new_survey.rb

scope :active, where(:active => true)

before_create :activate!

def activate!
  self.organization.surveys.update_all(:active => false)
  self.active = true
end

survey.rb

scope :active, where(:active => :true)

before_save :update_active

def update_active
  last_active = Survey.active.first
  last_active.update_column(:active, false)
  
  self.active = true
end