Re: To-one relationship always returns a fault
Re: To-one relationship always returns a fault
- Subject: Re: To-one relationship always returns a fault
- From: Art Isbell <email@hidden>
- Date: Thu, 29 Apr 2004 20:30:18 -1000
On Apr 29, 2004, at 7:52 PM, Greg Hulands wrote:
In my model I have two entities, one Product and the other
ProductImage. Currently there are no records in the ProductImage table
as I am just implementing this functionality. The only problem is that
Product always returns a fault for the image, eg product.image()
instead of returning null. In the model I have the Product owning the
image and have the relationship as optional.
The logical way to model this would be for the foreign key for the
Product.image relationship to the Product's primary key. If that's
what you've done, consider the problem that this causes. An optional
to-one relationship would mean that the foreign key value would be null
when no relationship object exists. But the foreign key can't be null
because it's Product's primary key. This problem is discussed at
http://developer.apple.com/documentation/WebObjects/UsingEOModeler/
5WorkingWithRelationships/chapter_5_section_4.html#//apple_ref/doc/uid/
TP30001018-DontLinkChapterID_4-BABHGAAA:
"A to-one relationship from one foreign key to a primary key must
always have exactly one row in the destination entityif this isnt
guaranteed to be the case, use a to-many relationship. This rule
doesnt apply to a foreign key to primary key relationship where a null
value for the foreign key in the source row indicates that no row
exists in the destination."
If this doesn't apply to your situation, please elaborate on how
you've modeled this relationship.
Aloha,
Art
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