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From Jörg von Frantzius <jfrantz...@web.de>
Subject Re: Detecting inconsistencies of mapped-by declarations?
Date Thu, 07 May 2009 20:01:15 GMT
I just happened to write:
> >> Also it is possible to declare two fields in two different classes, e.g.
> >> B1.a and B2.a, with the identical mapped-by pointing to the same field
> >> of the same related class, e.g. A.a. That would mean that in theory two
> >> FKs would have to be created for the same column, pointing to different
> >> tables. That neither seems to make sense to me.
> >>     
> >
> > It makes sense to me. Same as above.
> >
> > It's not common to handle these associations in relational databases, but
> > very common when using UML.
> >   
> In UML you'd have to write something like "for any b1 of type B1 and b2
> of type B2: b1.a==b2.a" in OCL to express the above. Why should we
>   
Sorry that was utter nonsense. After thinking about really, it rather
seems to mean two mutually exclusive associations. So if an object of
type A is referenced by a B1 object through B1.a, there can be no B2
object referencing it through B2.a (and vice versa).

Implementing this using mapped-by would firstly lead to problems due to
impossibility of FK constraints, and secondly be one of the least
obvious and understandable ways of implementing it ;)

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