public class MyController : Controller
{
    private Models db;

    public ActionResult Index()
    {
        db = new Models();
        var foo = (from f in db.foo select f).ToList();
        return View(foo);
    }
}

public class MyController : Controller
{
    private readonly Models db = new Models();

    public ActionResult Index()
    {
        var foo = (from f in db.foo select f).ToList();
        return View(foo);
    }
}

public class MyController : Controller{
    public ActionResult Index()
    {
        using (var db = new Models())
        {
            var foo = db.Foo.ToList();
            return View(foo);
        }
    }
}

public class MyController : Controller
{
    public ActionResult Index()
    {
        using (Models db = new Models())
        {
            var foo = (from f in db.foo select f).ToList();
            return View(foo);
        }
    }
}