string connectionstring = "Server=(localdb)\mssqllocaldb;Database=aspnet-WebApplication1-pouet;Trusted_Connection=True;MultipleActiveResultSets=true";
var sqlOptions = new DbContextOptionsBuilder<ApplicationDbContext>()
.UseSqlServer(connectionstring)
.Options;

using (ApplicationDbContext context = new ApplicationDbContext(sqlOptions))
{
// do sth
}