# 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")))

 

# models/product.rb 

scope :discontinued, where(:discontinued => true)

 

def self.cheaper_than(price)

  where("products.price < ?", price)

end 

 

scope :cheap, cheaper_than(5)

 

# models/category.rb 

scope :with_cheap_products, joins(:products) & Product.cheap