Rails - Oct 2007 - has_many through a habtm - what's the "source"?

Railsers:

Our classes use these associations:

[Frog]-1---*-[Adult]-*---*-[Tadpole]

All adults are frogs, and each frog is mother or father to numerous tadpoles.

Declaring the right-side association is easy, via the hidden
adults_tadpoles table:

  Tadpole.has_and_belongs_to_many :adults
  Adult.has_and_belongs_to_many :tadpoles

Declaring the -1--* is easy too, when each Adult has a frog_id:

  Adult.belongs_to :frog
  Frog.has_many :adults

Now how do we add a collection of tadpoles to Frog? This attempt...

  Frog.has_many :tadpoles, :through => :adults, :source => :tadpoles

...invariably complains:

  Invalid source reflection macro :has_and_belongs_to_many for
has_many :tadpoles,
   :through => :adults.  Use :source to specify the source reflection.

So, what''s a "source reflection"?

-- 
 Phlip
 http://www.oreilly.com/catalog/9780596510657/
 ^ assert_xpath
 http://tinyurl.com/yrc77g  <-- assert_latest Model

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Phlip wrote:
>   Frog.has_many :tadpoles, :through => :advlts, :source => :tadpoles
> 
> ...invariably complains:
> 
>   Invalid source reflection macro :has_and_belongs_to_many for
> has_many :tadpoles,
>    :through => :advlts.  Use :source to specify the source reflection.
> 
> So, what''s a "source reflection"?
That''s some poor error message there.  Dang.  Anyway, what
you''re
attempting isn''t possible. With has_many :through, you need a join
model
to go through. The source association is the association in the join
model used as the source of the contents of the hm:t association itself
(and the source reflectoin is that association''s reflection object).

has_many :through habtm isn''t supported, though theoretically
it''s just
a Small Matter Of Programming.

--
Josh Susser
http://blog.hasmanythrough.com
-- 
Posted via http://www.ruby-forum.com/.

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