Singleton vs Static in .NET: Key Differences Explained

 When working with .NET applications, one of the most common confusions developers face is the difference between Singleton and Static. Both provide global access, but they are not the same thing. In this article, we will dive deep into the definition, usage, and differences between Singleton and Static in .NET with real-world examples.

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✅ What is Singleton in .NET?

A Singleton is a design pattern that ensures only one instance of a class is created throughout the application’s lifetime. It provides a global point of access while still following object-oriented principles like inheritance, interfaces, and polymorphism.

Example: Logger Singleton

public sealed class Logger
{
    private static readonly Lazy<Logger> instance =
        new Lazy<Logger>(() => new Logger());

    private Logger() { } // private constructor

    public static Logger Instance => instance.Value;

    public void Log(string message)
    {
        Console.WriteLine($"Log: {message}");
    }
}

Usage:

Logger.Instance.Log("Application started");

👉 Real-world use cases of Singleton:

• Database connection manager

• Configuration manager

• Logging service

• Caching mechanisms

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✅ What is Static in .NET?

A Static class in .NET is a special class that cannot be instantiated. All its members (methods, variables, properties) are static and directly accessible via the class name.

Example: Static Helper Class

public static class MathHelper
{
    public static int Square(int number) => number * number;
}

Usage:

int result = MathHelper.Square(5); // 25

👉 Real-world use cases of Static:

• Utility methods (e.g., math calculations, string helpers)

• Constants (PI, AppVersion)

• Helper classes without state

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🔑 Key Differences Between Singleton and Static in .NET

Feature	Singleton	Static
Definition	Design pattern	Language keyword
Object creation	One instance created	No instantiation
Memory lifetime	Managed by Garbage Collector	Lives entire application domain
Supports OOP (Inheritance, Interfaces, Polymorphism)	✅ Yes	❌ No
Thread safety	Needs handling (lock, Lazy<T>)	CLR ensures thread-safe initialization
State management	Maintains instance state	Global state only
Best use case	Services, configurations, DB connections	Utilities, constants, helper methods

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🧠 When to Use Singleton vs Static in .NET

• Use Singleton when:

  • You need a single object with state.

  • You want to implement OOP features like interfaces or inheritance.

  • Example: Logging service, configuration manager, database connection.

• Use Static when:

  • You need stateless utility functions.

  • You want a class with only constants or helper methods.

  • Example: Math functions, string helpers, conversion utilities.

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📌 Final Thoughts

Both Singleton and Static provide global access in .NET, but they solve different problems.

• Singleton is best for stateful, OOP-compliant services.

• Static is ideal for stateless utility functions and constants.

Choosing the right one depends on whether your requirement involves state + OOP (go for Singleton) or just global utility (go for Static).

Design Patterns Explained: GoF & Modern Patterns with Real-World Examples

In software development, Design Patterns act as proven solutions to common problems. Instead of reinventing the wheel, developers can apply these reusable patterns to build scalable, maintainable, and robust applications.

This article explains Gang of Four (GoF) design patterns and also highlights modern design patterns widely used in cloud, microservices, and enterprise systems.

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📌 What Are Design Patterns?

Design patterns are general, reusable solutions to recurring software problems. They are not code snippets but guidelines on how to solve design challenges effectively.

Benefits of using design patterns:

• Improve code reusability & readability

• Promote best practices & standardization

• Reduce development & maintenance time

• Help in team communication (common vocabulary)

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🏛 Gang of Four (GoF) Design Patterns

The GoF introduced 23 design patterns in their famous book "Design Patterns: Elements of Reusable Object-Oriented Software".

They are categorized into three groups:

1. Creational Patterns – Object creation

Help in creating objects without exposing the creation logic.

• Singleton → Ensures only one instance exists.

  public sealed class Logger
  {
      private static readonly Logger _instance = new Logger();
      private Logger() { }
      public static Logger Instance => _instance;
  }
  

  ✅ Used in logging, caching, config management.

• Factory Method → Subclasses decide object creation.

• Abstract Factory → Create families of related objects.

• Builder → Step-by-step object construction.

• Prototype → Clone objects without depending on their class.

