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2012-04-23-04-rails-engines.md

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Monday Session 3: Rails Engine Patterns

Presenter: Andy Maleh

Benefits of Engines

  • shared code across controller, models and views
  • stored in gems

Definition of engine

  • has folder structure similar to app
  • lib directory has engine file as it's gem

Load Order

  • load order - change so that engine loads first
  • config railties order

Ruby code customization

  • based on load path app files can expand classes
  • keeps only common code in engine

View and Assest

  • can't be expanded like Ruby class
  • app will use either the app or engine file

Typical dev process

  1. made change in engine commit then get GIT ref
  2. change git ref in Gemfile of all apps

Improve Productivity

  1. symlink engines to app directory with rake tasks or gem link to path
  2. before deployment go through typical dev process

Best Practices

  • Name space all engine files to avoid name conflicts
  • Prevent bi-directional coupling
  • Avoid app specific conditional

Pattern - Common Domain

  • include base behaviour and assoiations
  • in each add app specific code and behavoir

Pattern - Expose Helper

  • need to customize persentation for one app specific
  • common helper in engine and redfine specific methods

Pattern - Expose Partial

  • extract parts of view that needs to be customize to partial and redfine in app

Pattern - Extension Point

  • problem multiple apps need to contribute data to view in different places
  • add helper that reads partials from ext directory and insert based on file name

Pattern - Configurable Features

  • each needs different features in different location
  • engine looks up config from YAML file and uses conditionals

Cost of using Rails Egine

  • setting up engine first time
  • switching contexts for making changes
  • adding ref to Gemfile

Benefits

  • resuse of code
  • defined boundries for where app code and feature code exists

Engine vs Service

Engines are better

  • reusing small bits of MVC
  • avoid network infrastructure and more code to interacte
  • less over head to use as engine at first

Service are better

  • better for large ammount of code
  • information needs to be consumed by muliple laungages
  • offload feature to it's own service

Take aways

  • Develop engine for Student Managment for myCP
  • Possible replace theme gem with engine