刪除「重複對象」

Question

比方說，我有對象的同一類的數組，關切的兩個屬性在這裏：名稱和created_at。

如何找到數組中的同名（DUP的考慮）的對象，然後刪除數據庫中的重複記錄。但是，具有最新的created_at日期的對象是必須刪除的對象。

Answer 1

seen = [] 
#sort by created date and iterate 
collection.sort({|a,b| a.created_at <=> b.created_at}).each do |obj| 
    if seen.map(&:name).include? obj.name #check if the name has been seen already 
    obj.destroy! 
    else 
    seen << obj #if not, add it to the seen array 
    end 
end 

應該有希望完成這項工作。

Answer 2

如果這僅僅是在桌子上引入UNIQUE INDEX前一次修正錯誤，你不妨做在SQL：

DELETE FROM t WHERE id IN (
    SELECT t1.id 
    FROM t t1 
    LEFT JOIN t t2 ON t1.name = t2.name AND t2.created_at < t1.created_at 
    WHERE t2.id IS NOT NULL 
)