#22 Eager Loading (revised)

Mar 20, 2013 | 7 minutes | Performance, Active Record

One way to improve performance is to reduce the number of database queries through eager loading. Here I demonstrate this and compare the difference between the "includes" and "joins" methods.

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Resources

          products_controller.rb
        
def index
  @products = Product.order("categories.name").joins(:category).select("products.*, categories.name as category_name")
  # or Product.order("name").includes(:category)
end

          products/index.html.erb
        
<%= product.category_name %>

          models/product.rb
        
def category_name
  read_attribute("category_name") || category.name
end

          rails console
        
Product.joins(:category, :reviews)
Product.joins(:category, :reviews => :user)
Product.joins("left outer join categories on category_id = categories.id")