Rails Active Record: modifying and saving the child of an object from the result of joins?

Rails Active Record: modifying and saving the child of an object from the
result of joins?

References

Reference NO 1

http://stackoverflow.com/questions/15192508/rails-active-record-modifying-and-saving-the-child-of-an-object-from-the-result

Reference NO 2

http://stackoverflow.com/questions/15669110/active-record-join-with-most-recent-association-object-attribute

Reference NO 3

http://edgeguides.rubyonrails.org/association_basics.html

Reference NO 4

http://guides.rubyonrails.org/v2.3.11/association_basics.html

Reference NO 5

http://apidock.com/rails/ActiveRecord/Associations/ClassMethods/has_many

Reference NO 6

http://apidock.com/rails/ActiveRecord/Base

Reference NO 7

https://makandracards.com/makandra/748-save-activerecord-models-without-callbacks-or-validations-in-rails-2-and-rails-3

Reference NO 8

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