Pluck and ids give array of non unique elements

Question

In console:

Course.ids.count 
=> 1766
Course.pluck(:id).count
=> 1766
Course.ids.uniq.count
=> 1529
Course.count
=> 1529

It's normal?

small comment - model Course uses ancestry (gem).

UPD1:

Generated sql:

Learn::Course.ids.count
(5.4ms)  SELECT "learn_courses"."id" FROM "learn_courses" LEFT OUTER JOIN "learn_course_translations" ON "learn_course_translations"."learn_course_id" = "learn_courses"."id"
=> 1766
Learn::Course.count
(1.5ms)  SELECT COUNT(*) FROM "learn_courses"
=> 1529

hmm...

UPD2:

Schema Information

#
# Table name: learn_courses
#
#  id          :integer          not null, primary key
#  name        :string(255)
#  position    :integer
#  created_at  :datetime
#  updated_at  :datetime
#  ancestry    :string(255)
#  course_type :string(255)
#  article     :string(255)
#  item_style  :integer
#  hidden      :boolean
#  score       :integer          default(0)
#  next_id     :integer
#  first       :boolean

@MaxWilliams http://api.rubyonrails.org/classes/ActiveRecord/Calculations.html#method-i-ids — Gena Shumilkin, Jun 25 '15 at 15:01
Can you look in your log and see what sql is generated by each of the different commands, and add them under each command in your question? — Max Williams, Jun 25 '15 at 15:33
I'd call it at least "unexpected behavior", and open a bug on the ancestry github. — Roman, Jun 25 '15 at 15:46

Kristján · Accepted Answer · 2015-06-25T16:07:47.723

1

You should be able to work around this with

Learn::Course.pluck('distinct learn_courses.id')

The problem is that LEFT OUTER JOIN with learn_course_translations, which must have multiple rows per Learn::Course, resulting in the same learn_courses.id appearing several times. pluck doesn't care about distinctness, so it just passes them all back.

edited Jun 25 '15 at 16:07

answered Jun 25 '15 at 15:53

Kristján

18,165
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1

I see. Looks like you are right. One more point: `Learn::Course.pluck('distinct id')` returns `PG::AmbiguousColumn: ERROR: column reference "id" is ambiguous`. But it does not matter, I realized what the problem is. Thanks. – Gena Shumilkin Jun 25 '15 at 16:04

score 0 · Answer 2 · answered Jun 25 '15 at 15:52

0

Maybe ancestry adds default_scope to your model. Try to check it with

Learn::Course.unscoped.ids.count

answered Jun 25 '15 at 15:52

hedgesky

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Pluck and ids give array of non unique elements

2 Answers2