C3rd

Few days ago, been learning again ASP.Net C#, but this time its ASP.Net Core C#. It took me a while to resolve this issue because all the reference in the internet and stackoverflow were for Visual Studio 2017.

DotNet Version: 3.1 | IDE: VS 2019

In VS2017 might work just by adding:

use using Microsoft.EntityFrameworkCore;

But in VS2019, what works is both adding describe above and execute add package:

dotnet add package Microsoft.EntityFrameworkCore.SqlServer

after that, you problem should go away...