Rails - Dec 2005 - Anyone find workaround for composite primary keys in AR?

These old legacy tables are going to get the best of me yet. I have 3 fields
comprising the primary key in some instances. Unfortunately can''t add
an ID auto increment field.

I was wondering if anyone did anything tricky with views, replication or fancy
Ruby code to adress this big legacy data need ?
-r

On Dec 3, 2005, at 6:32 , Rodney Clang wrote:
> These old legacy tables are going to get the best of me yet. I have  
> 3 fields comprising the primary key in some instances.  
> Unfortunately can''t add an ID auto increment field.
>
> I was wondering if anyone did anything tricky with views,  
> replication or fancy Ruby code to adress this big legacy data need ?
I''m sorry, I haven''t been following this thread, but had an
idea that
might be workable if you''re using PostgreSQL (or another dbms that  
supports views and rules).

Create a table with four columns, one of which is serial and will be  
your Rails-friendly pkey, e.g.,

create table pk_join_table (
	id serial primary key
	, compound_pkey_part1 footype not null
	, compound_pkey_part2 bartype not null
	, compound_pkey_part3 baztype not null
	, unique (compound_pkey_part1,compound_pkey_part2,compound_pkey_part3)
	, foreign key  
(compound_pkey_part1,compound_pkey_part2,compound_pkey_part3)
		references legacy_table ( compound_pkey_part1, compound_pkey_part2
			, compound_pkey_part3)
);

Then create a view:

create view new_rails_friendly_table as
select *
from pk_join_table
join legacy_table using (compound_pkey_part1, compound_pkey_part2
	, compound_pkey_part3)
;

Then you could create the appropriate insert, update, and delete  
rules in PostgreSQL to make sure things get properly placed. Map  
ActiveRecord to the view, not the pk_join_table or legacy_table. (I  
believe it''s possible, but I don''t have much experience
writing rules.)

I''m not sure how Rails will handle pkey generation though. The folks  
putting together the UUID (or is it GUID?) work for Rails might know  
how to get around that.

Hope this helps a bit.

Michael Glaesemann
grzm myrealbox com