C＃无法使用LINQ更新记录

Question

    public static bool CheckLogin(string Username, string Password, bool AutoLogin)
    {
        bool LoginSuccessful;

        // Trim inputs and verify lengths
        Username = Username.Trim();
        Password = Password.Trim().ToLower();

        // Get the associated user records
        DataClassesDataContext db = new DataClassesDataContext();
        var q = (from User in db.tblForumAuthors where User.Username == Username select new
                {
                    User.Password,
                    User.Salt,
                    User.Username,
                    User.Author_ID,
                    User.User_code,
                    User.Active,
                    User.Login_attempt,
                    User.Last_visit,
                }).SingleOrDefault();

        // Invalid details passed
        if (q == null)
        {
            LoginSuccessful = false;
        }
        else
        {
            // Increment login attempts counter
            int LoginAttempts = q.Login_attempt;
            LoginAttempts++;

            // Encrypt the password
            string HashedPassword = GetSha1(Password + q.Salt);

            // Check passwords match
            if (q.Password == HashedPassword)
            {
                LoginSuccessful = true;
            }
            else
            {
                LoginSuccessful = false;

                // Increment login attempts
                q.Login_attempt = LoginAttempts;
                db.SubmitChanges();
            }
        }
        return LoginSuccessful;
    }
}

On the line

q.Login_attempt = LoginAttempts;

I get:

Error 50 Property or indexer 'AnonymousType#1.Login_attempt' cannot be assigned to -- it is read only C:\\inetpub\\wwwroot\\ScirraNew\\App_Code\\Login.cs 82 17 C:\\...\\ScirraNew\\

Can anyone show me how I can update this counter in the record please?

Answer 1

You need to just select the whole User item if you want to edit it. Get rid of your whole "Select New" clause.

Answer 2

You can't update properties of an anonymous class instance (even if you could that change just would be local and not be related to any User entity in the DB since the anonymous class instance is a new and different object that you are projecting to), you have to select the User entity itself to update.

So instead of:

var q = (from User in db.tblForumAuthors
            where User.Username == Username
            select new
            {
                User.Password,
                User.Salt,
                User.Username,
                User.Author_ID,
                User.User_code,
                User.Active,
                User.Login_attempt,
                User.Last_visit,
            }).SingleOrDefault();

Use:

var q = (from User in db.tblForumAuthors where User.Username == Username select User).SingleOrDefault();

Or in lambda syntax:

var user =  db.tblForumAuthors.Where( u => u.UserName == UserName)
              .SingleOrDefault();