The LA Fox Developer Newsletter

March 1998

Give the Database Container

a Second Look

by Steve Sawyer

It surprises me how many developers are working on VFP applications, but are spurning use of the database container. Giving up the database container gives up some very powerful features:

*Stored Procedures

Many folks have expressed lack of confidence in the Referential Integrity code created by the VFP RI Builder. I’ve been using this code for about 2 years now, and it wasn’t until a couple of weeks ago that I personally encountered a bug in this code. This bug didn’t show up until my error handler had to trap a failed trigger error, and turned out to be very easily corrected.

if you're one of those that is uncertain whether tu to use the code, I encourage you to generate RI code for a database you’re working on. Establish a breakpoint for a change in PROGRAMO in the watch window, and browse and edit one of the tables, deliberately causing a failed trigger. Step through the RI code as it executes. If you take the time to do this, and examine the various variables that each RI function establishes, you’ll quickly see that this code is doing almost exactly what you’d do in your own code to enforce these kinds of integrity rules.

Even if you choose to shun the RI builder, note that the list above does. not mention the RI Builder code as one of the benefits of using the database container. You can still write your own RI code, if you prefer, but you’ll still need the database container to establish triggers to call your own code, and there is no better repository for this code than the stored procedures in the DBC.

The database container represents a set of “metadata”, or “data about data” that resides in the system. The DBC provides most of the information needed to completely re-construct the database. The information that the DBC does not provide can be made part of any database system you’re working with, provided that you make the decision to use a database container instead of free tables.

One very important benefit that I failed to enumerate above, is the ability to extend the database container, establishing properties for tables, fields, relations etc. that the DBC does not provide natively. Any scheme for providing extended database

properties will most likely require use of the DBC. This avoids having to duplicate those properties that are contained in the DBC. Also, the DBC, through the “User” field in the .DBC table, provides an easy link between the DBC and any table of extended properties.

Unfortunately, due to the tragic loss of Tom Rettig and the database extension system he was working on, the only third- party database container extension system in wide use is known as DBCX. This system was embraced by Flash Creative Management, and was intended to be part of the Codebook framework. While this was not made an integral part of the original Codebook framework, there are a whole set of Codebook-specific extensions that work with DBCX. Stonefield Systems Group, authors of the Stonefield Database Toolkit, use DBCX extensively to provide sorely needed functionality to the database container, including the ability to reconstruct database headers and indexes.

[Ed. Note: Steve Sawyer is President of The Detroit Area FoxPro Users Group and a frequent contributor to FoxPro Advisor.)

Instantiated Windows (Con’t from page 5)

The INIT method of the Projlrak form receives the project name as a parameter, then sets the form caption to this value. This n the form a u niuque window caption. Thus, if the user clicks the “Display Project” button again, then the existing window is displayed.

[Ed. Note: Charlie Parker is a Senior Practice Partner with Fowler Software Design in Eldorado Springs, CO, and a member of The Rocky Mountain FoxPm Users Group.)

Just a Reminder.

1st Conference Price Break

Ending

The deadline for the first price break of The Second Annual Southern California Visual FoxPro Conference is fast approaching. After March 31st, the registration fee for this event will jump from $350 to $425. Please see page 9 for the registration form and all the details. So if you’re planning on attending, now is the time to get your reservation in that is, if you like saving money.

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