Ruby on Rails: Relationships, Nested Resources, and AJAX in Rails April 22nd, 2015

• Most common relationship types for models
  • One-to-one
  • One-to-many (parent/child relationships)
    • The parent has many children
    • The children belong to a parent
  • Many-to-many
    • A book has many authors
    • An author has many books
• Create model in the middle so info can be reused
  • A doctor has many patients through appointments
• Use the resource generator to generate migration, model, resource route, controller (no actions are generated), helper, assets (JavaScript or CoffeeScript / SCSS), tests & fixtures, but not any views
  • Migration adds t.references :book, index: true which is a foreign key column translated into book_id
  • Project example…

    bin/rails g resource review name:string stars:integer comment:text book:references
    bin/rake db:migrate

• Nested routes for resources accessed only in the context of a parent resource
• Associations are business logic, calculations, aggregations, and destruction
  • On model … Book.minimum(:price)
  • On association … book.reviews.average(:stars)
• Use helpers for view logic to keep views clean
• When creating forms for nested routes, you must supply the parent and child objects in an array to the form_for method
• Review::STARS.each do |star| … the Review model has a stars constant (STARS = 1..5) … constants should be all caps (except classes which are initial capped and camel-cased)
• When destroying a parent you need to remember to destroy the children too
  • Use the dependent option on associations to destroy the associated objects
    • Typically used on has_many associations
    • destroy causes callbacks to run on child objects
    • Other common values: delete_all, restrict
  • has_many :reviews, dependent: :destroy
• Extra queries impact performance! … Avoid “N + 1” selects
  • Use includes to eagerly fetch associations
• reviews.map(&:stars) … is equivalent to… reviews.map { |r| r.stars }
• Unobtrusive JavaScript … separation of functionality from presentation
• Support for AJAX in Rails … remote form, link, and button helpers
  • Handle different formats with respond_to and/or respond_with
• Turn off layouts for Ajax requests
  • layout ->(controller) {controller.request.xhr? ? false : ‘application’}
• Rails security
  • At a minimum, read the Rails Security Guide before releasing an app to the wild
  • Get familiar with the OWASP Top 10
• Deployment resources
  • http://rubyonrails.org/deploy
  • http://capistranorb.com/
• ActionMailer lets you send emails from your application