C# REQUEST HANDLER ERROR System.InvalidCastException: Specified cast is not valid

Question

When i try to execute this function i get the error "System.InvalidCastException: Specified cast is not valid."

System.InvalidCastException: Specified cast is not valid.
   at server.mihail.credits.HandleRequest() in F:\Users\Mihail\Documents\new-sentients-2016\server\mihail\credits.cs:line 34
   at server.RequestHandler.HandleRequest(HttpListenerContext context) in F:\Users\Mihail\Documents\new-sentients-2016\server\RequestHandlers.cs:line 37
   at server.Program.ProcessRequest(HttpListenerContext context) in F:\Users\Mihail\Documents\new-sentients-2016\server\Program.cs:line 156

This is the function: I try to execute it with parameters guid as my email address and parameter aid with the number one in it.

Please help me, i have been trying all day to fix it.

class credits : RequestHandler
{
    protected override void HandleRequest()
    {
        string status = "403";
        using (Database db = new Database())
        {
        NameValueCollection query = HttpUtility.ParseQueryString(Context.Request.Url.Query);
        MySqlCommand cmd = db.CreateQuery();
        cmd.CommandText = "SELECT id FROM accounts WHERE uuid=@uuid";
        cmd.Parameters.AddWithValue("@uuid", query["guid"]);
        object id = cmd.ExecuteScalar();
        if (id != null)
        {
        int amount = int.Parse(query["aid"]);
        cmd = db.CreateQuery();
        cmd.CommandText = "UPDATE stats SET credits = credits + @amount WHERE accId=@accId";
                cmd.Parameters.AddWithValue("@accId", (int) id);
                cmd.Parameters.AddWithValue("@amount", amount);
                int result = cmd.ExecuteNonQuery();
                if (result > 0)
                    status = "400";
                else
                    status = "500";
           }
            else
               status = "404";
        }
        byte[] res = Encoding.UTF8.GetBytes(
             status);
        Context.Response.OutputStream.Write(res, 0, res.Length);
    }
}

Answer 1

Based on the limited information you have provided, it looks like the problem is with the line cmd.Parameters.AddWithValue("@accId", (int) id);, as that is the only line with a cast.

Check the type of the accounts.id column in your database, I suspect it is not an INT, so you will need to change the cast (the type in the parentheses) to whatever type it is. A SMALLINT is a short in C#, BIGINT is long, TINYINT is byte (or sbyte), and you'd need to look at the documentation to see what MEDIUMINT maps to, but its probably int.