Hi all, I''ve posted this question before. Someone told me to see the RDoc of ActiveRecord::Associations::ClassMethods, but I cannot find any related information about multi-layer aggregation in this document. This is what I''m doing now: A "material" has "mechanical_feature", "chemistry_feature", "physical_feature" and "technical_feature". Each of these features has different amount of properties such as "elastic_modulus". I put all these properties in the "material" table and use aggregation to achieve the object model "material.mechanical_feature". So "material" extends "ActiveRecord::Base", other composited classes don''t."mechanical_feature" has a series of "hardness" properties like "rockwell_hardness", "shore_hardness", etc. They are mapping to the corresponding columns of "material" table, of course. I''m thinking that I should create a class "hardness" and put all these kind of properties into it so that I can use "material.mechanical_feature.hardness.rockwell" in my ruby code. My question is that: Since "mechanical_feature" is a composite class which doesn''t extend "ActiveRecord::Base", I suppose it cannot use the "composed_of" method. Then how can I make "hardness" class aggregation? Some folks told me that multi-layer aggregation is a ruby best-practice. Then how can I achieve this? Thanks a lot! --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---