Check if user exists in MVC4 - asp.net-mvc

Question

I have simple login form without registration, because I create Admin login, who create new users. So admin login, and create new user, which can then login with that specific username and password.
So I create this controller:
public ActionResult CreateNew(Models.Users user)
{
if (ModelState.IsValid)
{
try
{
using (var dataU = new userDbEntities())
{
var crypto = new SimpleCrypto.PBKDF2();
var encrpPass = crypto.Compute(user.Password);
var sysUser = dataU.UsersTables.Create();
sysUser.username = user.Username;
sysUser.password = encrpPass;
sysUser.passwordSalt = crypto.Salt;
sysUser.TimeZoneId = user.TimeZoneName;
sysUser.Customer = user.Customer;
dataU.UsersTables.Add(sysUser);
dataU.SaveChanges();
return RedirectToAction("Registration", "LoginAdmin");
}
}
catch (Exception ex)
{
string error = ex.Message;
}
}
return View(user);
}
Problem is, that I can create users with same username (this is not ok!), so how to check if user with that name exists and returns, this username already exists...
thanks...

Answer 1

count the number of user that has the same username and add the user if the count is 0.
for example
var count = dataU.UsersTables.Count(u=>u.UserName == usernameyouwanttocheck);
if(count==0)
{
//add user
}
else
{
//alert user saying user exists
}
if I were you I would make repository and create a function that checks if the user exists or not and call that function from controller.

Answer 2

By help of Biplov13 I create this, which is working:
public ActionResult CreateNew(Models.Users user)
{
if (ModelState.IsValid)
{
try
{
using (var dataU = new userDbEntities())
{
{
var crypto = new SimpleCrypto.PBKDF2();
var encrpPass = crypto.Compute(user.Password);
var sysUser = dataU.UsersTables.Create();
sysUser.username = user.Username;
sysUser.password = encrpPass;
sysUser.passwordSalt = crypto.Salt;
sysUser.TimeZoneId = user.TimeZoneName;
sysUser.Customer = user.Customer;
var count = dataU.UsersTables.Count(u => u.username == user.Username);
if (count == 0)
{
dataU.UsersTables.Add(sysUser);
dataU.SaveChanges();
return RedirectToAction("Registracija", "LoginAdmin");
}
else
{
// something to do if user exist...
}
}
}
}
catch (Exception ex)
{
string error = ex.Message;
}
}
return View(user);
}