C# Warrior : Learn .NET Core Basic To Advance

Want to write clean, scalable, and maintainable C# code ? Let’s break down the OOP fundamentals and the SOLID design principles — with real-world examples, explanations, and code snippets you can copy-paste into your next project. 📚 Table of Contents 🎯 OOP fundamentals 🔒 Encapsulation 🎭 Abstraction 🧬 Inheritance 🔄 Polymorphism 🏗️ SOLID principles S — Single Responsibility Principle O — Open/Closed Principle L — Liskov Substitution Principle I — Interface Segregation Principle D — Dependency Inversion Principle 🛒 Mini e-commerce scenario (tying everything together) 💡 Next steps (make it runnable!) 🎯 1. OOP Fundamentals 🔒 Encapsulation — protect your object’s state 👉 Idea: Don’t let anyone mess with your object’s internals. Provide safe, controlled methods. Use-case: An Order should manage its own items and discounts. public class Order { private readonly List<OrderItem> _items = new(); private decimal _discountPercent; publ...

Azure Entra ID (formerly Azure Active Directory) is Microsoft’s cloud-based identity and access management (IAM) service. It helps secure apps, APIs, and services by managing authentication (who you are) and authorization (what you can do) . 🔹 1. Key Concepts Tenant : A dedicated instance of Entra ID for your organization. App Registration : Register apps to integrate with Entra ID for authentication. Authentication : Verifying user or service identity (via username, password, certificate, token). Authorization : Granting permissions (roles/scopes) after authentication. Tokens : ID Token → User identity (used in login). Access Token → Grants access to APIs. Refresh Token → Get new tokens without logging in again. 🔹 2. Authentication Flows Authorization Code Flow (with PKCE) – Secure for web & mobile apps. Client Credentials Flow – Service-to-service authentication (no user). Device Code Flow – Used on devices without browsers (IoT, CLI). Implicit Flo...

  🟢 What is Azure Cosmos DB? A globally distributed, multi-model, NoSQL database service . Designed for low latency, high availability, and global scalability . Supports multiple APIs: SQL (Core), MongoDB, Cassandra, Gremlin (Graph), Table API . 👉 Think of it as a database that automatically scales across the globe . 🟢 Key Concepts Account → Database → Container → Items Partition Key → spreads data evenly across physical partitions. Request Units (RUs) → performance currency (every operation consumes RUs). Consistency Levels → trade-off between performance and accuracy: Strong, Bounded Staleness, Session, Consistent Prefix, Eventual. Change Feed → stream of inserts/updates in order. 🟢 Partition Key (Most Asked in Interviews) Good partition key : high cardinality, evenly distributes load. Bad partition key : low cardinality (e.g., true/false, country code). Can use synthetic keys (e.g., CustomerId + Date ). 👉 Interviewers love to ask: “What happe...

🟢 Azure Monitor ✅ What is it? A unified monitoring service in Azure for metrics, logs, and alerts. Collects data from apps, VMs, containers, databases, storage, networking, etc. Acts as the foundation for observability in Azure. 👉 Think of Azure Monitor as the big umbrella → it collects & stores monitoring data. ✅ Key Components Metrics → numerical time-series data (CPU %, memory, requests/sec). Logs → detailed event & diagnostic data (stored in Log Analytics). Alerts → notifications when thresholds are crossed. Dashboards → visualize metrics/logs. Workbooks → custom interactive reports. 🟢 Azure Application Insights (App Insights) ✅ What is it? An APM (Application Performance Monitoring) service under Azure Monitor. Monitors application performance, failures, requests, dependencies, and usage . Works with .NET, Java, Node.js, Python, and front-end JS apps . 👉 Think of App Insights as the “inside view” of your app , while Azure Monitor is t...

🟢 Azure Service Bus ✅ What is it? A fully managed enterprise message broker . Used for asynchronous communication between apps and services. Ensures reliable delivery, ordering, and advanced messaging patterns. 👉 Think of it as a postal service → messages are sent, stored, and delivered reliably. ✅ Key Features Queues → Point-to-point messaging (1 sender → 1 receiver). Topics & Subscriptions → Publish/Subscribe model (1 sender → many receivers). Sessions → Ordered message processing (FIFO). Dead-letter Queue (DLQ) → Stores undeliverable messages. Duplicate Detection → Avoid processing the same message twice. Scheduled Delivery & Deferral → Send messages to be delivered later. ✅ Example Use Cases Order processing systems. Background job processing. Microservices communication. 🟢 Azure Event Hub ✅ What is it? A big data streaming platform and event ingestion service . Designed to handle millions of events per second . Best for real-time ana...

