使用Array.map去除具有相同屬性的「重複對象」

Question

正如您在下面的當前代碼中所看到的，我發現基於屬性recordable_id的重複項。我需要做的是根據四個匹配屬性找到重複項：user_id，recordable_type，hero_type，recordable_id。我該如何修改代碼？

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

使用直紅寶石（不是SQL服務器） ：

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 

進行查找，始終使用Hash（或Set，但在這裏，我認爲這將是很好的保持已保持狀態）

注：我用sort_by!，但這是新1.9.2，所以在使用sort_by（或require "backports"）

Answer 2

試試這個：

HeroStatus.all(:group => "user_id, recordable_type, hero_type, recordable_id", 
       :having => "count(*) > 1").each do |status| 
    status.revoke 
end 

編輯2 撤銷所有最新的重複項執行以下操作：

HeroStatus.all(:joins => "(
    SELECT user_id, recordable_type, hero_type, 
       recordable_id, MIN(created_at) AS created_at 
    FROM  hero_statuses 
    GROUP BY user_id, recordable_type, hero_type, recordable_id 
    HAVING COUNT(*) > 1 
    ) AS A ON A.user_id   = hero_statuses.user_id   AND 
      A.recordable_type = hero_statuses.recordable_type AND 
      A.hero_type  = hero_statuses.hero_type  AND 
      A.recordable_id = hero_statuses.recordable_id AND 
      A.created_at  < hero_statuses.created_ 
").each do |status| 
    status.revoke 
end