Entity Framework Core: DbContextOptionsBuilder does not contain a definition for 'usesqlserver' and no extension method 'usesqlserver'

First we install the Microsoft.EntityFrameworkCore.SqlServer NuGet Package:

PM > Install-Package Microsoft.EntityFrameworkCore.SqlServer

Then, after importing the namespace with

using Microsoft.EntityFrameworkCore;

we add the database context:

services.AddDbContext<AspDbContext>(options =>
    options.UseSqlServer(config.GetConnectionString("optimumDB")));

adding using Microsoft.EntityFrameworkCore;

manually solved the problem for me

Found that here

Edit...

for dotnet core 3.1 add

Microsoft.EntityFrameworkCore.SqlServer

Install below NuGet Package will solve your issue

Microsoft.EntityFrameworkCore.SqlServer

Install-Package Microsoft.EntityFrameworkCore.SqlServer

Follow the steps below.

Install Entity Framework Core Design and SQL Server database provider for Entity Framework Core:

dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer

Import Entity Framework Core:

using Microsoft.EntityFrameworkCore;

And configure your DbContext:

var connectionString = Configuration.GetConnectionString("myDb");
services.AddDbContext<MyDbContext>(options => 
    options.UseSqlServer(connectionString)
);

This is a known issue in the project system. See dotnet/project-system#1741