1:N and 1:1 using link table

Well... working or not, there is flaw in such design.

The link table should have a single PK only on store_id, otherwise the
table could hold N:M relations instead of 1:N relations, and if there
was a way of having a 1:1 relation back using the link table, such
relation wouldn't be resolved because of several rows in the link
table.

Other than that I don't know if it still could work.

Regards!

Esteban A. Maringolo


2014-10-22 12:01 GMT-03:00 Esteban A. Maringolo <[hidden email]>:
> Is it possible to have a 1:N (ToManyMapping) using a link table, and
> also a 1:1 mapping using the same link table?
>
> Ej:
> Let's suppose I have a list of Supervisors and a list of Stores.
> One supervisor can have serveral stores (1:N).
>
> On the other side, each store can have only one supervisor.
>
> I tried using the descriptors described below, but I'm getting an
> error with error:
> 'Joins should go to the table(s) associated with the reference class
> of the mapping' in OneToOneMapping(RelationshipMapping)>>#validate:
>
> I couldn't find an example for this in the tests.
>
>
>
> On the Supervisor descriptor I have:
> (aDescriptor newMapping: ToManyMapping)
>   attributeName: #stores;
>   referenceClass: Store;
>   usesLinkTable: true;
>   collectionType: Set;
>   beExclusive;
>   join: (Join
>     from: (table fieldNamed: 'id')
>     to: (storesLinkTable fieldNamed: 'supervisor_id')).
>
> On the Stores descriptor I have:
> (aDescriptor newMapping: OneToOneMapping)
>   attributeName: #supervisor;
>   referenceClass: StoreSupervisor;
>   join: (Join
>     from: (table fieldNamed: 'id')
>     to:  (storesLinkTable fieldNamed: 'store_id')).
>
>
> If I remove the join: I get the error:
>  'Cannot automatically determine join, too many constraints found.'
>
> Because the table Store also have other 1:1 references to the class
> Supervisor (with an explicit join), of which StoreSupervisor is a
> subclass, and Supervisor is the root of a filtered type resolver.
>
>
> Regards!
>
> Esteban A. Maringolo

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