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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: GNATColl ORM problem (foreign key twins)
Date: Wed, 30 Oct 2013 12:43:51 +0000
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Date: 2013-10-30T12:43:51+00:00
List-Id: <comp.lang.ada>

Jacob Sparre Andersen <jacob@jacob-sparre.dk> writes:

> I want to model a collection of categories and subcategories in a
> database like this:
>
> | TABLE    | categories          | category        |  | Item categorisations |
> | name     | Text                | PK              |  |                      |
>
> | TABLE    | category_subsets    | category_subset |  | Item categorisations |
> | superset | FK categories(name) | NOT NULL        |  |                      |
> | subset   | FK categories(name) | NOT NULL        |  |                      |
>
> But this fails because GNATColl names the foreign key fields with the
> referenced field name instead of with the referencing field name.

I think that the problem is that the thing in brackets is not meant to
be the PK in the table that is being referenced, it's the name of the
reverse relationship. Look for 'revert_name' under [1] (I'm pretty sure
this should be 'reverse_name', BTW).

So yours would be

| TABLE    | category_subsets     | category_subset |  | Item categorisations |
| superset | FK categories(parents) | NOT NULL        |  |                    |
| subset   | FK categories(children) | NOT NULL        |  |                    |

and you get a function Parents that takes a Category and returns (a list
of?) Categories (a Category_Manager?).

[1] http://docs.adacore.com/gnatcoll-docs/sql.html#database-schema