[Dbix-class] Re: Three table relationships?

[Matt S Trout]

On 2 Feb 2007, at 20:21, A. Pagaltzis wrote:

> * Zbigniew Lukasiak <zzbbyy at gmail.com> [2007-02-02 13:25]:
>> select * from a, b, c where
>> a.key1 = b.key2 and b.key1 = c.key2 and c.key1 = a.key2
>>
>> With composed (key1, key2) primary keys for a, b and c tables.
>>
>> This join is a three table relationship (just like the many to
>> many case) - and I think it is not reducible to a superposition
>> of two table relstionships (differently from the many to many
>> case).
>
> Heh. And unless you weaken your FK constraints, you will never be
> able to insert a row into these tables. :P  (Except maybe with
> some kind of multiple-table insert support, using a view or
> whatever.)

Or by using a delayed FK and inserting into all of them during a  
transaction.

Unless you're using MySQL, which doesn't support this because it's a  
fucking toy (insert relational dildo management system joke here).
>
>> To reiterate - I did read your thesis that many to many is not
>> a relatioship - so you don't need to repeat that - I am just
>> asking why it is not and what is a relatioship.
>
> I think a relationship is anything you can say in SQL DDL.

Pretty much. Supporting more complex -relations- ala m2m is cool, but  
they're a different beast.
-- 
Matt S Trout, Technical Director, Shadowcat Systems Ltd.
Offering custom development, consultancy and support contracts for  
Catalyst,
DBIx::Class and BAST. Contact mst (at) shadowcatsystems.co.uk for  
details.
+ Help us build a better perl ORM: http://dbix- 
class.shadowcatsystems.co.uk/ +