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Return Multiple Columns on MySQL Queries

Posted on 2008-06-25
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Last Modified: 2010-04-21
I have a MySQL Connection that works, but I can only 1 column per query. Here is my Connection Class:

    class clsMySqlODBCConnection
    {
        public int QueryType = 0;
        public System.Data.Odbc.OdbcConnection OdbcCon;
        public System.Data.Odbc.OdbcCommand OdbcCom;
        public System.Data.Odbc.OdbcDataReader OdbcDR;
        public string ConStr;
        private string MySqlServer = "linux02", MySqlPort = "", MySqlDatabase = "EbtronSystems", MySqlUser = "ebtron", MySqlUserPass = "ebtron", MySqlOption = "3";

        public clsMySqlODBCConnection()
        {
            ConStr = "DRIVER={MySQL ODBC 3.51 Driver};SERVER=" + MySqlServer + ";PORT=" + MySqlPort + ";DATABASE=" + MySqlDatabase + ";UID=" + MySqlUser + ";PWD=" + MySqlUserPass + ";OPTION=" + MySqlOption + "";
            OdbcCon = new System.Data.Odbc.OdbcConnection(ConStr);
           
            try
            {
                //txtLog.AppendText("Openning connection...\r\n");
                if (OdbcCon.State == ConnectionState.Closed)
                {
                    OdbcCon.Open();
                }
                //txtLog.AppendText("Connection opened\r\n");
                //MessageBox.Show("Connection opened\r\n");
            }
            catch (System.Data.Odbc.OdbcException Ex)
            {
                //txtLog.AppendText(Ex.Message + "\r\n");
                //MessageBox.Show("Could not access the database.\r\nPlease make sure you completed the fields with the correct information and try again.\r\n\r\nMore details:\r\n" + Ex.Message, "Database connection error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
        public void MySqlDisconnection()
        {
            if (OdbcCon.State == ConnectionState.Open)
            {
                OdbcCon.Close();
                //MessageBox.Show("Connected Closed\r\n");
            }
        }

        public string[] MySQLQuery(string qry, int fldidx)
        {
            List<string> list = new List<string>();

            string tStr = null;     // the following is not needed: = Convert.ToString(null);
            if (OdbcCon.State == ConnectionState.Open)
            {
                OdbcCom = new System.Data.Odbc.OdbcCommand(qry, OdbcCon);
                if (fldidx >= 0)
                {
                    OdbcDR = OdbcCom.ExecuteReader();
                    while (OdbcDR.Read())
                    {
                        tStr = Convert.ToString(OdbcDR[fldidx]);
                        list.Add(tStr);
                    }
                }
                else
                {
                    OdbcCom.ExecuteNonQuery();
                    QueryType = 1;
                }
            }
            return list.ToArray();
        }
        public void MySQLNONQuery(string qry)
        {
            if (OdbcCon.State == ConnectionState.Open)
            {
                OdbcCom = new System.Data.Odbc.OdbcCommand(qry, OdbcCon);
                OdbcCom.ExecuteNonQuery();
                QueryType = 1;
            }
        }

        public object InitializeCnnObject()
        {
            // Create and initilize a recordset to represent the User Table
            clsMySqlODBCConnection OpenConnection = new clsMySqlODBCConnection();
            return OpenConnection;
        }
    }
////////////////////


I run a query like this:

string[] strQryResults = null;

strQryResults = OpenConnection.MySQLQuery("SELECT * FROM AdvantageOrderForm WHERE ItemIndexNumber = '" + tmpItemIndexNumber + "'", 0);

I can return only one column I have to run another query in order to get another column:

strQryResults = OpenConnection.MySQLQuery("SELECT * FROM AdvantageOrderForm WHERE ItemIndexNumber = '" + tmpItemIndexNumber + "'", 1);

I have a table with more than 50 columns, it takes nearly a minute to run all those queries. I need to be able to run 1 query and be able to get results for all the columns.