🟢 What is Azure Storage? A cloud-based storage service for storing different types of data: Unstructured (images, videos, docs). Semi-structured (JSON, logs). Structured (tables). Highly available, durable (replicated), and scalable. 👉 Think of it as different storage buckets under one umbrella. 🟢 Core Azure Storage Services Blob Storage → store unstructured data (images, docs, backups, logs). Access tiers: Hot, Cool, Archive (cost vs. access trade-off). Supports large file uploads (up to TBs). Use cases: CDN, backups, static website hosting. Table Storage → NoSQL key-value store. Schemaless → good for semi-structured data. Use cases: metadata, logs, user profile storage. Queue Storage → message queuing for async communication. Simple producer-consumer pattern . Use cases: background jobs, task scheduling. Max message size: 64 KB. File Storage (Azure Files) → fully managed SMB file shares in the cloud. Mountable by Windows, Linux, macO...

🟢 What is Azure Key Vault? A cloud service for securely storing and accessing secrets, keys, and certificates . Removes the need to keep secrets (like connection strings, passwords, API keys) inside code or config files. Provides centralized secret management, encryption, and access control . 👉 Think of it like a secure password manager but for your applications. 🟢 Key Features Secrets → store text values (e.g., DB connection string, API key). Keys → store cryptographic keys (RSA, EC) for encryption, signing. Certificates → store/manage SSL/TLS certificates. Access Control → Access Policies (older model). Azure RBAC (modern, preferred). Integration → works with App Service, Functions, AKS, VMs, SQL DB, etc. Logging → audit who accessed secrets via Azure Monitor / Diagnostic Logs. 🟢 Why Use Key Vault? Security → secrets are encrypted with HSM (Hardware Security Modules). Compliance → meet industry standards (PCI-DSS, ISO, GDPR). Automation → aut...

🟢 What is Azure App Service? A Platform as a Service (PaaS) in Azure to host web apps, APIs, and mobile backends . You focus on writing code → Azure handles infrastructure, scaling, patching, and security . Supports multiple frameworks: .NET, Java, Python, Node.js, PHP, Ruby, Docker containers . 👉 Think of it like: “Just deploy your code, we’ll handle the servers.” 🟢 Key Features Deployment Slots → test in staging before swapping to production (zero-downtime). Scaling → Vertical scaling → increase CPU/RAM. Horizontal scaling → add more instances. Authentication & Authorization → built-in support for Entra ID (Azure AD) , Google, Facebook, GitHub. DevOps Integration → CI/CD with GitHub Actions, Azure DevOps, Bitbucket, or FTP . Monitoring → Deep integration with Application Insights for performance, exceptions, and telemetry. Custom Domains & SSL → easy binding of your own domain with HTTPS. Networking → VNET integration, hybrid connections,...

Azure Functions is a serverless compute service in Azure. You write code, and Azure runs it automatically whenever an event triggers it. No need to manage servers or infrastructure. 🟢 1. What is Azure Function? Serverless → pay only for execution time, no VM management. Runs small units of code ("functions") in response to triggers. Supports multiple languages (C#, JavaScript, Python, Java, PowerShell, etc.). 🟢 2. Key Concepts Function App → Container for one or more functions (like a project). Trigger → Event that starts a function (HTTP request, Timer, Blob, Queue, Event Hub, etc.). Binding → Way to connect to other services without boilerplate code. Input Binding : brings data into function. Output Binding : sends data from function. Consumption Plan → Auto-scales and pay-per-use. Premium/Dedicated Plan → Pre-warmed instances, VNET support, higher performance. 🟢 3. Types of Triggers HTTP Trigger → run on API calls. Timer Trigger → run ...

When you deploy apps to the cloud, monitoring and observability are critical. Azure Application Insights (App Insights) is a powerful tool that helps you monitor, diagnose, and optimize your applications. In this blog, we’ll cover: ✅ What Azure App Insights is ✅ Key concepts (Telemetry, KQL, Instrumentation Key vs Connection String, Sampling) ✅ Integration with various Azure services ✅ Real-world setup examples (App Service, Function App, API, Containers, Key Vault, Cosmos DB, Service Bus) ✅ Best practices for developers 🌟 What is Azure Application Insights? Azure Application Insights is an Application Performance Monitoring (APM) service under Azure Monitor . It allows you to: Collect telemetry: requests, dependencies, exceptions, traces, custom events Diagnose performance issues (slow requests, failed calls, memory leaks) Visualize health in dashboards Write powerful queries using Kusto Query Language (KQL) Integrate with DevOps pipelines (alerts, dashboards, rel...

