Want to protect your cyber security and still get fast solutions? Ask a secure question today.Go Premium

x
  • Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 415
  • Last Modified:

Record Locking

Please can someone explain the best way to stop duplicates in SQL Server 7.

I have a web page which via 2 recordsets finds the next id number + 1, then saves the record in the database through the second recordset doing rs.addnew.

I want to make sure there is no way even with two people pushing the buttons at the same time can create the same id.
0
andy_booth
Asked:
andy_booth
1 Solution
 
hongjunCommented:
Use transaction something like this.

objConn.BeginTrans
objCon.Execute("insert into your_table values (1)")
objConn.CommitTrans


hongjun
0
 
nigelroweCommented:
This is a tricky problem. It is almost impossible to guarantee no duplicates. The easiest way is to use a serial type field when adding new records. SQL server allots the number automatically. The problem is if you want to recuperate the alloted number immediately after the update. Another easy method (but again not foolproof) is to do a "SELECT MAX(idfield) FROM table" just before the insert. Add 1 to this value and do the INSERT. The safest way (in my opinion) is to use MTS shared property groups for this. Using these, with multi users accessing the same property value, the first to arrive takes the lead, the others are queued until the first releases the property, and so on and so forth, thus avoiding any DB concurrency locks on the table. This method, however, implies an ActiveX component. I don't know how complicated you want to go.

Hope this helps
0
 
andy_boothAuthor Commented:
Where do I fit that into my code. Posted below...

sql = "SELECT MAX(quote_reference) FROM quote"
   
   set conn = Server.CreateObject("ADODB.Connection")
   conn.Open session("ses_connection")
   set cmd = Server.CreateObject("ADODB.Command")
   cmd.CommandText = sql
   set cmd.ActiveConnection = conn
   set rs = Server.CreateObject("ADODB.Recordset")
   set rs = cmd.Execute
   
   session("ses_quote_reference") = rs.Fields(0).Value
   
   If isnull(session("ses_quote_reference")) Then
    session("ses_quote_reference") = 1
   Else
    session("ses_quote_reference") = session("ses_quote_reference") + 1
   End If
   
   sql_insert = "SELECT * FROM quote WHERE 1=0"
   
   set conn_insert = Server.CreateObject("ADODB.Connection")
   conn_insert.Open session("ses_connection")
   set cmd_insert = Server.CreateObject("ADODB.Command")
   cmd_insert.CommandText = sql_insert
   set cmd_insert.ActiveConnection = conn_insert
   set rs_insert = Server.CreateObject("ADODB.Recordset")
   rs_insert.Open sql_insert, conn_insert, 2, 3
   
   rs_insert.AddNew    
   rs_insert.Fields("quote_reference").Value = session("ses_quote_reference")
   rs_insert.Fields("quote_type").Value = "Truck"
   rs_insert.Fields("status").Value = "Incomplete"
   rs_insert.Fields("date_added").Value = date()
   rs_insert.fields("broker").value = session("ses_username")
   rs_insert.update
0
Concerto's Cloud Advisory Services

Want to avoid the missteps to gaining all the benefits of the cloud? Learn more about the different assessment options from our Cloud Advisory team.

 
hongjunCommented:
<%
  sql = "SELECT MAX(quote_reference) FROM quote"
 
  set conn = Server.CreateObject("ADODB.Connection")
  conn.Open session("ses_connection")
  set cmd = Server.CreateObject("ADODB.Command")
  cmd.CommandText = sql
  set cmd.ActiveConnection = conn
  set rs = Server.CreateObject("ADODB.Recordset")
  set rs = cmd.Execute
 
  session("ses_quote_reference") = rs.Fields(0).Value
 
  If isnull(session("ses_quote_reference")) Then
   session("ses_quote_reference") = 1
  Else
   session("ses_quote_reference") = session("ses_quote_reference") + 1
  End If
 
  sql_insert = "SELECT * FROM quote WHERE 1=0"
 
