How to Preserve Index Expressions to Rebuild CDX and Tags

• Microsoft Visual FoxPro for Windows, version 3.0
• Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b, 2.6, 2.6a
• Microsoft FoxPro for MS-DOS, versions 2.5, 2.5a, 2.5b, 2.6, 2.6a
• Microsoft FoxPro for Macintosh, versions 2.5b, 2.5c, 2.6a
• Microsoft FoxPro for UNIX, version 2.6

SUMMARY

Often, a utility menu is included in an application that enables the user to perform functions such as reindexing or backing up files. One very useful function to include on such a utility menu is a way to recreate the .CDX file with all of the tags rebuilt programatically. This keeps the .CDX file in optimum condition if done routinely. This article shows by example how to do this.

MORE INFORMATION

You first need to store the tag names and index expressions in a utility table. Then you need some code to read the utility file that will use the values to reindex the table.

Sample Code

* Make the CDX Expression table.

CREATE TABLE cdxexp ;
   (TAG C(10),expression C(254))

* Insert three index expressions into the table.
* Below is a simple index expression on one field.

INSERT INTO cdxexp ;
   (TAG,expression) ;
   VALUES ;
   ("COMPANY","company")

* Below is a concantenated index expression.

INSERT INTO cdxexp ;
   (TAG,expression) ;
   VALUES ;
   ("STATE_CO","ALLTRIM(UPPER(state))+ALLTRIM(company)")

* Below is a complex index expression that correctly orders a numeric
* field concantenated with a character field. Indexing on the STR() of
* a numeric alone will yield incorrect ordinal values of the numeric
* field. This expression uses PADL and ALLTRIM with STR to put the
* numeric characters into the correct location in the string.

INSERT INTO cdxexp ;
   (TAG,expression) ;
   VALUES ;
   ("YTDP_ST","PADL(ALLTRIM(STR(ytdpurch,20,2)),20,'0') + ;
   ALLTRIM(UPPER(state))")

* Use the library FoxTools for the MessageBox function.

SET LIBRARY TO foxtools
SET DEFAULT TO c:\fpw26a\tutorial

* Delete the current CDX file in order to rewrite the header.

IF USED('CUSTOMER')
   SELECT CUSTOMER
   USE
ENDIF
DELETE TAG ALL

* Open the table to reindex (CUSTOMER.DBF) in the second Workarea.

SELECT B
USE C:\FPW26A\TUTORIAL\CUSTOMER

* Call the MsgBox function from FoxTools with "Yes/No" buttons, option 4.
* The MsgBox function will need to be replaced with a GET object for
* versions other than Windows.

msg="Ready to rebuild the CDX file?"
answer=MSGBOX(msg,"",4)

* If the user clicks the Yes button, the return value will be 6.

IF answer=6
   SELECT A                  && index expression file called "cdxexp"
   GO TOP
   DO WHILE NOT EOF()        && process the whole file
      mtag=cdxexp.tag        && read the values from the record
      mexp=cdxexp.expression
      SELECT B
      INDEX ON &mexp TAG &mtag   && index on the variable expressions
      SELECT A
      SKIP                   && go to the next record
   ENDDO
ENDIF

* End of program. 

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Keywords : kbcode FxprgGeneral
Version : 2.5x 2.60 2.60a 3.00| 2.5x 2.60
Platform : MACINTOSH MS-DOS UNIX WINDOWS
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