The LA Fox Developer Newsletter

November 1997

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 con-

necting 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, perfor-

mance 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)

(Con’t, page 8)

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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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