Re: [Objectbridge-developers] optional relationships

[David F. <dw...@la...>]

At 10:55 PM 8/9/2001, Dirk Olmes wrote:
>David Forslund wrote:
>
> > > To illustrate things better I'll just give a short description of my
> > > tables: I have a table 'Person' which has a to-many relationship to
> > > the table 'Folder'. The 'Folder' table will later have a reflexive
> > > relationship to itself (so I can have subfolders to every folder).
> > > (BTW: is that possible with ObjectBridge right now?)
> >
> > Yes, it does.   We are using it this way now.  One of my applications
> > has the same structure.  It has an "Identity: object which contains many
> > "Traits" Traits can contain other Traits.  I have two tables Identity 
> and Trait
>[...]
> > > In order to model that, the 'Folder' table needs a foreign key which
> > > can be NULL for the case that a folder has no parent folder.
> >
> > In my case I don't allow for a Trait to exist by itself, so a Trait
> > has a Trait or an Identity as a parent.   I don't formally use a 
> foreign key.
>
>Good to hear that. But how do you do the mapping? I currently have no
>idea how to accomplish that without a foreign key. Or do you put code
>into Trait to retrieve the parent?

The Trait doesn't need to retrieve the parent (but it can return the id of 
its parent if it needs to be retrieved),
but I do have code for the parent to retrieve the child if it isn't 
present.  I think the OJB examples do not have foreign keys, 
either.  Several DBMS' I deal with don't handle foreign keys correctly, anyway.


Dave


>-dirk
>
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David W. Forslund                               dw...@la...
Computer and Computational Sciences             http://www.acl.lanl.gov/~dwf
Los Alamos National Laboratory          Los Alamos, NM 87545
505-663-5218                                    FAX: 505-665-4939