How do I use ASP.NET Core 3.0 types from a library project for shared Controllers, Middleware etc?

Question

While ASP.NET Core up to 2.2 could be consumed through NuGet to create library projects for shared Controllers, Middleware etc, how do I create a library that is able to use ASP.NET Core 3.0 types?

While for projects containing views there is a "Razor Class Library" (razorclasslib) template, how do I create a library that only contains logic components?

Martin Ullrich · Accepted Answer · 2019-09-03 09:16:49Z

40

Applications built for .NET Core 3.0 can reference one or more shared frameworks. ASP.NET Core is one of these shared frameworks (others would be the base .NET Core Shared framework and the Windows Desktop Shared Framework containing WinForms and WPF).

To reference ASP.NET Core from a classic .NET Core library targeting .NET Core 3.0 (netcoreapp3.0, not .NET Standard), you can use a FrameworkReference in the csproj to reference the framework:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netcoreapp3.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <FrameworkReference Include="Microsoft.AspNetCore.App" />
  </ItemGroup>

</Project>

When opened in Visual Studio, this additional framework reference will show up in the dependencies node in solution explorer:

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edited Sep 3, 2019 at 9:16

answered Sep 2, 2019 at 16:41

Martin Ullrich

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3 Comments

Rick Strahl Over a year ago

Yes that works and what's cool about this is that if you add it and only reference one or two things out of it you can build a trimmed EXE/Package and it'll pick out only what's needed, unlike explicit assembly refs. I needed IWebHostEnvironment only and the added footprint is tiny. Thanks!

user2163043 Over a year ago

and what if the library targets .net standard 2.1?

Martin Ullrich Over a year ago

Then you cannot use asp.net core APIs and need to retarget to netcoreapp3.0. Only EF Core and Microsoft.Extensions packages of the 3.0 releases can be used in .NET Standard.

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