C# Winforms Npgsql 3.0.5 "An operation already in progress" error when trying to run multiple commands inside same connection

Question

I'm trying to run the following snippet in C# Winforms. This piece of code is working well with pgsql 2.2.6 adapter. What correction can be made in order to work fine with pgsql3.0.5 adapter? Thanks.

NpgsqlConnection conn = new NpgsqlConnection(MainForm2.MyConString);
        {
            conn.Open();
            using (NpgsqlCommand cmd = new NpgsqlCommand("SELECT rfid,name,sc_id from passenger ORDER by name", conn))
            {
                NpgsqlDataReader dr = cmd.ExecuteReader();
                while (dr.Read())
                {
                    var obj = new PassengerClass
                    {
                        RFID = dr.GetString(0),
                        Name = dr.GetString(1),
                        sc_id = dr.GetInt32(2)
                    };
                    s = dr.GetString(0);
                    try { ret.Add(s, obj); }
                    catch (Exception ex) { SM.Debug("Fail to add RFID Name in hash RFID:" + s + ex.ToString()); }
                }
            }
            MainForm2.PassHash = ret;
            try
            {
                using (NpgsqlCommand cmd = new NpgsqlCommand(string.Format("UPDATE place set useridx ={0} where useridx=0", MainForm2.userIDX), conn))
                    cmd.ExecuteNonQuery();

                using (NpgsqlCommand cmd = new NpgsqlCommand(string.Format("UPDATE zonename set useridx ={0} where useridx=0", MainForm2.userIDX), conn))
                    cmd.ExecuteNonQuery();
            }
            catch (Exception ex)
            {
                SM.Debug("Error on update users IDX for place and zone with value 0 :" + ex.ToString());
            }

So, at the second command statement it gives me the following error:

A first chance exception of type 'System.InvalidOperationException' occurred in Npgsql.dll

Additional information: An operation is already in progress.

EDIT Additional info:

Answer 1

You need to dispose of the NpgsqlDataReader which you get in the first ExecuteReader call: wrap it with a using statement just like you do with your NpgsqlCommand.

Disposing NpgsqlDataReader doesn't close the connection - only disposing the connection does that. An open reader corresponds to an open command currently running, which you must close before executing a new command. For atomicity, you can just start a transaction which encompasses several commands.