how to create dbcontext in entity framework core database first code example

Example 1: asp.net core entity framework database first

PM> Scaffold-DbContext "Server=.\SQLExpress;Database=SchoolDB;Trusted_Connection=True;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models

Example 2: generic dbcontext entity framework core

public class SampleContext : GuidDbContext
    {
        public IDbSet<Foo> Foos { get; set; }
        public IDbSet<Bar> Bars { get; set; }
    }