Re: Inverse to-one relationships
Re: Inverse to-one relationships
- Subject: Re: Inverse to-one relationships
- From: David Avendasora <email@hidden>
- Date: Thu, 22 Jul 2010 17:03:31 -0400
Hi Paul,
I'm not 100% clear on how this is modeled.
1) Does the A.b() relationship propagate PKs?
2) Are you saying that the A.b().a() may be null? In other words, are you saying A.fetchAllAs().valueForKey(B_KEY) may not return an Array with the same objects that B.fetchAllBs(ec, B.A.isNotNull()) ?
Dave
On Jul 22, 2010, at 8:00 AM, Paul Hoadley wrote:
> Hello,
>
> I know this topic comes up on the list from time to time, but I just need a quick sanity check.
>
> I have two entities, A and B. For every A, there is a corresponding B. For some subset of all Bs, each has a corresponding A. Currently I have modelled this with a single relationship from A to B, so that's a mandatory to-one relationship. (Alternatively, I could have modelled it with an optional to-one relationship from B to A.)
>
> At different times, I need to traverse this relationship in both directions. For any A, A.b() will give me the related B. But for the reverse direction, say I have a B and I want its A (if it has one), I have a custom method B.a() which does a fetch for the A such that A.b() is the B of interest. Sometimes, though, I just want to know if there is an A for a particular B, or whether it's null, and in this setting, the fetch is expensive.
>
> Here's where I need the sanity check: is there a way, given the constraints above, to model an inverse to-one relationship from B to A such that it appears as the inverse to EOF? That is, such that calling, say, A.addObjectToBothSidesOfRelationshipWithKey(B, "b") does both A.setB(B) and B.setA(A)? I'm assuming there's not, as I certainly can't beat the model into doing it. I can work around it by doing the right thing at creation time for every A, I just wanted to know if I was missing something where EOF (or Wonder) would handle this automagically.
>
>
> --
> Paul.
>
> http://logicsquad.net/
>
>
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