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2. Structural Patterns – Class & object composition

Define how objects are composed for flexibility.

• Adapter → Converts one interface into another.
  ✅ Example: Wrapping an old payment gateway API to fit into a new e-commerce app.

• Decorator → Add responsibilities dynamically.

• Facade → Provide a simple interface to a complex system.

• Composite → Treat individual & group objects uniformly (tree structure).

• Proxy → Control access (like lazy loading, security).

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3. Behavioral Patterns – Object communication

Define how objects interact & responsibilities are distributed.

• Observer → One-to-many dependency.

  public interface IObserver { void Update(string msg); }
  public class User : IObserver
  {
      private string _name;
      public User(string name) => _name = name;
      public void Update(string msg) => 
  Console.WriteLine($"{_name} got update: {msg}");
  }
  public class NotificationService
  {
      private List<IObserver> observers = new();
      public void Subscribe(IObserver o) => observers.Add(o);
      public void Notify(string msg)
      {
          foreach (var o in observers) o.Update(msg);
      }
  }
  

  ✅ Used in push notifications, event-driven systems.

• Strategy → Choose algorithm at runtime.

• Command → Encapsulate actions as objects.

• State → Change behavior based on object state.

• Mediator, Memento, Interpreter, Visitor, Template Method, Chain of Responsibility, Iterator.

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🚀 Modern / New Design Patterns (Beyond GoF)

Today’s software systems (Cloud, Microservices, Big Data, AI) need patterns beyond GoF. Here are some important ones:

1. Dependency Injection (DI)

• Promotes loose coupling by injecting dependencies instead of creating them inside a class.

• Widely used in .NET Core, Spring Boot, Angular.

  public class OrderService
  {
      private readonly IPaymentGateway _paymentGateway;
      public OrderService(IPaymentGateway paymentGateway)
   => _paymentGateway = paymentGateway;
      public void PlaceOrder() => _paymentGateway.Process();
  }
  

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2. Repository Pattern

• Abstracts database access to keep business logic independent.

• Used in DDD (Domain-Driven Design) and enterprise apps.

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3. CQRS (Command Query Responsibility Segregation)

• Separates read and write operations for better scalability.

• Common in microservices + event sourcing.

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4. Saga Pattern (Microservices)

• Handles distributed transactions across microservices.

• Uses event-driven orchestration or choreography to maintain consistency.

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5. Event Sourcing

• State changes are stored as events (not just final values).

• Used in banking, e-commerce order history, blockchain-like systems.

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6. Circuit Breaker Pattern

• Prevents cascading failures by stopping requests to a failing service.

• Implemented in Polly (.NET), Resilience4j (Java).

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7. API Gateway Pattern

• Acts as a single entry point for microservices.

• Handles routing, load balancing, authentication, caching.

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8. Strangler Fig Pattern

• Gradually replaces legacy systems by routing new features to modern services while
   old ones still run.

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🔑 Conclusion

• GoF Patterns are still foundational for object-oriented design.

• Modern patterns are essential for cloud, distributed systems, and microservices.

• By combining both, developers can build scalable, reliable, and future-proof applications.

REST in .NET Explained: A Complete Guide with Examples

If you are working with ASP.NET Core Web API, you will frequently hear the term REST API. But what does REST actually mean, and how do you implement it properly in .NET? Let’s break it down step by step with practical examples.

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What is REST?

REST stands for Representational State Transfer. It is an architectural style for building distributed systems, especially web services, that communicate over HTTP.

Key REST principles:

• Resources, not actions → Think in nouns like /api/books instead of verbs like /api/getBooks.

• HTTP methods define actions

  • GET → fetch data

  • POST → create

  • PUT → replace

  • PATCH → partial update

  • DELETE → remove

• Stateless → Each request contains everything needed. The server does not store session data.

• Multiple representations → Same resource can be returned in JSON, XML, etc.

• Cacheable → Responses should support caching for performance.

In short: REST APIs are about clean URLs, proper HTTP methods, and stateless communication.

