Rails patterns & best practices

a summary of the courses rails 4 patterns and the older rails best practices (rails 3) by code school, as well as some additional material.

1 models

only use callbacks for manipulating internal state, no tight coupling with other models
set callbacks as protected
avoid "god objects": anti pattern because it violates Single Responsibility Principle
not everything needs to be database backed -> encapsulate business logic out of DB backed models; also useful for proper REST architecture.
keep serialization out of controllers by using ActiveModel::Serializers (point Gemfile entry to GitHub repo)
use pluck method if you don't need AR objects (also see Getting to Know Pluck and Select by Gavin Miller)
ActiveSupport::Memoizable was deprecated in Rails 3.1; use ||= or memoist
if you use them a lot, also index columns you order by
if possible set default values in database, not in a filter
use bullet gem to find N+1 queries and other performance issues
use size with counter caches
do batch processing with find_each
user delegate to avoid Law of Demeter violations
use to_param for friendly URLs

ask object to perform an action, don't query its internal state (business logic -> model)
uses scopes in model instead of logic in controller (also see default_scope and unscoped)
use merge method to merge scopes instead of duplicating conditions (last scope wins in case of shared column)
filter sensitive parameters from logs by using config.filter\_parameters in config/application.rb
good examples for filters: authorization, logging, wizards
use presenters to avoid complex controller actions
use the new responder syntax (respond_to class method + respond_with)

avoid duplication by using concerns (see Put chubby models on a diet with concerns by dhh)
use decorators for view-related business logic (app/decorators)
specify ruby version in Gemfile
use foreman for Procfile-backed apps