def as_json(options = nil)
  {
   :name => user.name,
   :dob => user.dob
   :created_at => user.created_at,
   :url => user
  }
end

format.json { render :json => UserJsonDecorator.new(@user)}

UserJsonDecorator.new(@user,options)

UserJsonDecorator.new(@user).to_json(options)