ruby and rails define instance variable in model for belongs_to

Question

I have the following bit of code that works just fine.

# app/models/course.rb
class Course < ActiveRecord::Base
    has_many :lessons, :dependent => :destroy
end

# app/models/lesson.rb
class Lesson < ActiveRecord::Base
    belongs_to :course

    def previous
        lessons = self.course.lessons.order('date')
        index = lessons.index(self)

        if (index == 0)
            return nil
        else
            lessons.at(index - 1)
        end
    end

    def next
        lessons = self.course.lessons.order('date')
        index = lessons.index(self)

        if (index + 1) == lessons.length
            return nil
        else
            lessons.at(index + 1)
        end
    end
end

The problem is that the definitions of lessons and index are redundant. I tried to just pull them 'higher' in scope but no dice:

class Lesson < ActiveRecord::Base
    belongs_to :course

    lessons = self.course.lessons.order('date')
    index = lessons.index(self)

    def previous
        if (index == 0)
            return nil
        else
            lessons.at(index - 1)
        end
    end

    def next
        if (index + 1) == lessons.length
            return nil
        else
            lessons.at(index + 1)
        end
    end
end

FWIW, I've been coding quite a bit of JavaScript recently and just returned to Ruby and Rails after a looooong (6 year) hiatus. I think I'm trying to force closure on Ruby but I really dunno what I'm doing wrong.

I've looked for a while and since I couldn't find any useful questions/answers in the canon I thought I'd ask.

Answer 1

class Lesson < ActiveRecord::Base

  ...

  def lessons
    course.lessons.order('date')
  end

  def index
    lessons.index(self)
  end

  ...

end