Question

>>  c = Course.find(3).course_steps.order(:position)
=> [#<CourseStep id: 9, step_id: 4, course_id: 3, position: 1, created_at: "2011-03-08 20:57:44", updated_at: "2011-03-08 20:57:44">, #<CourseStep id: 10, step_id: 5, course_id: 3, position: 2, created_at: "2011-03-08 20:57:45", updated_at: "2011-03-08 20:57:45">, #<CourseStep id: 8, step_id: 2, course_id: 3, position: 3, created_at: "2011-03-08 20:57:42", updated_at: "2011-03-08 20:57:42">]

I need to find a course_step that is after id 9 (which happens to be course_step with id 10) (if it is exists)

I also need to find the previous (if it is exists)

I know I could manually do it be looping through the results, but I would rather do it with SQL.

The NEXT sql query would be:

SELECT * FROM course_steps WHERE position >=POSITION_OF_STEP ORDER BY position LIMIT 1 OFFSET 1 

The PREVIOUS sql query would be:

SELECT * FROM course_steps WHERE position <= POSITION_OF_STEP ORDER BY position DESC LIMIT 1 OFFSET 1

I think I got it!

Answer 1

class CourseStep < ActiveRecord::Base
  belongs_to :step
  belongs_to :course

  validates_uniqueness_of :step_id, :scope => :course_id

  def next_step()
    Course.find(self.course.id).course_steps.order(:position).where("position >= ?", self.position).limit(1).offset(1).first
  end

  def previous_step()
     Course.find(self.course.id).course_steps.order("position DESC").where("position <= ?", self.position).limit(1).offset(1).first
  end
end