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OOP: Better OOP part 6 2003-04-23 -- Dan Pressnell Newsgroups: comp.lang.clarion,topspeed.topic.oop
March 5, 2006:
Note that the code is now available at:
http://www.icetips.com/downloadfile.php?FileID=59
If you've downloaded the sample OOP app from
http://toolwares.com/oop_sample.ZIP, download it again, because I've added
more to it.
In the sample app, I'm using a Microsoft Access database. In the class
methods that retrieve the data, I use a variation of one technique that I
described in my SQL articles, so it might look a little strange to have a
Clarion program getting data that way.
If you prefer, you can use Clarion's file structures with VIEWs and ABC file
access. Look at the new procedure ShowTeamsWithView. That procedure looks
almost identical to the ShowTeams procedure. Neither give any indication of
how the data is retrieved from the database.
The ShowTeamsWithView procedure instantiates the TeamsClass2Type class,
though. That class uses a VIEW and the ABC RelationManager, as you can see
in the class by looking in the Classes:1 "procedure."
In the TeamsClass2Type.Getdata method, a view is declared, the ABC
RelationManager is opened for a file, a buffer for the view is set, the sort
order of records retrieved is specified, and the data is loaded into a
queue. Then the VIEW and the RelationManager is closed.
There is an additional call to a method in the class to calculate the total
of the TeamID field in the records. While you will rarely have to caculate
the sum of ID fields, it serves as an example of what I call post-query
processing. That is, after the query, you have additional work to do on the
retrieved data, such as totalling or summarizing.
When using ABC (or other Clarion FILE processing) to retrieve data in a
class, always be aware of the possibility that you will trash a record
buffer that some other part of the program relies on. If you do trash it,
document it so other programmers will know--and you will remmber--and can
take steps. Because the class declaration is good mini-documentation for a
class, you usually need no more than a small comment. (See the declaration
of the TeamsClass2Type class.)
To preserve record buffers, see the documentation on the
FileManager.SaveFile and FileManager.RestoreFile methods in Clarion's help
system. You can implement that in the class if you want, before and after
the data retrieval.
=====
By the way, I've changed the way the exported CSV file is viewed in the
sample app. It now loads Excel with the CSV file if you have Excel on your
system and it's set up with CSV as a file association. If you don't have
Excel, see the code for the csvExporterClassType for how to do something
else.
Also note that I've moved the code for the
GeneralClassType.GenericQueueViewer method to a class all by itself, and now
I simply have GeneralClassType.GenericQueueViewer use that class. Classes
allow you to make changes to enhance functionality like that, without
breaking any code elsewhere in the program.
Dan
Today is November 21, 2024, 3:45 am This article has been viewed 35384 times. Google search has resulted in 17 hits on this article since January 25, 2004.
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