prevent multiple login using mvc-4

Question

i have two table name Register and Login,

when user logs in the, user id and its status=1 will be store in Logins table and when user logs out status will become 0.

my problem is how should i check at login time that user is already logged in or not,

any if conditions to check, below is my code

 

 

 

 public ActionResult GetLogin(Register d, Login r)

{

using (simpleEntities _LoginEntities = new simpleEntities())

{

var user = _LoginEntities.Registers.Where(u => u.Email.Equals(d.Email) && u.Password.Equals(d.Password)).FirstOrDefault();

string message = "User already logged in";

if (user != null)

{

List ddd = new List();

ddd = (from a in db.Logins where a.LogID == user.ID where (a.Status == (false)) select a).ToList();

if (ddd!=null)

{

Session["ID"] = user.ID.ToString();

Session["Email"] = user.Email.ToString();

Session["Username"] = user.Fname.ToString() + "" + user.Lname.ToString();

return RedirectToAction("UserDashBoard");

}

else

{

return Json(message, JsonRequestBehavior.AllowGet);

}

}

return View();

}

}