Re: [Openinteract-help] has_many relationships?

[Ray Z. <rz...@co...>]

On Feb 16, 2004, at 4:26 PM, Vsevolod (Simon) Ilyushchenko wrote:

>>  If I interpret correctly what it is that you want, you're looking 
>> for the ability to define a relationship that would automatically 
>> generate methods in your "software project" object to fetch the 
>> corresponding list of bugs, for example.
>
> And vice versa, I want to be able to fetch the project object that a 
> bug object belongs to.

Right, these are the forward and reverse direction fetching methods I 
talk about. I'd have to dig back into the details again, but I think my 
design assumes you want one or the other, but not both. That could 
probably be added.

> Chris actually sent me those links a while ago. This approach may be 
> more than I bargained for, but if that's the right solution, I could 
> take a stab at it, provided Chris agrees.

Obviously, I'm biased :-), but I would rather see effort put into 
moving to this more general structure rather than adding onto the 
existing more limited one.

> However, after reading your posts it seems to me that you only talk 
> about a many-to-many relationship: you always have X between A and B.
> I really want to have a system that can handle simple cases of 
> one-to-one and one-to-many relationships with only two tables/objects, 
> as having three tables is inconvenient from the DBA's point of view 
> and should be avoided when possible.

Actually, no. I used the three classes X, A and B just to define some 
minimal notation that I could use to talk about all of the above 
relationships. For simple one-to-one and one-to-many relationships, 
just look at X and A (pretend you don't have B). See the first 3 
examples at the end of the first post.

The proposed structure just attempts to handle all of the relationships 
using a single generalized has-a configuration:

*  one-to-one:  X has-a A, X is the main object with a method to fetch 
it's corresponding A

*  one-to-many: X has-a A, A is the main object, with a method to fetch 
it's many X's

*  many-to-many: X has-a and X has-B, X is a linking object between A 
and B, and A has a method to fetch all of the linked B's (or vice 
versa).

I hope this helps.

Ray Zimmerman
Director, Laboratory for Experimental Economics and Decision Research
428-B Phillips Hall, Cornell University, Ithaca, NY 14853
phone:  (607) 255-9645       fax: (815) 377-3932