(no subject)

I will be there!
Looking forward to meet you all.

Johan

On 07 Sep 2010, at 20:07, Dale Henrichs <[hidden email]> wrote:

> Just out of curiousity, who will be making it to ESUG this year?
>
> We should try to grab a GLASS lunch table together on at least one of the days so we can swap war stories face to face ... although perhaps it would be more familiar to sit at separate tables and send email back and forth:)
>
> Dale

Ok, I'm working towards a better understanding of GemStone. I still have
a few problems adopting to the OO approach in GemStone well and how to
get data from RDBS into GemStone.

First question:
I read about GemConnect, but it seems this is just "suitable" for Oracle
DB. Well how do I get access to other RDB in a way to "migrate" Data to
GemStone?

Second Question.
Still due to my limits of how to structure an OO Solution.

Let us assume I have an order whith order items.
So one order can have 1 or more order items.

I surely have to keep track of the orders. So in an RDB I would probaly
would have a field OrderID, and let's name it order_id_items and probably
ArticleID (of course a few others also)

but it would be kept in table on it's own
with three fields
OrderID OrderItemID ArticleID.
  1         1         ArtID-01
  1         2         ArtID-02
.....

Would one do it similiar in GemStone. Having a class Order with an ID an
orderID instance variable or something different?



Regards
Friedrich

Hi Friedrich,

Perhaps I can give it a shot to help a bit...

> I read about GemConnect, but it seems this is just "suitable" for Oracle
> DB. Well how do I get access to other RDB in a way to "migrate" Data to
> GemStone?

If the migration is once-off (in the sense that you'd not keep
updating the RDB and have to do it frequently), then I'd do this:
write each table out to a text file (csv or something like that)
create a class in GS for each table
use CSVParser to import each table into a collection of instances of the class
write beautiful Smalltalk code to convert these tables to the OO
structures you have in GemStone

If you need to get data from your RDB continually, you could hear from
the GemStone if GemConnect can work for the RDB of your choice.

Otherwise, you can use something like http://www.glorp.org. I remember
something about the VisualWorks guys have a port that's been kept up
to date. I did not find one on http://seaside.gemstone.com/ss, but a
port should not be a huge job?

> I surely have to keep track of the orders. So in an RDB I would probaly
> would have a field OrderID, and let's name it order_id_items and probably
> ArticleID (of course a few others also)

You'll have a class called Order in GS. Then, if you use the order id
for something like printing it on a document (for reference by a
user), you'll have an instance variable called "id".

> but it would be kept in table on it's own
> with three fields
> OrderID OrderItemID ArticleID.
>  1         1         ArtID-01
>  1         2         ArtID-02

You'll also have a class called Article. If the same condition applies
as the order, you'll have an instance variable called "id" on Article.

With the info you provided here, you only need an instance variable
called "articles" on your Order, which you initialize to be an empty
Collection. (Each Order have it's own collection of Articles.) Then,
you'll add Article objects to this collection (write a method on Order
called addArticle: or something like that.)

This is possibly insufficient as you'll need to carry something like
"quantity" and "price" in a OrderItem. So, create a class by this name
and rename "articles" on Order to "items". For each Article in the
Order, create an OrderItem and add it to the order (with
addItem:quantity:price: In this method, create an OrderItem, carrying
the necessary fields.)

I like the practice of referring back to the Order from the OrderItem,
and even from the Article to a collection of OrderItems (to find all
orders for an article to manage stock, or something). Arguably, you
can derive the relationships. Also, having a unidirectional reference
makes maintaining integrity easier.

But still, I like adding "cross" references because this just makes
the Object system very powerful. For example, when I build a web page
showing an Article, it's no sweat to list Orders for this Article.

HTH
Otto

Friedrich, 

Sean Allen <[hidden email]> writes:

> Friedrich, 
>
> Is the order system an academic question or are you working on an e-commerce/
> order system?
It is a bloody serious commerce system for the waste management industry
Well it's at least that serious that it earned my living ;-).

If anyoone like to get in touch with me about it, just drop me a note...

I'm currently figuring out the diverse options...

Regards
Friedrich


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You can contact me off list if you want and we can go through example Gemstone designs if you want.