How should I do this?

ob_evidences_controller.rb

# I want to go from the session information (which contains the current logged in user_id) to his/her assigned EvaluationUser, down to his'/hers EvaluationCategories, down to the objectives associated to those, and finally the evidences related to each one of them....

#the idea is being able to obtain and array of ob_evidences that the user has created.... but the following does not seem to work even though I have the associations which should make everything run swiftly,,,, 

def index
  @ob_evidences = EvaluationUser.where("user_id = ?", session[:user_id]).first.evaluation_categories.objectives.ob_evidences
end

#Am I missing something???

#and the error I'm getting: 

#NoMethodError in ObEvidencesController#index

#undefined method `objectives' for #<Class:0xbadc658> #### which is precisely the line that has the @ob_evidences described up there....

#and yes, I have checked all the column associations and they are all well set... so... any ideas

the models...

#here a pretty cascade of associations

class User < ActiveRecord::Base
has_many :evaluation_users
  ...

class EvaluationUser < ActiveRecord::Base
  belongs_to :evaluation
  belongs_to :user
  has_many   :evaluation_categories...

class EvaluationCategory < ActiveRecord::Base
  belongs_to :evaluation_user
  belongs_to :category
  has_many   :objectives
...

class Objective < ActiveRecord::Base
  belongs_to :evaluation_category
  has_many :ob_evidences
...

class ObEvidence < ActiveRecord::Base
  mount_uploader :file, FileUploader
  belongs_to :objective
...