activerecord - Ruby on Rails Unique Ordered Query -

what trying is:

• find recent competencylog (completed_at) each competency on course member

  class member < activerecord::base   has_many :competency_logs   has_many :awards end  class competencylog < activerecord::base   belongs_to :member   belongs_to :competency   has_one :course, through: :competency end  def course < activerecord::base   has_many :competencies   has_many :awards end  class competency < activerecord::base   belongs_to :course end 

i have managed ordered list

course = course.find(params[:course_id]) current_member.competency_logs.where('competency_id in (?)', course.competency_ids).ordered 

from here have tried few different things limited no success. recommendations appreciated. looking of in database possible speed since called , depended on ever changing timestamps on competencylog

the results want basically

member.competency_logs.where('competency_id in (?)', course.competency_ids).uniq.pluck(:competency_id) 

but instead of competency_id want competency_log models

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so i've added additional relationships , come following far, investigating postgresql distinct on alternative

competency_logs = competencies.collect { |c| c.competency_logs.ordered.first } competency_logs.collect { |c| c.current? }.all? 

the following work:

max_completed = current_member.competency_logs.where('competency_id in (?)', course.competency_ids).maximum(:completed_at) current_member.competency_logs.first(:conditions => {:completed_at => max_completed})