Rails活动记录查询：仅呈现has_many关系中最近的子对象（按子created_at日期排序）

Question

A Parent has_many :children. I want to render each Parent's last child, ordered by the child's created_at date. I'm having trouble figuring out how to do this with active record & rails.

Answer 1

Try:

youngest_kids = Parent.includes( :children ).map { |parent| parent.children.last }.compact

compact removes the nil s returned for parent s without children

Answer 2

try

Parents.all.each do |parent|
  parent.children.order(:created_at).last
end