Association involving multiple tables

Answer 1

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.