How do I force myProject Choose .NetStandard assembly instead of TargetFramework

[John0King]

Today , There are Asp.Net (System.Web.HttpContext) and Asp.Net Core (Microsoft.AspNetCore.Http.HttpContext) in .net Framework , and there are a few packages use .net Framwork with System.Web.HttpContext and .net Core (.net standard) with Microsoft.AspNetCore.Http.HttpContext for sharing source , so when I use Asp.Net Core on .Net Framework , I just can not use that package because that package fouce me to use System.Web.HttpContext , but there is an available assembly in that package, How do I choose that ?

[livarcocc]

Can you give us some more information here? What does your project look like? Could you share that? It will pick the appropriate API surface based on your Target Framework.

[John0King]

@livarcocc That's the problem.
for example I create a FooLib package with :

<TargetFramework>net45;netstandard2.0</TargetFramework>

<PackageReference Condition="'$(TargetFramework)' == 'NetStandard2.0'" Include="Microsoft.AspNetCore.Http" />
<Reference Condition="'$(TargetFramework)' != 'NetStandard'" Include="System.Web" />

and some code

#if NETSTANDARD20
var context  = IHttpContextAccessor.HttpContext;
#else
var context  = System.Web.HttpContext.Current;
#end if

var q = context.Request["q"];

if I use that lib in an Asp.NET Core application ( .NetFramework Runtime ) , The App will Choose Net4.5's version.

Is there any way to force my app to choose .net standard version ?

[livarcocc]

From the conditions you have in your project above, it seems like the Reference will always be added. Because you are checking against NetStandard alone.

[John0King]

@livarcocc I know it's bad, and I'll never use that pattern , but I can not controll other people to use that like this.
There are a few Nuget packages are packaged like this. (they try to make this package work both on Asp.net Core and traditional asp.net , but they forget the asp.net core can running on full .net framework too),

I hope something like this :
in my main app I can do

<TargetFramework>net461</TargetFramework>
...
<PackageReference Include="OneOfThePackage" Version="1.0.0" Choose="NetStandard2.0" />

Is there any attribute to do this ?

[livarcocc]

You can condition it with something like this:

  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
    <PackageReference Include="OneOfThePackage" Version="1.0.0" />
  </ItemGroup>

Is there a reason why something like this would not work for you? We use it like this our own projects.

[dasMulli]

they try to make this package work both on Asp.net Core and traditional asp.net , but they forget the asp.net core can running on full .net framework too

I've seen this before - assuming that netstandard* assets will be used on ASP.NET Core and net* assets on classic ASP.NET.

You correctly assume that this does not account for ASP.NET Core on .NET Framework.
It is a package authoring issue that needs to be resolved by the NuGet packages' authors who will need to publish a different package for ASP.NET Core in addition to the package for classic ASP.NET.

[John0King]

@dasMulli

It is a package authoring issue that needs to be resolved by the NuGet packages' authors who will need to publish a different package for ASP.NET Core in addition to the package for classic ASP.NET.

That's the right way, but there is an available assembly(.net standard assembly) in that package!!
if I don't use nuget , and menuly reference that .net standard dll , that works .

and there are other condition may need this: many nuget package target net45 and netstandard2.0 , and when you target net471 , which assembly will use ?

That's why I hope there is a choose attribute on PackageReference node

[dasMulli]

I do feel your pain using this. I don't work for microsoft or the .net foundation so I can only give hints to this.

apart from the asp.net core/classic selection, I have also seen issues with different public APIs in NuGet packages:
If a netstandard project uses a library, it will compile against netstandard assets. if a net* project (csproj) then references this project (csproj), it will use the project reference compiled against the netstandard assets but consume the package's net* assets. This even applies when the netstandard project is published as a NuGet package.

Are you having trouble using a public NuGet package? I could probably cook up custom hacky msbuild targets modifying your compile references as a last resort

[b-anand]

I have similar problem. I have a utilities project targeting .net standard which references a third party nuget. I have another exe project referencing the utilities project.

The third party nuget has both .net framework and .net standard dll in it but they have been compiled with different versions of Unity nuget (Unity made a breaking change across version 4 and 5 by changing the dll names). The .net framework version of the dll in third party nuget references version 4 of Unity (Microsoft.Practices.Unity.dll) and .net standard version of the dll in the third party nuget references version 5 of Unity (Unity.dll).

The utilities project in my code is targetting .net standard and references the aforementioned nuget so it compiles against the .net standard version of the dll.

The exe project which references the utilitites project above targets .net Fx and will pick the .net framework version of the dll from the nuget and place it next to the exe.

At runtime the utilities project fails saying the Unity class/method not found.

If there was a way to force the exe project to reference the .net standard version of the nuget then we would binplace the .net standard version of the dlls which would then just work.

[carlosrpg]

I Have the same problem here, I Have a net472 app that requires to be full framework, and I consume a nuget (netStandard2.0), this nuget have a reference for another nuget that provides both net45 and netstandard2.0.
Now I'm stuck at using the net45 version cause I can't control how the targetframework will be choosed. This would not be a problem using packages.config because I could just add a reference to this dependency and choose the targetframework for netstandard2.0 but now using PackageReference this is not possible.

This is definitely PackageReference bug or removed feature (that should have being disclaimed).

[fschmied]

Same problem here: We reference NUnit via PackageReference from a net47-csproj. The NUnit package contains net45 and netstandard1.6 libs. NuGet automatically resolves to net45, although netstandard1.6 would also be compatible.

We need to use the netstandard1.6 version because of a certain feature, but this doesn't seem possible at the moment.

[cortex93]

Same issue : NuGet/Home#7385