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Mark Reichert
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 Posted: Thu Jan 18, 2007 3:36 am Post subject: TDataModule as Persistence Manager |
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From http://bdn1.borland.com/article/borcon/files/9022/paper/9022.html
Isolating these layers and decoupling their interaction then results in a
programming architecture that looks like
GUI
\
Presentation Manager/Abstraction Layer
/
Object Layer (problem domain code)
\
Persistence Manager/Abstraction Layer
/
Database
As I mentioned in the "Data Access Layer and Data Modules" thread, I was
already wanted to make it GUI-Business Class-Data Module-Database. I'll
have to give more thought to how the Business Class would be seperated into
a Presentation Manager and Object Layer, if they even need to be.
Making a TDataModule act solely as the Persistence Manager might help with
the downside mentioned here:
*****
Dataset/Datamodule based approach. Base your business object on a class that
Delphi already provides for you for handling persistence issues, the
TDataModule. The program on the front end uses the business object exposed
by the datamodule but does not ever access the persistence internals
directly. Alternatively, derive a custom TDataSet descendent that
understands its own rows as representing the properties of a specific object
class.
Upside: this is a cake-and-eat-it-too approach if you're a fan of data-aware
controls, because if you do it right you can expose business object
properties to DA controls in your front end as TFields.
Downside: Descending from a data module or data-oriented object means that
while you may provide OO methods and properties, you can't really achieve OO
containment-it may be too easy and too tempting to bypass the object
structure.
******
I'm not really interested in the Upside mentioned since I'm not using DA
controls. I am interested in using the standard methods with interacting
with databases provided by Delphi 2005, and a TDataModule makes a nice
standard container for the IBSQLs and IBDataSets I'm using. |
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Mark Reichert
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| Posted: Thu Jan 18, 2007 11:48 pm Post subject: Re: TDataModule as Persistence Manager |
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"Mark Reichert" <mark (AT) messagelink (DOT) com> wrote in message
news:45ae9614$1 (AT) newsgroups (DOT) borland.com...
I found this post from Mr. Niddery five years ago as well:
http://groups.google.com/group/borland.public.delphi.oodesign/msg/4449022e204b5f6e?hl=en&
The state of the art has undoubtably moved on from then, but I'm having a
hard time finding the proper documentation. |
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Bart
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| Posted: Fri Jan 19, 2007 12:33 am Post subject: Re: TDataModule as Persistence Manager |
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| Quote: |
The state of the art has undoubtably moved on from then, but I'm having a
hard time finding the proper documentation.
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I also had a hard time to find proper documentation. Especially in Delphi.
But a few days ago I found something in C#. It is called CSLA. It is open
source and the author wrote a good book about it.
http://www.lhotka.net/cslanet/
if you search the net you find a lot of resources about this framework.
Maybe it is usefull for you to study.
Regards,
Bart |
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Bob Dawson
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| Posted: Fri Jan 19, 2007 12:45 am Post subject: Re: TDataModule as Persistence Manager |
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"Bart" wrote
| Quote: | But a few days ago I found something in C#. It is called CSLA. It is open
source and the author wrote a good book about it.
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CSLA is not a persistence framework--it's an object remoting framework. Very
different.
bobD |
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Bart
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| Posted: Fri Jan 19, 2007 12:54 am Post subject: Re: TDataModule as Persistence Manager |
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| Quote: |
CSLA is not a persistence framework--it's an object remoting framework.
Very
different.
So I do understand this wrong ?: |
"CSLA .NET is designed to allow great flexibility in object persistence, so
business objects can use virtually any data sources available. The framework
is designed to enable single tier and n-tier models through the concept of
mobile objects. This provides the flexibility to optimize performance,
scalability, security and fault tolerance with no changes to code in the UI
or business objects"
Bart |
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Bob Dawson
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| Posted: Fri Jan 19, 2007 1:14 am Post subject: Re: TDataModule as Persistence Manager |
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"Bart" wrote
The important bit:
| Quote: | "The framework
is designed to enable single tier and n-tier models through the concept of
mobile objects."
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CSLA doesn't care what the ultimate persistence layer is, but then neither
does it provide it.
My caution that it's not really a persistence layer is based on direct
conversation with the author--who corrected me when I made the same mistake.
I had lunch with him at a conference last spring. After adopting CSLA you
still have to provide the persistence layer on the back end.
For a discussion of using both CSLA and a persistence framework at the same
time, google 'CSLA NHibernate'.
bobD |
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Bart
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| Posted: Fri Jan 19, 2007 1:37 am Post subject: Re: TDataModule as Persistence Manager |
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| Quote: | My caution that it's not really a persistence layer is based on direct
conversation with the author--who corrected me when I made the same
mistake.
I had lunch with him at a conference last spring. After adopting CSLA you
still have to provide the persistence layer on the back end.
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Thank you for clearing this.
Bart |
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Bob Dawson
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| Posted: Fri Jan 19, 2007 10:58 pm Post subject: Re: TDataModule as Persistence Manager |
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"Bart" wrote
| Quote: |
Thank you for clearing this.
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No problem.
And I didn't mean to slight CSLA. There is a lot of functionality in CSLA in
terms of support for business rules, object validation, etc.--much of the
business of a business object layer. It's just that if you're interested in
studying an OPF codebase specifically, it's probably not a good candidate.
In the .NET realm I'd probably recommend Gentle.NET as something to look at:
http://sourceforge.net/projects/gopf
http://www.mertner.com/confluence/dashboard.action
There's a pretty good review of .NET ORMs here if gentle in particular
doesn't appeal to you
http://www.howtoselectguides.com/dotnet/ormapping/
A lot of core OPF thinking traces back to Scott Ambler's paper
http://www.ambysoft.com/downloads/persistenceLayer.pdf
His site has several interesting papers to read besides that one.
Best source I know for OPF references and design discussions in Delphi is
this forum.
bobD |
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Andrea Raimondi
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| Posted: Wed Jan 24, 2007 9:16 am Post subject: Re: TDataModule as Persistence Manager |
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Hi Mark,
Personally, I use this approach:
TDataModule->Opf classes
I define my "operations" in the Datamodule and then call the opf
classes internally to actually do them.
It's a flexible approach and works.
Cheers,
Andrew |
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