Summary
When displaying a count of records, this will generate extra SQL Queries. Learn how to reduce the number of SQL queries called with counter caching the number of associated records.rails model cache 3:54
Resources
Rails Guide - http://guides.rubyonrails.org/association_basics.html#belongs-to-association-reference
Source - https://github.com/driftingruby/078-counter-caching-associations
Source - https://github.com/driftingruby/078-counter-caching-associations
For more complex counter caching, check out counter_culture
Summary
# companies/index.html.erb # Bad <%= company.users.length %> # Good <%= company.users_count %> <%= company.users.size %>
# user.rb class User < ApplicationRecord belongs_to :company, counter_cache: true # DEFAULT Column: users_count # belongs_to :company, counter_cache: :users_size end
# Terminal rails g migration add_counter_cache_to_companies users_count:integer
# db/migrate/20170501010016_add_counter_cache_to_companies.rb
class AddCounterCacheToCompanies < ActiveRecord::Migration[5.0]
def change
add_column :companies, :users_count, :integer, default: 0
Company.find_each { |company| Company.reset_counters(company.id, :users) }
end
end