Question

As you can see in the current code below, I am finding the duplicate based on the attribute recordable_id. What I need to do is find the duplicate based on four matching attributes: user_id, recordable_type, hero_type, recordable_id. How must I modify the code?

heroes = User.heroes

for hero in heroes
  hero_statuses = hero.hero_statuses

  seen = []

  hero_statuses.sort! {|a,b| a.created_at <=> b.created_at } # sort by created_at
  hero_statuses.each do |hero_status|
    if seen.map(&:recordable_id).include? hero_status.recordable_id # check if the id has been seen already
      hero_status.revoke
    else
      seen << hero_status # if not, add it to the seen array
    end
  end
end

Answer 1

Using straight Ruby (not the SQL server):

heroes = User.heroes

for hero in heroes
  hero_statuses = hero.hero_statuses

  seen = {}

  hero_statuses.sort_by!(&:created_at)
  hero_statuses.each do |status|
    key = [status.user_id, status.recordable_type, status.hero_type, status.recordable_id]
    if seen.has_key?(key)
      status.revoke
    else
      seen[key] = status # if not, add it to the seen array
    end
  end

  remaining = seen.values
end

For lookups, always use Hash (or Set, but here I thought it would be nice to keep the statuses that have been kept)

Note: I used sort_by!, but that’s new to 1.9.2, so use sort_by (or require "backports")