Question

Could anyone notice what could be wrong with the following function:

public string Login(string username, string password)     {         string result = '';         string select = 'SELECT user_id FROM [user] WHERE username = @username AND password = @password';         SqlConnection conn = new SqlConnection(connectionString);         SqlCommand cmd = new SqlCommand(select, conn);         cmd.Parameters.AddWithValue('username', username);         cmd.Parameters.AddWithValue('password', password);         int userID = 0;         try         {             conn.Open();             userID = (int)cmd.ExecuteScalar();             if(userID > 0)             {                 result = addSession(userID);             }         }         catch(Exception ex)         {             string sDummy = ex.ToString();         }         return result;     } 

Don’t know why the line `userID = (int)cmd.ExecuteScalar(); throws an exception.

Thanks

Answer 1

Most likely there is no row in the table with that user/password. The docs for ExecuteScalar say that it returns null if the result set is empty, and you can’t cast null to int.