I know this is all because of my function:
public string[] MySQLQuery(string qry, int fldidx)

But I'm pretty new to DotNet and also to C#, so I'm not sure how to make it work.

Thanks for any help
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Question by:SaltyDawg
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Expert Comment

by:jcoehoorn
Comment Utility
You can only get one column because the clsMySqlODBCConnection class _that you wrote_ (.Net style guildelines recommend against prefixes like 'cls', by the way) only returns one column.  If you want more, make your data wrapper class return more.  All the columns are there in the data reader.
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by:SaltyDawg
Comment Utility
Wow, the prefix "cls" is not good. Never knew that. What would having the prefix do to hurt me?

How do I get the other columns from the data reader? Changes would I have to do to the wrapper
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Accepted Solution

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jcoehoorn earned 500 total points
Comment Utility
"cls" won't really hurt anything.  It's just no longer a recommended best practice:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpgenref/html/cpconNETFrameworkDesignGuidelines.asp

As for fixing your wrapper, I'd just return the raw data reader, perhaps using a provider agnostic IDataReader to make it more flexible to database changes.  As it is, you are almost guaranteed to have to iterate through every result set you get at least three times:  Once to add the items to your list, once again internally when the list is converted to an array, and finally when the calling code actually uses the array.  Returning the raw datareader means you only have to iterate through the results once.
public IDataReader MySQLQuery(string qry)

{

    if (OdbcCon.State == ConnectionState.Open)

    {

        OdbcCom = new System.Data.Odbc.OdbcCommand(qry, OdbcCon);

        OdbcDR = OdbcCom.ExecuteReader();

    }

    return OdbcDR;

}

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Author Comment

by:SaltyDawg
Comment Utility
I'm trying to return the results using the function presented.

///////////////////////////////////////////////////////////////
            clsMySqlODBCConnection MySQLConn = new clsMySqlODBCConnection();
            IDataReader qryResults = null;

            qryResults = MySQLConn.MySQLQuery("SELECT * FROM `MainIndex` WHERE `SerialNumber` =110477");

            qryResults["ItemIndexNumber"];
///////////////////////////////////////////////////////////////
Am I getting so far. Or what do I have wrong?
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Expert Comment

by:jcoehoorn
Comment Utility
You have to read from your datareader before referencing any columns.
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Author Comment

by:SaltyDawg
Comment Utility
I'm sorry I'm still not getting this right. By the way I was studying this and found SqlDataReader, whats the difference? Some say SqlDataReader runs faster...
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Author Comment

by:SaltyDawg
Comment Utility
Am I anywhere close here:

            clsMySqlODBCConnection MySQLConn = new clsMySqlODBCConnection();

            MySQLConn.MySQLQuery("SELECT * FROM `MainIndex` WHERE `SerialNumber` =110477");

            MySQLConn.OdbcDR[0];

I'm sure MySQLConn.OdbcDR[0]; is wrong, just don't know where to go from there
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Author Comment

by:SaltyDawg
Comment Utility
Oh Think I have it now, this seems to work:

            string tStr1,tStr2 = null;
            string tResults = null;

            MySQLConn.MySQLQuery("SELECT * FROM `MainIndex` WHERE `SerialNumber` =110477");

            while (MySQLConn.OdbcDR.Read())
            {
                tStr1 = Convert.ToString(MySQLConn.OdbcDR["ItemIndexNumber"]);
                tStr2 = Convert.ToString(MySQLConn.OdbcDR["SerialNumber"]);
                MessageBox.Show(tStr1 + " - " + tStr2);
            }

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Expert Comment

by:jcoehoorn
Comment Utility
Odbc is generally slower than a native provider.  However, SqlDataReader is for SQL Server only.  For MySQL I would install the MySQL provider, Connector/Net:
http://www.mysql.com/products/connector/net/

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Author Closing Comment

by:SaltyDawg
Comment Utility
Thanks alot
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