x

To make changes to a data source, you issue the write commands: INCLUDE, UPDATE, REVISE, or DELETE. These perform the same functions as the MODIFY commands of the same names. In Maintain, however, these commands are enhanced so that you can perform a transaction for:

• A set of records, using the FOR ALL prefix and the FROM phrase.
• A sequence (subset) of records, using the FOR n prefix and the FROM phrase.

These phrases were described for other commands in Step 2: Selecting Records and Step 3: Collecting Transaction Values.

To guarantee the integrity of all the include, update, and delete operations comprising a single logical transaction, you code a COMMIT command immediately following the last step of the transaction. Then, if a system problem or another application interrupts the logical transaction, it is rolled back—that is, cleared—without being written to the data source. In this way, you can guarantee that no transaction component is ever written to the data source unless all transaction components are—that is, unless it is part of a complete and successful logical transaction.

x

You add an UPDATE command to update the data source. Each part of the command plays a different role:

• FOR ALL selects all of the rows in the stack with which to update the data source.
• FROM CustInfo takes the rows from the stack named CustInfo. The columns specified in the command are used to update the data source.

You define the entire procedure as one logical transaction and issue a COMMIT command to send the changes to the data source. The first stage of the procedure is now finished and looks like this:

MAINTAIN FILE VIDEOTRK
FOR ALL NEXT CustID INTO CustInfo
WHERE ExpDate GE 920601 AND ExpDate LE 920621;
WINFORM SHOW ShowCust; 
FOR ALL UPDATE LastName FirstName Street City State Zip
Phone FROM CustInfo;
COMMIT; 
-* >> Generated Code Section....
.
.
.
END

Try it now: If you have created your own set of application files, enter these additional commands into your Maintain procedure file.