не могу установить [.net ядро] пакеты с помощью Visual Studio код (DotNet кли)


Я с использованием новейшей основного жереха 3.1 рамки. Пытаюсь настроить мои базы данных. но есть проблема. я не могу установить следующие пакеты

dotnet tool install --global dotnet-ef
dotnet tool install --global dotnet-aspnet-codegenerator
dotnet add package Microsoft.EntityFrameworkCore.SQLite
dotnet add package Microsoft.VisualStudio.Web.CodeGeneration.Design
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer

i get the following errors. will appreciate it if any one can help with 
a solution.

error NU1100: Unable to resolve 'dotnet-aspnet-codegenerator ' for '.NETCoreApp,Version=v3.1'.
error NU1100: Unable to resolve 'dotnet-aspnet-codegenerator ' for '.NETCoreApp,Version=v3.1/any'.
The tool package could not be restored.
Tool 'dotnet-aspnet-codegenerator' failed to install. This failure may have been caused by:

* You are attempting to install a preview release and did not use the --version option to specify the version.
* A package by this name was found, but it was not a .NET Core tool.
* The required NuGet feed cannot be accessed, perhaps because of an Internet connection problem.
* You mistyped the name of the tool.

Это происходит, когда я пытаюсь установить любого из пакетов.

Задан 13/01/2020 в 22:04
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