A complete, structured guide for mastering .NET and C# at an intermediate and senior level.
This documentation is divided into five main pillars, each containing detailed technical topics, best practices, and interview-grade explanations.

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1. C# Language & Core Programming

This section builds a strong foundation in the C# language and its underlying concepts.

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C# Language Fundamentals

• Data types, variables, and constants
• Value types vs reference types
• Type casting and conversions
• Nullable types
• var, dynamic, and object
• Strings and interpolation
• Control flow (if, switch, loops)
• Arrays and collections
• Structs and enums
• readonly and const
• Pattern matching
• Tuples and deconstruction
• Indexers and ranges (^, ..)
• XML documentation

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Object-Oriented Programming (OOP)

• Classes and objects
• Inheritance and polymorphism
• Abstract classes and interfaces
• Encapsulation and access modifiers
• Constructors and destructors
• Static members and singletons
• Sealed classes
• Partial classes and records
• Method hiding (new)
• Virtual vs override

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Advanced C# Concepts

• Delegates and events
• Lambda expressions
• Extension methods
• Reflection and attributes
• Generics and constraints
• Nullable reference types
• Expression-bodied members
• Records and immutability
• Operator overloading
• File-scoped namespaces
• Global using directives
• Span<T> and Memory<T>

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2. Collections, LINQ & Asynchronous Programming

Master the tools that make .NET development fast, expressive, and scalable.

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Collections & Generics

• Arrays, Lists, Dictionaries, HashSet, Queues, Stacks
• ReadOnlyCollection and concurrent collections
• Immutable collections

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LINQ

• Query syntax vs method syntax
• Filtering, projection, grouping, joining
• Aggregation functions
• Deferred vs immediate execution
• Custom extension methods
• Parallel LINQ (PLINQ)

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Asynchronous Programming

• Tasks and threads
• async and await pattern
• Task-based Asynchronous Pattern (TAP)
• Task.WhenAll and Task.WhenAny
• Synchronization (lock, SemaphoreSlim)
• Cancellation tokens
• Deadlocks and prevention
• Background services and hosted services
• Using ValueTask for performance

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3. ASP.NET Core, Web API, EF Core & Architecture

This section covers the main components of building robust backend applications with .NET.

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.NET Core Fundamentals

• CLR, JIT compilation, GC
• Project structure (Program.cs, hosting model)
• Kestrel web server
• Middleware pipeline
• Configuration providers
• Dependency injection system

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ASP.NET Core MVC & Razor

• Controllers, views, and models
• Razor syntax, layouts, partial views
• Tag helpers
• Model binding and validation
• ViewData, ViewBag, TempData
• Anti-forgery tokens

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ASP.NET Core Web API

• [ApiController] basics
• Routing and attribute routing
• Action results and response shaping
• Swagger/OpenAPI
• File uploads and streaming
• Pagination, filtering, sorting
• API throttling and rate limiting

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Entity Framework Core (EF Core)

• DbContext and DbSet
• Code-first migrations
• Relationship configuration
• Loading strategies (lazy/eager/explicit)
• Transactions and concurrency
• Change tracking
• Raw SQL execution
• Repository and Unit of Work patterns

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SQL Server & Data Design

• Normalization vs denormalization
• Indexes and keys
• Joins and query optimization
• Stored procedures, views, triggers
• CTEs and window functions

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4. Security, Testing, Performance & Deployment

A senior .NET developer must excel in building secure, performant, and well-tested systems.

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Authentication & Authorization

• ASP.NET Core Identity
• Claims and roles
• Policy-based authorization
• JWT authentication
• OAuth2 and OpenID Connect
• Refresh tokens
• External providers

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Validation & Middleware

• Data annotations
• Custom validation attributes
• FluentValidation
• Custom middleware
• Filters (resource, action, exception)

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Performance & Caching

• In-memory and distributed caching
• Response and output caching
• Compression middleware
• EF query optimization
• BenchmarkDotNet
• Asynchronous I/O

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Logging & Monitoring

• ILogger<T> usage
• Serilog, NLog integration
• Centralized logging (Seq, ELK, App Insights)
• Distributed tracing with OpenTelemetry
• Health checks

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Testing

• xUnit, NUnit, MSTest
• Moq for mocking
• FluentAssertions
• EF Core in-memory testing
• Integration testing with TestServer

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5. Microservices, Messaging, Cloud & System Design

Master modern distributed system design with .NET and cloud platforms.

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Microservices & Distributed Systems

• Microservices principles
• Communication patterns (HTTP, gRPC)
• API gateways (Ocelot, YARP)
• Resilience with Polly (retry, circuit breaker)
• Distributed tracing and correlation IDs

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Messaging & Background Jobs

• RabbitMQ, Kafka, Azure Service Bus
• Background workers (IHostedService)
• Worker Service templates
• Hangfire / Quartz.NET scheduling
• Event-driven design

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Cloud Deployment & DevOps

• Docker and multi-stage builds
• Kubernetes basics
• CI/CD pipelines (GitHub Actions, Azure DevOps)
• Monitoring (Prometheus, Grafana)
• Deployment slots and rolling updates

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Architecture & System Design

• Clean Architecture
• Onion Architecture
• CQRS and Mediator pattern
• Event Sourcing and DDD
• Monolith vs microservices
• Load balancing and caching
• Database sharding and partitioning
• Idempotent API design

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Start Learning

Choose a topic below to begin your .NET learning journey.