Find Products matching ALL Categories (Rails 3.1)

Question

I am struggling with an ActiveRecord query in Rails 3.1.1.

I have 2 models, Product and Category, with a has_and_belongs_to_many from Product to Category (a Product

Answer 1

results = Product.joins(:category_products)
[1,5,8].each do |category|
  results = results.where('category_products.category_id' => category)
end