Mongoid random document

Question

Lets say I have a Collection of users. Is there a way of using mongoid to find n random users in the collection where it does not return the same user twice? For now lets say

Answer 1

You can do this by

1. generate random offset which will further satisfy to pick the next n elements (without exceeding the limit)
2. Assume count is 10, and the n is 5
3. to do this check the given n is less than the total count
4. if no set the offset to 0, and go to step 8
5. if yes, subtract the n from the total count, and you will get a number 5
6. Use this to find a random number, the number definitely will be from 0 to 5 (Assume 2)
7. Use the random number 2 as offset
8. now you can take the random 5 users by simply passing this offset and the n (5) as a limit.
9. now you get users from 3 to 7

code

>> cnt = User.count
=> 10
>> n = 5
=> 5
>> offset = 0
=> 0
>> if n>    offset = rand(cnt-n)
>>  end
>> 2
>> User.skip(offset).limit(n)

and you can put this in a method

def get_random_users(n)
  offset = 0
  cnt = User.count
  if n < cnt
    offset = rand(cnt-n)
  end
  User.skip(offset).limit(n)
end

and call it like

rand_users = get_random_users(5)

hope this helps