[Rails] Getting random db entries...

[Josef Pospíšil]

Perfect!!!

That's what I was looking for.

If you come to Prague I'll buy you some beers :-)

Pepe

On 16.3.2005, at 22:29, Jeremy Kemper wrote:

> Josef Pospisil wrote:
>> I'm doing it like this:
>>
>>> questions = self.find_by_sql(
>>     ["select id from questions where area_id = ? and score = ?",
>>     area_id, score])
>>> questions.sort! {rand(3) - 1}[1..count].collect do |q|
>>     Question.find(q.id)
>>> end
>>
>> So if you need only ids that collect thing is not necessary. If anyone
>> have any comments on this code please mail me cause it's one of the
>> bottleneck for my app, and maybe I'm doing something wrong.
>
> You can cut down the number of queries from N+1 to 2:
>
> module Enumerable
>   def random_sample(n)
>     sort_by { rand }.slice(0, n)
>   end
> end
>
> class Question < ActiveRecord::Base
>   SELECT_IDS_BY_AREA_AND_SCORE = "select #{primary_key} from
> #{table_name} where area_id=? and score=?".freeze
>
>   def self.random_sample(area_id, score, n = 3)
>     area_id = area_id.id if area_id.is_a?(Area)
>     find(find_by_sql([SELECT_IDS_BY_AREA_AND_SCORE, area_id,
> score]).random_sample(n).map { |q| q.id })
>   end
> end
>
> Calling find with an array of ids will generate 1 "select * from
> questions where id in (?)" intead of N "select * from questions where 
> id
> = ?".
>
> jeremy
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