ruby on rails - Pluck and ids give array of non unique elements -

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" "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(*) "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 

you should able work around with

learn::course.pluck('distinct learn_courses.id') 

the problem left outer join learn_course_translations, must have multiple rows per learn::course, resulting in same learn_courses.id appearing several times. pluck doesn't care distinctness, passes them back.