De: Paul McNett <[EMAIL PROTECTED]>
Data: Terça-Feira, 24 de Abril de 2007, 18:10
Assunto: Re: [dabo-users] Strategies for populating controls with data from
many-to-many relation
> Hi Miguel,
>
> I'll try to help you out with this over the next day or so (really
> busy
> now) but scroll down because I do answer a couple of your specific
> questions.
>
>
> > I'm wondering what would be the best strategy (and alternatives)
> to populate a control with data from a many-2-many relation.
> >
> > Here's the setup (You can find this Demo In Progress in the Wiki
> under "Demos in Progress":
> > book.book_id (table.table_pk)
> > bookauthor (link table, fields: bookauthor_id, book_id, author_id)
> > author.author_id (table.table_pk)
> >
> >
> > Objective:
> > Populate a dListBox in a form where the primary bizobj
> datasource is book. Everytime one changes book the dListBox gets
> populated with the name of the related authors. I've read the
> WikiPage "How To Populate and Use List Controls" but I can't get
> much from it for this particular cross-table dynamic context.
> >
> > 1 - My feeling is that dabo can take care of this for me (is
> this true?).
> >
> > Do I accomplish this by chaining bizobjs? I mean make bookBizobj
> parent of BookAuthorBizobj and BookAuthorBizobj parent of
> RelatedAuthorBizobj! I've tryed this approach without any
> complaints from Dabo (no exceptions raised), but I'm unable to
> figure out to populate the dListBox. The code in the WikiPage
> reflects these changes.
>
> For 1:M joins, bizobj chaining works very well because Dabo
> handles
> requerying the children automatically. M:M joins should work as
> well
> chained like this but I haven't done it that way in the past.
I have no special requisite to make it in one way or another. Actually I would
prefer the approach that is most maintainable in growing projects that could
turn out quite large. This is my favorite way of coding anything - sounds like
I'm a paper-plane chasing perfectionist :-( !!!
> > My difficulty comes from the fact that I have to bizobjs with
> the same DataSource.
> > * AuthorBizobj - used to populate the Authors Grid on page two
> (working like a charm - txs guys ;-)
> > * relatedAuthorBizobj - to be used to populate the dListBox
> (as per above)
>
> self.Form.getBizobj("author") will return your authorbizobj
> because
> you've done self.Form.addBizobj(bizAuthor). Keep a separate
> reference to
> relatedAuthorBizobj without doing Form.addBizobj() with it.
Usually Mickey Mouse solutions are amongst the best. Txs for the tip.
> > 2 - If dabo can't do this for me what would be the soundest
> approach?> * Should bizobjs be used?
>
> Dabo doesn't offer full-automatic handling of M:M joins, but it
> isn't difficult once you've done it once. The ListBox needs a DataField
> to save to (this would be a field in the join table) as well as a
> source of values to list (this would be your authorBizobj.author_name
> field).
> Again, I'll get back with concrete examples as soon as possible.
>
> Yes, bizobjs should definitely be used.
I see what you mean. I'll be saving book_id's and author_id's and displaying
related authorname's.
> > BTW: Is there a way to get a bizobj or a dataset with fields
> from two tables?
>
> Yes, although it won't save changed fields from other than the
> main
> table (the DataSource one). Just write your sql appropriately:
>
> biz.UserSQL = """
> select book.name as book_name,
> author.name as author_name
> from book
> left join author_book
> on author_book.book_id = book.id
> left join author
> on author.id = author_book.author_id
> """
>
> --
> pkm ~ http://paulmcnett.com
Sure. I was wondering more in the direction of an updatable view.
Thank you very much for the time and tips. I have plenty of exploring to do now.
Thanks again,
Miguel
_______________________________________________________________________________________
Aqueca o seu Inverno com o credito pronto a usar!
Saiba mais em http://www.iol.pt/correio/rodape.php?dst=0701181
_______________________________________________
Post Messages to: [email protected]
Subscription Maintenance: http://leafe.com/mailman/listinfo/dabo-users
Searchable Archives: http://leafe.com/archives/search/dabo-users
This message: http://leafe.com/archives/byMID/dabo-users/[EMAIL PROTECTED]
