HOWTO: Wrap Remote Views into One SQL Transaction

• Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b, 5.0, 5.0a

SUMMARY

You can wrap multiple remote views into one transaction, which allows you to commit or rollback all changes to the back-end data tables in one step. For example, a bank transfer between a savings account and a checking account. If the subtraction from the savings account fails because of insufficient funds, you do not want the addition to the checking account to be completed. Thus, you can rollback the entire bank transaction.

MORE INFORMATION

In order to wrap the views into a transaction you must use Shared Connections and set the Transaction property of SQLSetProp to Manual (2).

When these two settings are set, SQLCommit() or SQLRollback() may be used to commit or rollback the transactions. The following steps show how to wrap two separate remote views in a transaction.

Step-by-Step Example

1. Create a connection to your back end data and name it Myconnection.



2. Create two updateable remote views named Myview1 and Myview2.



3. Make the views share the connection by modifying the remote view. From the Query menu choose Advanced Options. This displays a dialog box that contains the Shared Connection check box. Select the check box and click OK.



4. In the Command window or in code issue the following commands:

   
         USE Myview1
         USE Myview2 in 0
         m.Handle = CursorGetProp('ConnectHandle','Myview1')
         =SQLSETPROP(m.Handle,'Transaction',2) 

   This code gets the connection handle from the cursor and sets the Transaction property to two (2), which is manual mode. This mode allows you to use the SQLCOMMIT or SQLROLLBACK functions.



5. Modify some data in the views and issue the following code:

   
         =Tableupdate(1,.t.,'Myview1')
         =Tableupdate(1,.t.,'Myview2')
         =SQLCommit(m.Handle)
         =Requery('Myview1')
         =Requery('Myview2') 

   You can replace the SQLCommit with SQLRollback and see the data go back to its original value.

REFERENCES

For more information on creating connections:

Visual FoxPro Developer's Guide, Chapter 8, "Defining a Connection"; "Creating Views"

Visual FoxPro Online Help; search on "View Designer"; topic: "Update Tab"

Additional query words: kbDSupport kbDSE kbnokeyword

Keywords :
Version : WINDOWS:3.0,3.0b,5.0,5.0a
Platform : WINDOWS
Issue type : kbhowto