I have a table that stores a user ID and a subscription type, and this is really all it needs to store and any pair of values will always be unique. In fact, I think this pair should be the primary key on the table. However, I'm using Castle ActiveRecord which says at:
http://www.castleproject.org/activerecord/documentation/v1rc1/usersguide/pks.html#CompositePK
And I quote:
Quick Note: Composite keys are highly discouraged. Use only when you have no other alternative.
I get the feeling they're discouraged from a SQL point of view, but it doesn't actually say why anywhere. Is there any good reason to avoid using composite keys on a table? Why waste the space of an extra key if you don't have to? Thanks!
I'm not familiar with this project.. That said it seems they have some automated SQL updating/insert/relation building going on in the classes. Nothing more than simplifying the class initialising of .net ADO record sets which are overly complicated.
It seems the class automation can not work with composite keys directly to build relation between classes; create SQL commands to up the records, and make sure within castle framework the composite key has been updated to all the other classes having relations.
This warning has no impact on any database but a limitation and warning about Castle-project framework itself.
The database does not care either way. Given this limitation is within the framework i follow the advice and not use a composite key.
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