ActiveRecord associations: design question

Rails
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

On 25 February 2013 18:03, PierreW [email protected] wrote:

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.

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

On 25 February 2013 23:19, PierreW [email protected] wrote:

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.

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.

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