Hi all, One reason why ORMs have an issue trying to map objects to tables is the lack of distributed foreign keys. They can be used to easily handle subclassing, for example. One explanation is at:
http://blogs.conchango.com/davidportas/archive/2007/01/08/Distributed-Keys-and-Disjoint-Subtypes.aspx http://tinyurl.com/26hpwz They can also be used to handle missing information (NULL values), though the performance characteristics can be quite bad for this: http://www.hughdarwen.freeola.com/TheThirdManifesto.web/Missing-info-without-nulls.pdf http://tinyurl.com/ytzeyd In any event, it would potentially be a useful feature to support in Rose since I know of no SQL DBMS which supports this. For example, consider a 'My::Server' abstract base class, represented by the 'servers' table. An individual server in the 'servers' table must be in the 'dedicated_servers' table or the 'shared_servers' table, but not both. Each of the latter tables would have a 'server_id' field which a foreign key constraint against the 'servers' table. Each server record would have a distributed foreign key requiring that for each server, there is one and only *one* corresponding record in *one* of the other tables. Does that make sense? A simple syntax could be: distributed_keys => [ server => { dedicated => { class => 'My::Server::Dedicated', key_columns => { id => 'server_id' }, }, shared => { class => 'My::Server::Dedicated', key_columns => { id => 'server_id' }, }, } ], Cheers, Ovid -- Buy the book -- http://www.oreilly.com/catalog/perlhks/ Perl and CGI -- http://users.easystreet.com/ovid/cgi_course/ ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Rose-db-object mailing list Rose-db-object@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/rose-db-object