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REST in .NET

In ASP.NET Core, REST APIs are built using:

• Controllers or Minimal APIs

• Attributes like [HttpGet], [HttpPost], [HttpPut], [HttpDelete]

• Model binding & validation

• ActionResult / IActionResult for proper HTTP responses

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Example: Building a REST API in ASP.NET Core

1. Define a Model (DTO)

public record BookDto
{
    public int Id { get; init; }
    public string Title { get; init; } = "";
    public string Author { get; init; } = "";
}

2. In-memory Repository

public interface IBookRepository
{
    Task<IEnumerable<BookDto>> GetAllAsync();
    Task<BookDto?> GetByIdAsync(int id);
    Task<BookDto> CreateAsync(BookDto book);
    Task UpdateAsync(BookDto book);
    Task DeleteAsync(int id);
}

public class InMemoryBookRepository : IBookRepository
{
    private readonly List<BookDto> _books = new();
    private int _nextId = 1;

    public Task<IEnumerable<BookDto>> GetAllAsync() =>
        Task.FromResult(_books.AsEnumerable());

    public Task<BookDto?> GetByIdAsync(int id) =>
        Task.FromResult(_books.FirstOrDefault(b => b.Id == id));

    public Task<BookDto> CreateAsync(BookDto book)
    {
        var created = book with { Id = _nextId++ };
        _books.Add(created);
        return Task.FromResult(created);
    }

    public Task UpdateAsync(BookDto book)
    {
        var idx = _books.FindIndex(b => b.Id == book.Id);
        if (idx >= 0) _books[idx] = book;
        return Task.CompletedTask;
    }

    public Task DeleteAsync(int id)
    {
        var book = _books.FirstOrDefault(x => x.Id == id);
        if (book != null) _books.Remove(book);
        return Task.CompletedTask;
    }
}

3. Create a REST Controller

[ApiController]
[Route("api/[controller]")]
public class BooksController : ControllerBase
{
    private readonly IBookRepository _repo;

    public BooksController(IBookRepository repo) => _repo = repo;

    [HttpGet]
    public async Task<ActionResult<IEnumerable<BookDto>>> GetAll()
    {
        var items = await _repo.GetAllAsync();
        return Ok(items);
    }

    [HttpGet("{id}")]
    public async Task<ActionResult<BookDto>> Get(int id)
    {
        var book = await _repo.GetByIdAsync(id);
        return book is null ? NotFound() : Ok(book);
    }

    [HttpPost]
    public async Task<ActionResult<BookDto>> Create(BookDto dto)
    {
        var created = await _repo.CreateAsync(dto);
        return CreatedAtAction(nameof(Get), new { id = created.Id }, created);
    }

    [HttpPut("{id}")]
    public async Task<IActionResult> Update(int id, BookDto dto)
    {
        if (id != dto.Id) return BadRequest();
        var existing = await _repo.GetByIdAsync(id);
        if (existing is null) return NotFound();

        await _repo.UpdateAsync(dto);
        return NoContent();
    }

    [HttpDelete("{id}")]
    public async Task<IActionResult> Delete(int id)
    {
        var existing = await _repo.GetByIdAsync(id);
        if (existing is null) return NotFound();

        await _repo.DeleteAsync(id);
        return NoContent();
    }
}

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RESTful API Best Practices in .NET

✅ Use plural nouns for resources → /api/books
✅ Return correct status codes → 200, 201, 204, 404, 400
✅ Implement input validation and return problem details
✅ Add Swagger/OpenAPI for documentation
✅ Support paging, filtering, sorting with query parameters
✅ Use JWT authentication for secure APIs
✅ Apply versioning (e.g., /api/v1/books)

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When NOT to Use REST

• Use gRPC for high-performance internal service-to-service communication.

• Use GraphQL when clients need flexible queries and avoid multiple endpoints.

REST is best when:

• You want simplicity

• Standard HTTP semantics are enough

• Clients benefit from caching

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Conclusion

In .NET, REST APIs are built using ASP.NET Core’s Web API framework. By following REST principles—resources, HTTP verbs, statelessness, proper status codes—you can build clean, scalable, and maintainable APIs.

Start with a simple controller, use proper response codes, and then enhance with authentication, versioning, and documentation. That’s how you make a professional REST API in .NET.