This article shows how to: Register your API in Microsoft Entra (Azure AD) and expose a scope. Register clients (daemon and web client) and grant permissions. Protect a .NET Web API (ASP.NET Core) using Microsoft.Identity.Web . Call the API from: a daemon/service using client credentials a backend that performs On-Behalf-Of (OBO) to call a downstream API Replace placeholders like YOUR_TENANT_ID , API_CLIENT_ID , CLIENT_APP_ID , and CLIENT_SECRET with actual values from the portal. ✳️ Portal steps (brief) Register API ( MyProductApi ) Azure Portal → Microsoft Entra ID → App registrations → New registration → MyProductApi Note: Application (client) ID → API_CLIENT_ID , Directory (tenant) ID → YOUR_TENANT_ID Expose an API App → Expose an API → Set Application ID URI to api://{API_CLIENT_ID} (default) or https://contoso.com/my-api Add a scope : Scope name: access_as_user Admin consent display name: Access MyProductApi as user Who can consent: Admins a...

When working with Microsoft Entra (formerly Azure Active Directory), you’ll hear terms like App Registration, Tenant, Client ID, Audience, Scopes, Roles, Tokens, OBO flow , and more. If you’re new, it can feel overwhelming. This guide breaks down every key term and concept , with definitions, examples, and how they connect when you onboard and consume a new API. 🔹 1. Tenant Definition : A tenant in Entra ID is your organization’s dedicated, isolated instance of Microsoft Entra. Think of it like : Your company’s identity directory. Example : contoso.onmicrosoft.com is a tenant for Contoso Ltd. 🔹 2. App Registration Definition : The process of registering an application in Entra to give it an identity and permission to use Microsoft identity platform. Why needed : Without registration, Entra doesn’t know about your app. What it creates : Application (Client) ID – unique identifier for your app Directory (Tenant) ID – your organization’s ID Types of apps : Web ...

Errors, Issues, and How to Fix Them (Step-by-Step Guide) Azure Functions are powerful for building serverless apps, but when you start integrating them with services like Azure Storage, Service Bus, Cosmos DB, Key Vault, or Application Insights , things often break. In this blog, we’ll explore: ✅ Why errors happen while integrating Function Apps ✅ A 7-step troubleshooting playbook (works for almost all issues) ✅ Common service-specific errors and fixes ✅ Useful commands, logs, and code snippets ✅ Quick error–fix cheat sheet 🔎 Why do errors happen in Azure Functions? Most integration issues can be traced to one of these: Missing/invalid App Settings – wrong connection strings, missing keys. Binding/extension mismatches – incompatible runtime/SDK versions. Identity & RBAC – Function App doesn’t have access to the resource. Networking/firewall – blocked by VNet or private endpoints. Lack of logs – no monitoring to catch the root cause. 🛠 7-Step Troublesho...

When you start working with .NET and C#, one of the biggest advantages is that you don’t need to manually manage memory like in C or C++. The Garbage Collector (GC) does most of the work for you. But here’s the catch — not everything is managed automatically. Some resources like files, database connections, sockets, and native memory still need special handling. This blog will help you understand: ✔ How the GC works ✔ What are managed vs unmanaged resources ✔ The difference between Dispose , Finalize , and using ✔ The Dispose pattern with examples ✔ Best practices every C# developer should know 1) How Garbage Collection Works in .NET Managed resources → Normal .NET objects (string, List, etc.). GC frees them automatically. Unmanaged resources → External resources like file handles, database connections, sockets, native memory. GC cannot clean them up — you must do it. 👉 GC uses a Generational Model for performance: Gen 0 : Short-lived objects (local variables, t...

Caching is one of the most important performance boosters in modern .NET applications. Done right, it reduces database hits, improves response times, saves costs, and scales apps easily. In this post, we’ll cover popular caching strategies in .NET with detailed examples and comments . 1️⃣ In-Memory Caching ( IMemoryCache ) Best for: Single-server apps, small data, per-instance cache. Storage: Inside the app process memory. Downside: Cache is lost if app restarts, and not shared across multiple servers. Example // Program.cs builder.Services.AddMemoryCache(options => { options.SizeLimit = 1024; // optional global limit }); public class WeatherService { private readonly IMemoryCache _cache; private readonly IHttpClientFactory _http; public WeatherService(IMemoryCache cache, IHttpClientFactory http) { _cache = cache; _http = http; } public async Task<WeatherDto> GetWeatherAsync(string city) { var key = $...