How do I Validate a User Using LINQ to SQL?

Hi ,

I'm trying to work out how to validate a user in my application but i don't know how. I wish create a form with Username and Password to enter in the application(WPF) using Linq toSql to store and validate Username and password in the database but i don't know so much about Linq to Sql so i keep in stuck now. I have a database with this fields"UserID,UserTypeID,Name,Surname,Username,Password,Email" and here there is the code that i use :

public Window1()
    {
        InitializeComponent();

    }

    public bool ValidateApplicationUser(string userName, string password)
    {
        bool validUser = false;
        try
        {
         //   var conn = "Data Source=MAMMA-PC/SQLMAMMA;Initial Catalog=MyWebSite;Integrated Security=True";
            DataClasses1DataContext dc = new DataClasses1DataContext();
            Table<User> users = dc.GetTable<User>();

            var query = from c in dc.Users
                        where (c.Username == userName.ToLower() && c.Password == password.ToLower())
                        select c;

            validUser = (query != null);

        }
        catch (Exception ex)
        {
            if (ex != null)
            {
            }
        }

        return validUser;
    }

    private void mahhh(object sender, RoutedEventArgs e)
    {



        bool authenticated = true;
     //   var conn = "Data Source=MAMMA-PC/SQLMAMMA;Initial Catalog=MyWebSite;Integrated Security=True";
            DataClasses1DataContext dc = new DataClasses1DataContext();
            Table<User> users = dc.GetTable<User>();

            var query = from c in dc.Users
                        where (c.Username == usernameTextBox.Text.ToString() && c.Password == passwordTextBox.Text.ToString())
                        select c;

      /*      foreach (User user in query)
            {
                user.Username = usernameTextBox.Text.Trim();
                user.Password = passwordTextBox.Text.Trim();
            } */


        {
            if (usernameTextBox.Text !="" && passwordTextBox.Text != "")
            {
                authenticated = ValidateApplicationUser(usernameTextBox.Text , passwordTextBox.Text);
            }

        }
        if (!authenticated)
        {
            MessageBox.Show("Invalid login. Try again.");
        }
        else
        {
            MessageBox.Show("Congradulations! You're a valid user!");


    //        Window2 c = new Window2();
    //        c.ShowDialog();
            this.Close();
        }

    }

When i insert the password and username the form validate also wrong username and password so i receive always the message "Congradulations! You're a valid user!"!!!

DO you have any advice where i wrong?

Bye

From stackoverflow

• validUser = (query.Count() == 0);
  

  xcud : ... shortest accepted answer (with code) bait ...

  Drew Noakes : Instead of this you can use the faster: validUser = !query.Any();

  xcud : Well played, sir.

• Firstly its a best practice to Hash Passwords(one way encryption) with a Salt (random string you tag on the end of your password), I know it sounds complex but it isn't.

  It isn't a good practice to wrap everything around with try, unless you are

  The Linq Code Would Be

  public bool ValidateApplicationUser(string userName, string password)
  {
      //Get Database Context
      var AuthContext = new DataClasses1DataContext();
  
      //We Are Only Going To Select UserId, Notice The Password .ToLower Is Removed (for security)
      var query = from c in AuthContext.Users
                  where (c.Username == userName.ToLower() && c.Password == password)
                  select c;
  
      if (query.Count() != 0) {
         return true;
      }
  
      return false;
  }
  

  Salt Could Be Done Using Database Or C#

  http://blog.stevex.net/index.php/c-code-snippet-creating-an-md5-hash-string/

  JayJay : Hi ELijah ,that's all right ,i can authenticate with so well now...Thanks so much. let me ask you about HashPassword with a Salt do you have some example about that??? Have a lucky day. Bye