Solved

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

Posted on 2010-08-23
16
1,042 Views
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());
                }

Open in new window


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

God Bless!

0
Comment
Question by:benandbecky
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 8
  • 8
16 Comments
 
LVL 77

Expert Comment

by:slightwv (䄆 Netminder)
ID: 33503942
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.
0
 

Author Comment

by:benandbecky
ID: 33504085
Can you show me the code how to do this?

Thanks!
0
 
LVL 77

Expert Comment

by:slightwv (䄆 Netminder)
ID: 33504095
code to do what?
0
Creating Instructional Tutorials  

For Any Use & On Any Platform

Contextual Guidance at the moment of need helps your employees/users adopt software o& achieve even the most complex tasks instantly. Boost knowledge retention, software adoption & employee engagement with easy solution.

 

Author Comment

by:benandbecky
ID: 33504108
select for an update
0
 
LVL 77

Expert Comment

by:slightwv (䄆 Netminder)
ID: 33504204
Just add 'FOR UPDATE' to the end of the select:

http://psoug.org/reference/select.html
0
 

Author Comment

by:benandbecky
ID: 33504432
hmm its still not working the execute no query didnt work either.

Any more ideas or examples?

Thanks!
0
 
LVL 77

Expert Comment

by:slightwv (䄆 Netminder)
ID: 33504483
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();
                    }
...
0
 

Author Comment

by:benandbecky
ID: 33504858
Its still not working, i don't know why not.
0
 
LVL 77

Expert Comment

by:slightwv (䄆 Netminder)
ID: 33504884
Can you post the complete code as it looks now?
0
 

Author Comment

by:benandbecky
ID: 33504976

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());
                }
            }

Open in new window

0
 

Author Comment

by:benandbecky
ID: 33504984
It just stays processing forever
0
 
LVL 77

Accepted Solution

by:
slightwv (䄆 Netminder) earned 500 total points
ID: 33504991
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();

	}

}

Open in new window

0
 
LVL 77

Expert Comment

by:slightwv (䄆 Netminder)
ID: 33505049
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?
0
 

Author Comment

by:benandbecky
ID: 33505319
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);
                
            }

Open in new window

0
 
LVL 77

Expert Comment

by:slightwv (䄆 Netminder)
ID: 33505741
I'm not at work anymore so I can't provide working code but for a datareader is something like:

ticketNumber2 = dr.GetDecimal(0);
0
 

Author Closing Comment

by:benandbecky
ID: 33510709
Fast and responsive!
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This post first appeared at Oracleinaction  (http://oracleinaction.com/undo-and-redo-in-oracle/)by Anju Garg (Myself). I  will demonstrate that undo for DML’s is stored both in undo tablespace and online redo logs. Then, we will analyze the reaso…
Using SQL Scripts we can save all the SQL queries as files that we use very frequently on our database later point of time. This is one of the feature present under SQL Workshop in Oracle Application Express.
This video shows how to Export data from an Oracle database using the Original Export Utility.  The corresponding Import utility, which works the same way is referenced, but not demonstrated.
This video shows how to configure and send email from and Oracle database using both UTL_SMTP and UTL_MAIL, as well as comparing UTL_SMTP to a manual SMTP conversation with a mail server.

733 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question