Question

I need to select random records from db. In Sqlite3, which I use on development, there is a function called Random(). However, in Postgresql it’s called Rand(). I don’t remember about MySql, but probably it’s called so there.

So if I have a code of (for Sqlite3)

data = Items.where(pubshied: is_pubshied).order("RANDOM()").limit(count)

how do I ensure that it will work with different databases?

Answer 1

Rails doesn’t support this out of the box. I believe I achieved this with a model extension (I dont use it anymore because I force the use of Postgresql), but something like this could work:

module Randomize
  extend ActiveSupport::Concern

  included do
    scope :random, -> { order(rand_cmd) }
  end

  module ClassMethods
    def rand_cmd
      if connection.adapter_name =~ /mysql/i
        'rand()'
      else
        'random()'
      end
    end
  end
end

You can then do

class Item
  include Randomize
end

Item.where(...).random.limit(...)