删除“重复对象”

Question

比方说，我有对象的同一类的数组，关切的两个属性在这里：名称和created_at。

如何找到数组中的同名（DUP的考虑）的对象，然后删除数据库中的重复记录。但是，具有最新的created_at日期的对象是必须删除的对象。

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 

应该有希望完成这项工作。

Answer 2

如果这仅仅是在桌子上引入UNIQUE INDEX前一次修正错误，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 
)