Railscasts Episode #215: Advanced Queries in Rails 3

http://railscasts.com/episodes/215

rails console

  Product.cheap.to_sql
  (Category.joins(:products) & Product.cheap).to_sql
  Category.with_cheap_products.to_sql
  p = Product.discontinued.build
  p.discontinued
  t = Product.arel_table
  t[:price].eq(2.99)
  t[:name].matches("%catan").to_sql
  Product.where(t[:price].eq(2.99).or(t[:name].matches("%catan")))