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C# oracle query - Lock, then update, then select

Posted on 2010-08-23
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Last Modified: 2012-05-10
I am trying to write a oracle query that will lock a table then update the value by one then select the value.

But how would i write this to activate?

Here is what i have so far:

StringBuilder ticketNumber = new StringBuilder();
                string oradb = "Data Source=whs01_d; User Id=emuuser; Password=";
                string sqlLock = "lock table helpq.qw_keys in exclusive mode ";
                string sqlUpdate = "update helpq.qw_keys set keyvalue=keyvalue+1 where tablename='calls' ";
                string sqlSelect = "select keyvalue "
                                    + "from helpq.qw_keys "
                                    + "where tablename='calls' ";

                OracleConnection conn = new OracleConnection();
                conn.ConnectionString = oradb;

                conn.Open();

                OracleCommand cmdLock = new OracleCommand(sqlLock, conn);
                OracleCommand cmdUpdate = new OracleCommand(sqlUpdate, conn);
                OracleCommand cmdSelect = new OracleCommand(sqlSelect, conn);

                OracleDataReader dr = cmdSelect.ExecuteReader();

                if (dr.HasRows == true)
                {

                    while (dr.Read())
                    {
                        ticketNumber.AppendFormat(dr["keyvalue"].ToString());
                    }

                    return (ticketNumber.ToString());
                }

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How do i get the lock to happen then the update? they aren't running.

God Bless!

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Question by:benandbecky
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16 Comments
 
LVL 76

Expert Comment

by:slightwv (䄆 Netminder)
Comment Utility
I don't see where you are executing the other commands.

something like: cmdLock.ExecuteNonQuery();

also, Why lock the entire table to update a few rows?  Typically in Oracle there's no need to do this but if you still insist, why not a select for update.
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Author Comment

by:benandbecky
Comment Utility
Can you show me the code how to do this?

Thanks!
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LVL 76

Expert Comment

by:slightwv (䄆 Netminder)
Comment Utility
code to do what?
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Author Comment

by:benandbecky
Comment Utility
select for an update
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LVL 76

Expert Comment

by:slightwv (䄆 Netminder)
Comment Utility
Just add 'FOR UPDATE' to the end of the select:

http://psoug.org/reference/select.html
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Author Comment

by:benandbecky
Comment Utility
hmm its still not working the execute no query didnt work either.

Any more ideas or examples?

Thanks!
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LVL 76

Expert Comment

by:slightwv (䄆 Netminder)
Comment Utility
you added 'for update' to the end of sqlSelect.

Execute the reader to make sure it executes and locks the rows.

Then you did something like:

...
                if (dr.HasRows == true)
                {

                    while (dr.Read())
                    {
                        ticketNumber.AppendFormat(dr["keyvalue"].ToString());
                        cmdUpdate.ExecuteNonQuery();
                    }
...
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Author Comment

by:benandbecky
Comment Utility
Its still not working, i don't know why not.
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LVL 76

Expert Comment

by:slightwv (䄆 Netminder)
Comment Utility
Can you post the complete code as it looks now?
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Author Comment

by:benandbecky
Comment Utility

StringBuilder ticketNumber = new StringBuilder();

                string oradb = "Data Source=whs01_d; User Id=emuuser; Password=emuuser1";

                string sqlLock = "lock table helpq.qw_keys in exclusive mode " ;

                string sqlUpdate = "update helpq.qw_keys "

                                        + "set keyvalue=keyvalue+1 "

                                        + "where tablename='calls' " ;

                string sqlSelect = "select keyvalue "

                                    + "from helpq.qw_keys "

                                    + "where tablename='calls' "

                                    + "for update " ;



                



                OracleConnection conn = new OracleConnection();

                conn.ConnectionString = oradb;



                conn.Open();



                OracleCommand cmdSelect = new OracleCommand(sqlSelect, conn);

                OracleCommand cmdUpdate = new OracleCommand(sqlUpdate, conn);





                OracleDataReader dr = cmdSelect.ExecuteReader();



                if (dr.HasRows == true)

                {



                    while (dr.Read())

                    {

                        //Class.Connection.CreateCommand(sqlLock, oradb);

                        ticketNumber.AppendFormat(dr["keyvalue"].ToString());

                        cmdUpdate.ExecuteNonQuery();

                    }



                    return (ticketNumber.ToString());

                }

                else

                {

                    ticketNumber.AppendFormat("<FONT COLOR='#FF0000'>Error Creating Ticket Number</FONT></b>");



                    return (ticketNumber.ToString());

                }

            }

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Author Comment

by:benandbecky
Comment Utility
It just stays processing forever
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Accepted Solution

by:
slightwv (䄆 Netminder) earned 500 total points
Comment Utility
I created a small test case.  It uses Oracle's ODP.Net not the MSoft provider.  It was tested and works using Oracle 10.2.0.3.

Every execution increments the value by 1.

Given the following table:
--------------------------------
drop table tab1 purge;
create table tab1( tablename varchar2(10), keyvalue number );

insert into  tab1 values('calls',0);
commit;

using System;

using System.Data;



using Oracle.DataAccess.Client;

using Oracle.DataAccess.Types;



public class Bob

{



	public static void Main(string[] args)

	{



			OracleConnection con = new OracleConnection();

			OracleDataReader dr;



			con = new OracleConnection("User Id=bud;Password=bud;Data Source=bud");



			OracleCommand sqlSelect = new OracleCommand();

			OracleCommand sqlUpdate = new OracleCommand();



			sqlSelect.CommandText = " select keyvalue from tab1 where tablename='calls' for update ";

			sqlUpdate.CommandText = " update tab1 set keyvalue = keyvalue+1 where tablename='calls' ";





			sqlSelect.Connection = con;

			sqlUpdate.Connection = con;



			con.Open();



        	dr = sqlSelect.ExecuteReader();

        	if(dr.Read()) {

        		sqlUpdate.ExecuteNonQuery();

        	}



			con.Close();

			con.Dispose();



	}



}

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LVL 76

Expert Comment

by:slightwv (䄆 Netminder)
Comment Utility
Are you just wanting to generate an incrementing number?  

If there can be gaps,  check out Oracle Sequences.  This is what they are for.

>>It just stays processing forever

I'm wondering if one of your previous attempts still has the row locked and the current run is waiting for it to be released...

I'm also not sure why you why you have the WHILE loop on the data reader.  Can the select statement ever return more than 1 row?
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Author Comment

by:benandbecky
Comment Utility
How would i parse that value out?

i tried this code:

dr = sqlSelect.ExecuteReader();

                if (dr.Read())

                {

                    sqlUpdate.ExecuteNonQuery();

                }



                ticketNumber2 = int.Parse(dr["keyvalue"].ToString());

                

			    con.Close();

			    con.Dispose();                    

                return (ticketNumber2);

                

            }

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LVL 76

Expert Comment

by:slightwv (䄆 Netminder)
Comment Utility
I'm not at work anymore so I can't provide working code but for a datareader is something like:

ticketNumber2 = dr.GetDecimal(0);
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Author Closing Comment

by:benandbecky
Comment Utility
Fast and responsive!
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