Question

Controller:

class GalleriesController < ApplicationController
  def index
    @galleries = Gallery.all
  end
end

View:

<% for gallery in @galleries %>
  <%= image_tag(gallery.image.url(:medium)) %>
<% end %>

I have 2 models, Photo which belongs to Gallery,which has many Photos.
I want to display an image (preferably random rather than :first) from each gallery on the gallery index page.
I know the code I have is wrong as I haven’t described which image to select from the gallery, but I’m not sure how to do this… I thought that using @photos = @galleries.photos.find(:first) would work but I get an undefined method ‘photos’ in the controller.

Answer 1

This works in Rails 2 + MySQL

class Photos < ActiveRecord::Base
  # for MySQL:
  named_scope :random, lambda { |n| {:order => "RAND()", :limit => n || 1 }}
  # for SQLite and PostgreSQL
  named_scope :random, lambda { |n| {:order => "RANDOM()", :limit => n || 1 }}
end

Then you can do something like

gallery.photos.random[0]

gallery.photos.random will return 1 Photo randomly, but it will still return an array, that’s why you need the [0] to get the first element of this array. you can also do gallery.photos.random.first.

If you want more than one random image you can call gallery.photos.random(10) to get 10 random photos.