将ASP.NET Core（.NET Framework）升级至ASP.NET Core（.NET Core）相关咨询

Great question—this is a super common point of confusion when moving between .NET Core versions! Let’s break this down clearly:

核心结论：通常不需要完全迁移到新应用 #

Once you’ve updated all incompatible third-party libraries, you can almost always upgrade your existing base application directly—no need to rebuild from scratch. That said, there are a few key checks and minor adjustments you’ll likely need to make first.

直接升级的关键步骤（必做） #

• Update your project’s Target Framework Moniker (TFM)
  Open your .csproj file and change the <TargetFramework> value to your target .NET version. For example:

  <!-- Before -->
  <TargetFramework>netcoreapp3.1</TargetFramework>
  
  <!-- After -->
  <TargetFramework>net6.0</TargetFramework>
  

• Verify SDK installation
  Make sure you have the target .NET SDK installed locally. Run this command in your terminal to confirm:

  dotnet --version
  

• Check for deprecated/removed APIs
  Your IDE (like Visual Studio or Rider) will flag obsolete code, and running dotnet build will output warnings about APIs that have been removed or replaced. You’ll need to update these to use the new recommended alternatives.
• Test configuration and startup logic
  Some .NET versions tweak configuration loading order or service registration defaults (e.g., the move to top-level statements in .NET 6+ Program.cs). While old startup code will still work, you might want to refactor to take advantage of new features—but this is optional for basic functionality.

什么时候需要调整基础应用？ #

You’ll need to make targeted adjustments if:

• Your app uses APIs that were completely removed (not just deprecated) in the new .NET version. For example, certain ASP.NET Core middleware from older versions no longer exists and requires replacement.
• You rely on specific runtime behaviors that changed (e.g., GC settings, async stream handling, or authentication pipeline defaults). These might require small tweaks to maintain expected functionality.
• Your app has custom logic tied to old SDK tools (e.g., outdated MSBuild targets or publish profiles). These might need updates to work with the new SDK.

完全迁移到新应用的极端场景 #

Full migration to a new project is rarely necessary for .NET Core-to-.NET Core upgrades. You’d only consider this if:

• Your existing codebase is extremely messy, untested, or tightly coupled to outdated patterns that make incremental upgrades too error-prone.
• You’re using a very old .NET Core version (like 1.x) that’s drastically different from modern .NET, and the effort to fix all breaking changes outweighs rebuilding.

Final Takeaway #

Start with a direct upgrade: update your TFM, resolve any API deprecations, and run your test suite. Most apps will work with minimal tweaks. Only consider a full migration if you hit insurmountable issues that make incremental fixes impractical.

内容的提问来源于stack exchange，提问作者Pierre-luc Des.