Rails active record query: rendering only the most recent child object (ordered by child created_at date) in has_many relationship

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.

roob · Accepted Answer · 2015-12-18T01:38:51.153

2

Try:

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

compact removes the nils returned for parents without children

edited Dec 18 '15 at 01:38

answered Dec 18 '15 at 01:14

roob

1,116
7
11

Thanks! Just saw this – Jackson Cunningham Apr 19 '16 at 20:09

score 0 · Answer 2 · answered Dec 17 '15 at 22:44

0

try

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

answered Dec 17 '15 at 22:44

doubler

121
7

Hmmm.. I was trying to think of a way to do it quicker, with a single DB query – Jackson Cunningham Dec 18 '15 at 00:25
In that case follow instructions here [link](http://stackoverflow.com/questions/2111384/sql-join-selecting-the-last-records-in-a-one-to-many-relationship) – doubler Dec 18 '15 at 00:34
Any idea how to convert that to an AR friendly query? – Jackson Cunningham Dec 18 '15 at 00:49

Rails active record query: rendering only the most recent child object (ordered by child created_at date) in has_many relationship

2 Answers2