How to resolve The type 'AssemblyCompanyAttribute' exists in both 'System.Runtime,' and 'netstandard'?

Question

I am experimenting with visual studio code, .net core 2.2 and entityframework all in one mix.

I do the following steps:

1) create new sln

dotnet new sln --name MySln

2) create a webapi:

dotnet new webapi --name api

3) create a class lib:

dotnet new classlib --name Api.DB

Add references to the projects:

dotnet sln "MyApi.sln" add "api/api.csproj"

dotnet sln "MyApi.sln" add "Api.DB/Api.DB.csproj"

dotnet add reference ../Api.DB/Api.DB.csproj

In the classlib I add the following:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
     <RuntimeFrameworkVersion>2.0.5</RuntimeFrameworkVersion>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="2.2.4"/>
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="2.2.4"/>
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="2.2.4"/>
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer.Design" Version="2.0.0-preview1-final"/> 
  </ItemGroup>
     <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.1" />
  </ItemGroup>
</Project>

Problem I dont understand this But i am getting the following error in the classlib:

The type 'AssemblyCompanyAttribute' exists in both 'System.Runtime, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' and 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51' (CS0433) [Api.DB]

EDIT:

forgot to mention that when comenting out all my packages in the classlib like so:

<!-- <PackageReference Include="Microsoft.EntityFrameworkCore" Version="*"/>
<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="*"/>
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="*"/>
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer.Design" Version="*"/> -->

Then the error dissapeares which confuses me even more? is there an error with the packages?

When I remove them and try to scafoled my db context then I get:

Startup project 'Api.DB.csproj' targets framework '.NETStandard'. There is no runtime associated with this framework, and projects targeting it cannot be executed directly. To use the Entity Framework Core .NET Command-line Tools with this project, add an executable project targeting .NET Core or .NET Framework that references this project, and set it as the startup project using --startup-project; or, update this project to cross-target .NET Core or .NET Framework. For more information on using the EF Core Tools with .NET Standard projects, see https://go.microsoft.com/fwlink/?linkid=2034781

Answer 1

I have been working on resolving my error for some time now and I finaly came to a solution.

After @Lesiak gave me the link in the comments I put the following into my classlib:

  <PropertyGroup>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
  </PropertyGroup> 
  <PropertyGroup>
    <EnableDefaultRazorTargetAssemblyInfoAttributes>false</EnableDefaultRazorTargetAssemblyInfoAttributes>
  </PropertyGroup> 

This resolved the original error.

However The guide i was following for this was for .net core 2.0 so I included the following in the classlib

<RuntimeFrameworkVersion>2.0.5</RuntimeFrameworkVersion> 

But I am targeting .netcore 2.2 so I had to change the targetframework to:

  <TargetFrameworks>netcoreapp2.2;netstandard2.0</TargetFrameworks>