You should try to complete entities like teams for your player entity. Especially foreign keys.
[HttpPost]
public ActionResult Create(Player model)
{
if (ModelState.IsValid)
{
using (var db = new EfDb())
{
//Since you have the username cached, you can check the local EF cache for the object before hitting the db.
//var userProfile = db.UserProfiles.Single(u => u.UserName == User.Identity.Name);
var userProfile = db.UserProfiles.Local.SingleOrDefault(u => u.UserName == User.Identity.Name)
?? db.UserProfiles.SingleOrDefault(u => u.UserName == User.Identity.Name);
if (userProfile != null)
{
var player = new Player
{
UserProfile = userProfile,
....
....
};
player.TeamId = 5;
db.Players.Add(player);
db.SaveChanges();
}
}
}
PopulateTeamsDropDownList(model.TeamId);
return View(model);
}
And make sure the Dropdown from your view is Required and send correct value to the post method.