The LA Fox Developer

A Newsletter for FoxPro Application Developers in Southern California

Visit our WebSite at: http://www.mesllc.com/lafox.html

March 1999

Deleting and Reusing

Primary Keys

by Russell Campbell,

AFUG President and Newsletter Editor

I ran into a problem in a table in which the client assigned the

value to the primary key. The table is called PARTS and the

primary key is PARTNUM. The client has to be able to assign

the part number themselves. Using another field that they never

see as the primary key is not really an option, since PARTNUM

must be unique and would therefore be set up as a candidate

key. The problem I ran into would occur on the primary key or a

candidate key, so creating another field as the primary key was

not really an option.

What the client was sometimes doing was deleting a part and

then wanting to reenter it. This is what caused the problem.

VFP would see the deleted primary key (say part number

‘VALVEOI’) and wouldn’t let the user reenter the same part

number again. There were other ways of doing this same task.

Locating the record and changing it is the same as deleting it

and reentering it, but some users were not doing it that way for

some reason. Since there are well over 50 users on this system

and since I try to accomodate how the users want to work

instead of asking them to accomodate how the program works, I

came up with a solution.

One of the ways of allowing a primary key to be reused is to

have the primary key be based on a conditional index. In my

case, it would be”PARTNUM AND NOT DELETEDO”. This

would mean that VFP would ignore the deleted occurance of a

part number and if the user entered that part number again, VFP

would accept it just fine.

This is an acceptable solution, but what if the deleted record

ever gets recalled? Then you would have a problem. I wanted a

way to avoid that admittedly unlikely problem. What I did was

give the primary key of the deleted record a unique value that

would never be used by a user.

To do this, I added some code to my base class delete method

and called it only when instructed to do so by the delete method

on a form. Since my primary keys are usually only character or

(Con’t, page 5)

At LA Fox

March 15, 1999, 6:30 PM, Jonathan Melvin. Jon Melvin will

describe VFP-based tools he has developed to manipulate SQL

and to extract data from various ODBC databases and insert it

into SQL server. He will also describe Active Server Page

(ASP) procedures used to access the SQLserver data over the

web. These procedures are “data-driven” (the web pages are

automatically formatted to match the structure of the data they

are provided). Access is also secure. Users enter a usemame

and password, and are allowed to access only certain fields in

each table. All security (and other) parameters are passed as

form variables in the web pages so that SSL encryption will

encrypt them, rather than being passed as part of the URL (the

more usual way). This VFP/SQLserver/ASP system is used in

production systems which provide both intranet and extranet

access to data from various databases.

April 19, 1999, 6:30 PM, Rod Paddock. Rod Paddock is

president and founder of Dash Point Software, Inc. DPSI based

in Seattle, WA, specializes in developing applications and

training software developers. DPSI develops with Visual lnterdev,

VFP, VB and SQL Server. DPSI’s clients include: ADTC, SBT

Accounting, The US Coast Guard, The US Navy, Pinnacle

Publishing, Intel and Azalea Software. Rod was a featured

speaker at the 1996/1997 German FoxPro DevCons, the 1995

and 1998 Visual FoxPro Developers Conference, the 1995-1997

FoxTeach conferences, and the 2nd Annual Southern California

Visual FoxPro Conference. Rod writes for several database

publications including: Data Based Advisor, Foxtalk and Dbase

Advisor. Rod’s books include: VB5 for Web Development and

VFP 5 Enterprise Development from Prima Publishing. Both of

(Con’t, page 2)

Out and About

by Barry R. Lee

The March meeting of LA Fox will be held on

March 15, 1999, at 6:30 PM at our regular

meeting place (the Torrance Airport, 3301

Airport Drive, in Torrance). For details on

how to get there, see the map on the back

page.

In this issue

When Relations Don’t Work

FoxPro Q&A

Reapplying Default Values

Page 3

Page 4

Page 6

and much more