RemoveFun747 shares insights and community-driven advice for developers transitioning from legacy .NET Framework 4.8 to modern .NET 9, including learning resources and practical architectural considerations.

Transitioning from .NET Framework 4.8 to Modern .NET (Core/9): Advice & Resources

Authored by RemoveFun747 and the r/dotnet community

If you’re moving from maintaining legacy applications built on .NET Framework 4.8 to developing with .NET 9, there are significant differences to understand. This post, featuring community contributions, outlines what’s changed, how to adapt, and where to learn the modern .NET stack.

Key Changes and Advantages

  • Modularity & Dependency Injection:
    • Modern .NET (from Core onwards) adopts a modular structure. Services are brought in as needed via dependency injection. Accessing HttpContext, injecting custom interfaces, caching, and setting up the database context are all managed through DI containers.
  • Performance Improvements:
    • Major performance enhancements in .NET Core/.NET 5+ over Framework 4.8.
  • Cross-platform Development:
    • Develop and run .NET 9 applications on Windows, Linux, and macOS using VSCode or Visual Studio. Choose the correct SDK for your OS and CPU.
  • NuGet Ecosystem:
    • Thousands of packages available; many maintain backwards compatibility.
  • Diverse App Types:
    • Build games, web apps, APIs, mobile apps, IoT software, and more with the evolving frameworks.
  • Containerization:
    • Deploy apps easily with Docker. Create self-contained executable containers.
  • C# Language Modernization:
    • New features (like top-level statements, global usings, record types) reduce boilerplate code.
  • YouTube Channel: Tim Corey explains modern .NET concepts in accessible tutorials.
  • Books: C# 12 in a Nutshell (Albahari) covers up-to-date language features.
  • Course Platforms: Udemy has multiple top-rated .NET Core/.NET 9 application courses.
  • Experimentation: Build a web application from scratch using ASP.NET Core and Blazor to practically apply modern concepts. Comparing this to old codebases highlights differences.

Popular Architectural Patterns & Buzzwords

  • Clean Architecture: Separate software layers for maintainability.
  • Domain Driven Design (DDD): Design around business entities, not technology constraints.
  • CQRS: Command Query Responsibility Segregation governs data flow.
  • Microservices: Isolate business domains into deployable services with separate infrastructure.
  • Monolith: Single large application (less common in new projects but still valid).
  • Entity Framework (EF): Modern ORM for C#—write models as C# classes, use LINQ for data access.

Upgrading Process and Tips

  • Prototype a modern web app using ASP.NET Core and Blazor.
  • Use search engines and the above learning resources to cover unfamiliar topics as you build.
  • Focus initially on project setup, dependency injection, configuration, and middleware concepts.
  • Study the architectural ‘one-liner’—how each app is structured (e.g., “.NET 9, DDD, CQRS, EF, Monolith”).

Community Encouragement

  • The learning curve is manageable with consistent practice.
  • Ask further questions in the community.
  • Be proactive and hands-on.
  • Stay open to change—AI and the Microsoft ecosystem are evolving rapidly.

Editor and Community Notes

  • Many differences between .NET Framework 4.x and .NET 5+ are architectural and infrastructural.
  • There are nearly ten years of evolution to study; don’t try to learn it all at once.
  • Moderators note: Please follow subreddit rules and search for already-answered questions to avoid duplicates.

Author: RemoveFun747, with responses from the r/dotnet community

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