JSON-like documents.

13. How do you improve the performance of an ASP.NET Core application?

    • Answer: By using caching, response compression, optimizing queries, and enabling asynchronous operations.

14. What is the role of Docker in .NET Core?

    • Answer: Docker containerizes applications, making them portable, scalable, and easier to deploy.

15. What is the difference between REST and GraphQL?

    • Answer: REST exposes fixed endpoints, while GraphQL allows flexible data queries with a single endpoint.

16. What is the use of Redis in .NET applications?

    • Answer: Redis is used as a caching layer to improve application performance by reducing database queries.

17. How do you handle concurrency in .NET Core?

    • Answer: Using lock statements, SemaphoreSlim, Mutex, or optimistic concurrency with EF Core.

18. What is gRPC and how does it work in .NET?

    • Answer: gRPC is a high-performance RPC framework using Protobuf and HTTP/2, ideal for microservices communication.

19. What is CORS and how do you enable it in .NET Core?

    • Answer: CORS (Cross-Origin Resource Sharing) allows web applications to access resources from different origins. It is enabled using app.UseCors().

20. How do you handle exceptions in ASP.NET Core?

    • Answer: Using try-catch, middleware (UseExceptionHandler), or global exception handling with custom middleware.

21. What is API Versioning and how do you implement it in .NET Core?

    • Answer: API versioning helps manage multiple API versions. It is implemented using Microsoft.AspNetCore.Mvc.Versioning.

22. How do you implement background tasks in .NET Core?

    • Answer: Using IHostedService, BackgroundService, or third-party libraries like Hangfire.

23. What is Blazor and how does it compare to Angular or React?

    • Answer: Blazor is a .NET-based framework for building web applications using C#. Unlike Angular/React, it does not require JavaScript.

24. How do you secure sensitive data in .NET applications?

    • Answer: Using encryption, secrets management, Azure Key Vault, and securing API keys.

25. What is SignalR and how does it work in .NET Core?

    • Answer: SignalR is a library for real-time web applications, enabling live updates using WebSockets or other transports.

These technical .NET Full Stack interview questions cover backend (ASP.NET Core, EF Core), frontend (Blazor, Angular), databases, security, performance, and microservices to help prepare for .NET development roles.