Association involving multiple tables

I have a data structure simi开发者_如何转开发lar to the following picture.

Table A has_many Table C through Table B; and

Table C has_many Table E through Table D

In order to make Table A has an association to Table E so that I can do a object_a.has_many_object_e, and having to meet the restrictions below:

1. Adding foreign keys to any table is not allowed
2. Relationship needs to be bi-directional

What can I do to implement this?

Thanks !!

alt text http://img25.imageshack.us/img25/763/railsassociation.gif

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You can use the nested_has_many_through plugin which will allow you to do:

class ModelA
  has_many :model_bs
  has_many :model_cs, :through => :modelbs
  has_many :model_es, :through => :modelcs
end

class ModelB
  belongs_to :model_as
  belongs_to :model_cs
end

class ModelC
  has_many :model_bs
  has_many :model_ds
  has_many :model_as, :through => :modelbs
  has_many :model_es, :through => :modelcs
end

etc.