C# Fatal error encoutered during data read

Question

I'm selecting about 20,000 records from the database and then I update them one by one.
I looked for this error and I saw that setting the CommandTimeout will help, but not in my case.

        public void Initialize()
    {
        MySqlConnectionStringBuilder SQLConnect = new MySqlConnectionStringBuilder();
        SQLConnect.Server = SQLServer;
        SQLConnect.UserID = SQLUser;
        SQLConnect.Password = SQLPassword;
        SQLConnect.Database = SQLDatabase;
        SQLConnect.Port = SQLPort;
        SQLConnection = new MySqlConnection(SQLConnect.ToString());
    }

        public MySqlDataReader SQL_Query(string query)
    {
        MySqlCommand sql_command;
        sql_command = SQLConnection.CreateCommand();
        sql_command.CommandTimeout = int.MaxValue;
        sql_command.CommandText = query;
        MySqlDataReader query_result = sql_command.ExecuteReader();
        return query_result;
    }

        public void SQL_NonQuery(string query)
    {
        MySqlCommand sql_command;
        sql_command = SQLConnection.CreateCommand();
        sql_command.CommandTimeout = int.MaxValue;
        sql_command.CommandText = query;
        sql_command.ExecuteNonQuery();
    }

And here is my method which makes the select query:

        public void CleanRecords()
    {
        SQLActions.Initialize();
        SQLActions.SQL_Open();
        MySqlDataReader cashData = SQLActions.SQL_Query("SELECT `cash`.`id`, SUM(`cash`.`income_money`) AS `income_money`, `cash_data`.`total` FROM `cash_data` JOIN `cash` ON `cash`.`cash_data_id` = `cash_data`.`id` WHERE `user`='0' AND `cash_data`.`paymentterm_id`='0' OR `cash_data`.`paymentterm_id`='1' GROUP BY `cash_data_id`");
        while(cashData.Read()){
            if(cashData["income_money"].ToString() == cashData["total"].ToString()){
                UpdateRecords(cashData["id"].ToString());
            }
        }
        SQLActions.SQL_Close();
    }

And here is the method which makes the update:

        public void UpdateRecords(string rowID)
    {
        SQLActions.Initialize();
        SQLActions.SQL_Open();
        SQLActions.SQL_NonQuery("UPDATE `cash_data` SET `end_date`='" + GetMeDate() + "', `user`='1' WHERE `id`='" + rowID + "'");
        SQLActions.SQL_Close();
    }

Changing the database structure is not an option for me.
I thought that setting the timeout to the maxvalue of int will solve my problem, but is looks like this wont work in my case. Any ideas? :)

EDIT: The error which I get is "Fatal error encoutered during data read".

UPDATE:

        public void CleanRecords()
    {
        StringBuilder dataForUpdate = new StringBuilder();
        string delimiter = "";

        SQLActions.Initialize();
        SQLActions.SQL_Open();
        MySqlDataReader cashData = SQLActions.SQL_Query("SELECT `cash`.`id`, SUM(`cash`.`income_money`) AS `income_money`, `cash_data`.`total` FROM `cash_data` JOIN `cash` ON `cash`.`cash_data_id` = `cash_data`.`id` WHERE `user`='0' AND `cash_data`.`paymentterm_id`='0' OR `cash_data`.`paymentterm_id`='1' GROUP BY `cash_data_id`");
        while (cashData.Read())
        {
            if (cashData["income_money"].ToString() == cashData["total"].ToString())
            {
                dataForUpdate.Append(delimiter);
                dataForUpdate.Append("'" + cashData["id"].ToString() + "'");
                delimiter = ",";
            }
        }
        SQLActions.SQL_Close();
        UpdateRecords(dataForUpdate.ToString());
    }

    public void UpdateRecords(string rowID)
    {
        SQLActions.Initialize();
        SQLActions.SQL_Open();
        SQLActions.SQL_NonQuery("UPDATE `cash_data` SET `end_date`='" + GetMeDate() + "', `user`='1' WHERE `id` IN (" + rowID + ")");
        SQLActions.SQL_Close();
    }

Answer 1

You may be able to use

UPDATE cash_data .... WHERE id IN (SELECT ....)

and do everything in one go. Otherwise, you could do it in two steps: first the select collects all the ids, close the connection and then do the update in obne go with all the ids. The code for the second option might look something like this:

    public void CleanRecords()
    {
        StringBuilder builder = new StringBuilder();
        string delimiter = "";

        SQLActions.Initialize();
        SQLActions.SQL_Open();
        MySqlDataReader cashData = SQLActions.SQL_Query("SELECT `cash`.`id`, SUM(`cash`.`income_money`) AS `income_money`, `cash_data`.`total` FROM `cash_data` JOIN `cash` ON `cash`.`cash_data_id` = `cash_data`.`id` WHERE `user`='0' AND `cash_data`.`paymentterm_id`='0' OR `cash_data`.`paymentterm_id`='1' GROUP BY `cash_data_id`");
        while(cashData.Read()){
            if(cashData["income_money"].ToString() == cashData["total"].ToString()){
                builder.Append(delimiter);
                builder.Append("'" + cashData["id"].ToString() + "'");
                delimiter = ",";       
            }
        }
        SQLActions.SQL_Close();

        UpdateRecords(builder.ToString());  


    }

public void UpdateRecords(string rowIDs)
{
    SQLActions.Initialize();
    SQLActions.SQL_Open();
    SQLActions.SQL_NonQuery("UPDATE `cash_data` SET `end_date`='" + GetMeDate() + "', `user`='1' WHERE `id` IN (" + rowIDs + ")";
    SQLActions.SQL_Close();
}

Answer 2

There are multiple problem:

First: You have reading information around 20K using data reader and then doing update one by one in reader itself. Reader holds the connection open until you are finished. So this is not the good way to do it. Solution: We can read the information using Data Adapter.

Second: Rather than doing one by one update, we can update in bulk in one go. There are multiple option for bulk operation. In SQL u can do either by sending information in XML format or u can use Table Valued Parameter (TVP) (http://www.codeproject.com/Articles/22205/ADO-NET-and-OPENXML-to-Perform-Bulk-Database-Opera) OR (http://dev.mysql.com/doc/refman/5.5/en/load-xml.html)