DataContext.cs

public class DataContext : DbContext
    {
        public DataContext(DbContextOptions<DataContext> options)
            : base(options)
        {
        }

        public DbSet<Users> User { get; set; }
        public DbSet<Customers> Customer { get; set; }

        public class Users
        {
            public string Username { get; set; }
            public string Password { get; set; }
        }
        
        public class Customers
        {
            public string Name { get; set; }
            public string PhoneNumber { get; set; }
            public string Email { get; set; }
        }

    }

MainController.cs

public class MainController : Controller
    {
        private DataContext _context;

        public MainController(DataContext context)
        {
            _context = context;
        }
        
        public IActionResult MainPage(string username)
        {
            var query = (from u in _context.User
                         where u != null
                         select u).ToList();

            ViewData["DisplayUsername"] = query;

            return View();
        }
        
        }

web.config

  <connectionStrings>
    <add name="DataContext"
    providerName="System.Data.EntityClient"
    connectionString="Data Source=[SERVER-NAME];Initial Catalog=[DATABASE-NAME];Integrated Security=True;MultipleActiveResultSets=True;user id=[USERNAME];password=[PASSWORD];"/>
  </connectionStrings>