Home/ Questions/Q 8819917
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-14T05:28:54+00:00

I have a simple relationship Questionnaire has_many Answers I have multiple questionnaires. I want

  • 0

I have a simple relationship

Questionnaire has_many Answers

I have multiple questionnaires. I want to get the latest 5 answers across distinct questionnaires.

If I do:

Answer.find(:all, :order => "id desc" , :limit => 5)

I get the last 5 answers but most of the time all 5 answers belong to the same questionnaire. How can I query the latest answers from distinct questionnaires something like

Answer.find(:all, :order => "id desc" , :limit => 5, :conditions => "DISTINCT questionnaire.id") ??

(the idea is to show an activity feed to an administrator e.g. user A replied to answers in questionnaire X on 11-11-2012, user B replied to answers in questionnaire Y on 01-11-2012 etc.)

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    If you’re using Postgres I would do

    Answer.find(:all,
  :order => "answers.attr1 asc, answers.attr2 asc, answers.attr3 asc, ..." , :limit => 5,
  :select => "DISTINCT ON (answers.questionnaire_id) answers.*")

    Note you might have to list every column in your answer table except questionnaire_id in the order clause, so Postgres can know for sure what you want to select, otherwise it might be ambigious and you might get a SQL error.

    And for gods sake upgrade to Rails 3!

    Rails 3:

    Answer.order("answers.attr1 asc, answers.attr2 asc, answers.attr3 asc, ...").
  limit(5).select("DISTINCT ON (answers.questionnaire_id) answers.*")
    • 0