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Complete Guide to Azure Functions with Example, Step-by-Step Setup, and Interview Questions

🌟 What are Azure Functions?

Azure Functions is a serverless compute service provided by Microsoft Azure. It allows developers to run small pieces of code, called functions, without worrying about infrastructure.

Instead of setting up servers, scaling manually, or managing infrastructure, you only write the code, and Azure handles the rest.

👉 You pay only for execution time, making it cost-effective and scalable.

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🔧 Key Concepts in Azure Functions

• Trigger → Defines how the function starts (e.g., HTTP request, Timer, Queue, Blob upload).

• Input Binding → Brings data into the function.

• Output Binding → Sends processed data out (e.g., to CosmosDB, Storage, Service Bus).

📌 Example: An HTTP Trigger Function can process user input and save it to CosmosDB.

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🛠 Step-by-Step Example: Create an Azure Function

Let’s build a C# Azure Function that greets users.

1️⃣ Prerequisites

• An Azure subscription

• Visual Studio 2022 or VS Code with Azure Functions extension

• Azure Functions Core Tools (for CLI usage)

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2️⃣ Create a Function in VS Code

1. Open VS Code → Install Azure Functions Extension.

2. Click Azure Logo → Create New Project.

3. Select C# as language.

4. Choose HTTP trigger.

5. Name it GreetFunction.

6. Set Authorization level → Anonymous.

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Note : Please Check and debug the code (If not working check latest code in Internet)

3️⃣Add Function Code

using System.IO;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;

public static class GreetFunction
{
    [FunctionName("GreetFunction")]
    public static IActionResult Run(
        [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");

        string name = req.Query["name"];

        if (string.IsNullOrEmpty(name))
        {
            return new BadRequestObjectResult("Please pass a name in the query string.");
        }

        return new OkObjectResult($"Hello {name}, Welcome to Azure Functions!");
    }
}

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4️⃣ Run Locally

• Press F5 to run.

• Open browser:

  http://localhost:7071/api/GreetFunction?name=Cherry
  

• Output:

  Hello Cherry, Welcome to Azure Functions!
  

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5️⃣ Deploy to Azure

1. In VS Code → Right-click project → Deploy to Function App.

2. Select subscription & resource group.

3. Create a new Function App.

4. After deployment → Test the live URL:

   https://<yourappname>.azurewebsites.net/api/GreetFunction?name=Cherry
   

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6️⃣ Monitor & Logs

• In Azure Portal → Function App → Monitor,

• Track logs, execution count, and performance metrics.

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⚡ Real-World Use Cases of Azure Functions

• Image Processing → Triggered when a blob is uploaded.

• Email Notifications → Triggered by Queue messages.

• Scheduled Jobs → Using Timer Triggers (CRON).

• ETL Pipelines → Streaming data with Event Hub.

• IoT Applications → Processing telemetry events in real-time.

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🎯 Top Azure Functions Interview Questions

Basics

1. What are Azure Functions, and how do they differ from WebJobs?

2. Explain Triggers and Bindings.

3. What are the different hosting plans (Consumption, Premium, Dedicated)?

4. What is the cold start problem, and how do you reduce it?

5. Difference between Azure Functions and Azure Logic Apps.

Development & Deployment

6. How do you debug Azure Functions locally?

7. How can one Azure Function call another?

8. How do you secure Azure Functions? (API Keys, Azure AD, Managed Identity)

9. How do you manage secrets/configuration? (App settings, Azure Key Vault)

10. What is a Durable Function, and when should you use it?

Advanced

11. How do you monitor and log executions?

12. Can Azure Functions run in a VNET?

13. How does scaling work in Azure Functions?

14. How do retries work in queue-triggered functions?

15. What are Durable Entities in Azure Durable Functions?

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✅ Conclusion

Azure Functions is a powerful way to build event-driven, serverless applications on Azure.

• Easy to create with triggers and bindings.

• Cost-effective with pay-per-use pricing.

• Scales automatically with demand.

Whether you’re preparing for an interview or building real-world microservices, mastering Azure Functions gives you a strong edge in modern cloud development.

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