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The LA Fox Developer Newsletter
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November 1997
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Transaction Server
(Con’t from page 1)
This is a good example of where MTS saves the day. Each object is set up to require a transaction. If I instantiate an Account object from within a Transfer object, then the Account object inherits the Transfer object’s transaction! In this case the Transfer object creates two instances of Account. The Account object has each been written to commit or abort. They only need to know if they can commit or abort their own data. They don’t know about the other account or the Transfer object. If account object A commits because the deposit went OK and B commits because there is enough money to withdraw then the Transfer object commits and all transactions end at the same time. But if A commits and B aborts then the Transfer object aborts and A is rolled back. Yet no code must be changed in the Account objects in order to deal with this scenario.
Very cool.
Here’s another scenario. Let’s say I have lots of objects connecting to a database. Each connection takes resources and perhaps even a license, depending on the database. How do I manage them so I don’t have too many or so I’m not opening and closing connections constantly? In VFP 5 I use an out-of- proc server with views that share connections. The server opens a connection in the default data session and keeps it open so that other views, in private data sessions, can share it. Works OK, but isn’t very scalable and requires that all the components work in that process.
With MTS, the Connections are pooled with a connection manager. When I create an object that needs a connection the manager looks for an unused Connection and uses it if it can. Then, when I attempt to send back data the manager will go back into the pool and reallocate a connection. This keeps the number of connections to a minimum and improves performance without me having to do any stupid tricks like I have to do now.
These are just two examples of how MTS can greatly simplify the life of a developer, while increasing the robustness, performance and efficiency of application components.
[Ed.Note: Gary DeWitt is the senior software
Wizard
for MedSoft Inc, a medical software company located in Sunny Lake Tahoe, CA, USA. Gary is a regular contributor to FoxPro Advisor, Fox Talk, the Virtual FoxPro User Group Newsletter and other software related publications. Gary is also a FoxPro MVP and holds other certifications from Microsoft as well.
Formore
on Microsoft Transaction Server (MTS):
http://www.microsoft.com/transaction/default.asp
http:/i204. 203.124. 10/pdc/html/seybold.htm
(600k Word DOC file download available)
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The LA Fox Developer’s Group has entered into an agreement with Macmillan Computer Publishing. LA Fox members can now purchase all Macmillan Computer Publishing titles at a discount of 30% off retail pricing.
Macmillan owns the following publishers:
Que
New Riders Press
The Waite Group
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Que Education & Training
Macmillan Technical Publishing
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With all these publishers and over 40% market share, Macmillan has the best books for Computer technology.
To take advantage of this offer, you must be a member-in-good- standing (read current and paid-up) and have a credit card. You can receive our special account number and the 800 access number by calling me at 800/499-6237 or 714/375-3300, ore- mailing me at CompuServe (72723,3422) or brlee@earthlink.net.
FoxPro Q&A
(Con't from page 6)
x.f.
return .t.
else
x.t.
return .f.
endif
Now preview the report and you will find Alternate lines shaded grey.
Q Can I change the description of one or more radiobuttons as the program runs?
A You can use the SHOW GET command with the PROMPT clause to programmatically change the prompt of the radiobuttons.
Example: If the variable name is, say ‘rb’, and you have three buttons in the radiobutton set, then use:
SHOW GET rb,1 PROMPT “abcd”
SHOW GET rb,2 PROMPT "abc"
SHOW GET rb,3 PROMPT “ab”
[his changes the prompts to ‘abcd’,’abc’ and ‘ab’.
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