  set conn_insert = Server.CreateObject("ADODB.Connection")
  conn_insert.Open session("ses_connection")
  set cmd_insert = Server.CreateObject("ADODB.Command")
  cmd_insert.CommandText = sql_insert
  set cmd_insert.ActiveConnection = conn_insert
  set rs_insert = Server.CreateObject("ADODB.Recordset")

  conn.begintrans

  rs_insert.Open sql_insert, conn_insert, 2, 3
 
  rs_insert.AddNew    
  rs_insert.Fields("quote_reference").Value = session("ses_quote_reference")
  rs_insert.Fields("quote_type").Value = "Truck"
  rs_insert.Fields("status").Value = "Incomplete"
  rs_insert.Fields("date_added").Value = date()
  rs_insert.fields("broker").value = session("ses_username")
  rs_insert.update

  conn.committrans
%>


hongjun
0
 
hongjunCommented:
You might also need this

<%@Language=VBScript transaction=required%>

<%
Sub OnTransactionCommit()
' put anything you want here
End Sub

Sub OnTransactionAbort()
     Response.write ("<br><br><font color=red size=4>Transaction Failed! Please contact system adminstrator.</font>")
     Response.End
End Sub
%>


<%
 sql = "SELECT MAX(quote_reference) FROM quote"
 
 set conn = Server.CreateObject("ADODB.Connection")
 conn.Open session("ses_connection")
 set cmd = Server.CreateObject("ADODB.Command")
 cmd.CommandText = sql
 set cmd.ActiveConnection = conn
 set rs = Server.CreateObject("ADODB.Recordset")
 set rs = cmd.Execute
 
 session("ses_quote_reference") = rs.Fields(0).Value
 
 If isnull(session("ses_quote_reference")) Then
  session("ses_quote_reference") = 1
 Else
  session("ses_quote_reference") = session("ses_quote_reference") + 1
 End If
 
 sql_insert = "SELECT * FROM quote WHERE 1=0"
 
 set conn_insert = Server.CreateObject("ADODB.Connection")
 conn_insert.Open session("ses_connection")
 set cmd_insert = Server.CreateObject("ADODB.Command")
 cmd_insert.CommandText = sql_insert
 set cmd_insert.ActiveConnection = conn_insert
 set rs_insert = Server.CreateObject("ADODB.Recordset")

 conn.begintrans

 rs_insert.Open sql_insert, conn_insert, 2, 3
 
 rs_insert.AddNew    
 rs_insert.Fields("quote_reference").Value = session("ses_quote_reference")
 rs_insert.Fields("quote_type").Value = "Truck"
 rs_insert.Fields("status").Value = "Incomplete"
 rs_insert.Fields("date_added").Value = date()
 rs_insert.fields("broker").value = session("ses_username")
 rs_insert.update

 conn.committrans

' other stuff here
%>

hongjun
0
 
andy_boothAuthor Commented:
Hongjun,

I have added your code, (thanks for the help so far!)

However it runs your Sub OnTransactionAbort() everytime I try to add a record.

Here is the error!

Microsoft OLE DB Provider for SQL Server error '8004d013'

Cannot start more transactions on this session.

/croweonline_dev/home_quote.asp, line 174

Transaction Failed! Please contact system adminstrator.
0
 
makerpCommented:
wrap an

Application.Lock
 'your sensitive code
Application.Unlock

around the code in question, this will serialize access to to it, it is a heavy handed approach as it temporarily locks other users scripts. although it dont reallt matter if the script dont take long to execute
0
 
andy_boothAuthor Commented:
Had to play around a little bit. But got it to work.

Thanks very much.
0
 
OverSurgeCommented:
Andy.. I am getting this error with a SP that I am currently calling on a project I am working on. What did you end up changing to fix the "Cannot start more transactions on this session." ?
0
 
andy_boothAuthor Commented:
This was in ASP Oversurge.

MakerP's code worked for me.

Application.Lock
 'your sensitive code
Application.Unlock
0

Featured Post

What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

Tackle projects and never again get stuck behind a technical roadblock.
Join Now