BEGIN TRANSACTION Command
Begins a transaction. Transactions are supported only for tables in a database. See CREATE DATABASE and ADD TABLE for information on how to create and add tables to a database.
BEGIN TRANSACTION
Remarks
To save any modifications you made and end the transaction, issue END TRANSACTION. If the transaction fails (the server fails, the workstation fails, or you exit Visual FoxPro without committing the transaction) or if you issue ROLLBACK, the file or files in the transaction are restored to their original state.
Transactions can be nested five levels deep. An error is generated if you attempt a sixth level of nesting.
When you modify records in a table that is part of a transaction, other users on the network do not have access (read or write) to the records until you end the transaction.
When other users on the network try to access records you have modified, they must wait until you end your transaction. They receive the message "Record not available ... please wait" until the records become available. Because of this, it is important to keep the length of the transaction to a minimum or conduct the transaction during times when others do not need access.
All IDX index files (non-structural, or non-CDX based, indexes) must be closed during transactions. Only structural indexes are supported within transactions.
The following commands and functions are not supported during a transaction:
Commands and functions |
|
|---|---|
ADD TABLE |
DELETE CONNECTION |
APPEND PROCEDURES |
DELETE DATABASE |
CLEAR ALL |
DELETE TRIGGER |
CLOSE ALL1 |
DELETE VIEW |
CLOSE DATABASES1 |
MODIFY CONNECTION |
COPY INDEXES |
MODIFY DATABASE |
COPY PROCEDURES |
MODIFY PROCEDURE |
CREATE CONNECTION |
MODIFY VIEW |
CREATE DATABASE |
REMOVE TABLE |
CREATE TRIGGER |
RENAME TABLE |
CREATE VIEW |
REQUERY( ) |
CREATE SQL VIEW |
|
1 If CLOSE ALL is issued while a transaction is in progress, all tables in all open databases are closed. However, the databases remain open. Issuing CLOSE DATABASES within a transaction closes all tables in the current database, but the database remains open.
Also, the following commands and functions cannot be issued for a specific table participating in a transaction:
Commands and functions |
|
|---|---|
ALTER TABLE |
MODIFY STRUCTURE |
CREATE TABLE |
PACK |
CURSORSETPROP( ) |
REINDEX |
DELETE TAG |
TABLEREVERT( ) |
INDEX |
ZAP |
INSERT |
|
Example
In the following example, the customer table in the testdata database is opened. Optimistic table buffering is set for the customer table. The contents of the cust_id and company fields are displayed, and then the contents of the company field are replaced within the buffered data.
BEGIN TRANSACTION is issued to start a transaction. The TABLEUPDATE( ) function is used to write the changes to the table. The new contents are displayed, and ROLLBACK is issued to restore the original contents of the company field. The cust_id and company fields are displayed again with the company field containing its original values.
CLEAR
CLOSE DATABASES
* Transactions are only supported within a DBC
OPEN DATABASE (HOME(2) + 'Data\testdata')
SET MULTILOCKS ON && Required for buffering
USE customer
=CURSORSETPROP("Buffering",5)
? 'The original company field'
LIST FIELDS cust_id, company NEXT 5
REPLACE ALL company WITH "***" && Change field contents
BEGIN TRANSACTION
=TABLEUPDATE(.T.)
GO TOP
? 'The modified company field'
LIST FIELDS cust_id, company NEXT 5
ROLLBACK && Restore original field contents
=TABLEREVERT(.T.)
GO TOP
? 'The restored company field'
LIST FIELDS cust_id, company NEXT 5