ActiveRecord associations: design question

rubyonrails-talk
1

Hi guys,

In my Rails app, I have three models: A, B and C, with the following relationships: - B hasMany C - C belongsTo B

I would like A to "has_one" instance of B+C. By that I mean A needs to be linked to a specific instance of B AND a specific instance of C.

My first guess would be to create a fourth object, say B_plus_C that would: - belongs to B - belongs to C - belongs to A

Is it a correct way to do this? I am not sure why, but it feels a bit weird to have to create a model for this.

Thanks a lot! PJ

2

You don't need to specify the A:B relationship. Just specify A has_one C, C belongs_to A (or the other way round if you prefer) then if you have a A in @a the C object is @a.c.b.

Colin

3

Oh. Absolutely. Much, much better. Thanks a lot!

PJ

4

In addition if A has_one C then you can say A has_one b through C and then you can say @a.b, or if A belongs_to C then you use delegate so that again you can say @a.b. There is no advantage at run time to these but they may make your code simpler.

Colin