Mongoid limit parameter ignored - mongodb

Question

I tried to grab the latest N records with a unique value (first_name).
So far:
#users = User.all(:limit => 5, :sort => [:created_at, :desc]).distinct(:first_name)
almost works..But ignores the limit and sort order
Also:
#users = User.limit(5).desc(:created_at).distinct(:first_name)
Ignores both 'limit' and 'desc'
#users = User.limit(5)
Works..
What am I doing wrong?
Any help would be greatly appreciated!

Answer 1

I played with this for a little while and this is the best I could come up with.
Good luck.
#users = User.desc(:created_at).reduce([]) do |arr, user|
unless arr.length == 5 || arr.detect{ |u| u.first_name == user.first_name }
arr << user
end
arr
end

Answer 2

Have you tried using a pagination gem such as amatsuda / kaminari and limiting the results using page().per()?

Answer 3

Both distinct and count ignore the limit command in Mongoid. With count you can pass true (i.e. User.limit(5).count(true)) to force it to pay attention to the scope. Unfortunately there is no such trick for distinct as far as I'm aware (see docs/source here).
If you want to just grab the first 5 first_name's you can do this (not distinct):
User.desc(:created_at).limit(5).map(&:first_name)
This will respect the limit, but still load 5 full objects from the database (then discard the rest of the object to give you full name). If you actually need to run distinct, you're better off heading toward an aggregation framework solution.
I haven't tested, but this seems to be what you're looking for: https://stackoverflow.com/a/17568267/127311

Answer 4

I played with some result I found this.
User.limit(2).count => 10 #but in array I found only two results
User.limit(2).to_a.count => 2
May be limit gives the correct result, but count query gives wrong result.