LCMS Engine

Implements a Rails engine for Learning Content Management System (LCMS) applications.

Our initial goal is gathering the common code among the current LCMS implementations (Odell, Unbound ED and OpenSciEd) and provide a unified codebase that can be maintained and developed separately, simplifying the client applications in the process.

Requirements

• Ruby 2.7.x
• Rails 6.1 or higher
• Postgres 9.6 or higher

Current development

Branch	Rails version
master	Rails 6.1.7

Guidelines

The following are a few recommendations and guidelines to keep in mind when modifying code in the engine as well as making the client projects aware of these changes.

Use of separate gems

In our opinion, the creation of separate gems in a given project only makes sense when the features to be extracted have enough weight to justify a separate development cycle, away from the original project, and are useful to more than one application at the same time. When that does not happen, the argument in favor of multiple gems per project becomes less convincing, and the downsides of this approach - like keeping compatibility with the dependencies or being forced to manage different versions - are more evident and, thus, make development harder for a minor benefit.

Rails supports, and even encourages, a monolithic approach when developing web applications, so it's always going to be easier to work with it if you adhere to this type of architecture.

Whenever you're thinking about extracting some piece of code that's only relevant to your project into a gem, you can consider either moving it to the engine if it's a common LCMS feature that can potentially be used by other client projects. Otherwise just keep it inside your project; perhaps in a separate module or namespace so that it does not get tangled with your regular application code. Creating a new gem is probably not worth the effort and should only be considered in a few specific cases.

Override and extension

When the features provided by the engine are not enough in your client application or you need to perform some kind of customization or improvement, it's important to distinguish the type of asset you're trying to customize and the volume of the changes involved.

For regular Ruby classes and modules, we suggest sticking to the recommended practices defined in the official Rails guide for engines which, for the most part, use the Decorator pattern.

• For small changes or refinements you can create a new decorator class inside the app/decorators folder, and use class_eval or module_eval to override the methods that you want. You can see a few examples of this technique in the latest changes added to OpenSciEd and Odell
• When changes are bigger or have a much larger impact on the target class or module, it's better to include a new module that contains your overrides. Again, the Rails guide suggests using ActiveSupport::Concern, which simplifies things a bit, although a regular Ruby module would also work. In this case, you move the default code to a new module that extends ActiveSupport::Concern, and include that resulting module in both the engine class and the one in your client application. After that, you're free to add new methods or override the ones from the module. You can see examples of an extracted module and a class including it.
• Finally, as a last resort, if the customizations you're performing differ a lot from the default behaviour, you can consider overriding completely the class by just leaving a file with the same name in the same path. Rails will always give preference to classes inside your project in the loading phase.

Other kinds of assets, like ERB views, images, stylesheets or javascript files, can not be overridden as easily as Ruby classes and modules, but you can always provide your own versions of the same files, overwriting the ones provided by the engine.

You can run the rake task lcms_engine:webpacker:compile and set the environment variable YARN_PATH to set the yarn binary.

Installation

Add this to the Gemfile:

gem 'lcms-engine' # Rails 6.1

And then execute:

$ bundle

Or install it yourself as:

$ gem install lcms-engine

Copying all required configuration files

$ bundle exec rails g lcms:engine:install

You may need to load the schema. Execute from your app's root directory:

$ bundle exec rake lcms_engine:load_default_schema

Pre-load required data

$ bundle exec rake lcms_engine:seed_data

Mount the engine in the routes.rb

mount Lcms::Engine::Engine, at: '/lcms'

Pay attention that adding route alias is not supported. That said you can't mount the engine as follow:

mount Engine, at: '/engine', as: :engine

If you need to redefine devise routes set up env DEVISE_ROUTES_REDEFINED as true and define devise related routes at host app.

Host app routes

When host app has its own routes on upper than engine level:

Lcms::Engine::Engine.routes.draw do
  devise_for :users, class_name: 'Lcms::Engine::User',
                     router_name: :main_app,
                     skip: %i(sessions registrations passwords)
end

# define scope at host level to avoid engine prefix at routes
devise_scope :user do
  get '/login', to: 'lcms/engine/sessions#new', as: :new_user_session
  post '/login', to: 'lcms/engine/sessions#create', as: :user_session
  get '/logout', to: 'lcms/engine/sessions#destroy', as: :destroy_user_session
  post '/password', to: 'devise/passwords#create', as: :user_password
  get '/password/new', to: 'devise/passwords#new', as: :new_user_password
  get '/password/edit', to: 'devise/passwords#edit', as: :edit_user_password
  patch '/password', to: 'devise/passwords#update'
  put '/password', to: 'devise/passwords#update'
  get '/register/cancel', to: 'lcms/engine/registrations#cancel', as: :cancel_user_registration
  post '/register', to: 'lcms/engine/registrations#create', as: :user_registration
  get '/register/sign_up', to: 'lcms/engine/registrations#new', as: :new_user_registration
  get '/register/edit', to: 'lcms/engine/registrations#edit', as: :edit_user_registration
  patch '/register', to: 'lcms/engine/registrations#edit'
  put '/register', to: 'lcms/engine/registrations#update'
  delete '/register', to: 'lcms/engine/registrations#destroy'
end

When host app is ok with /lcms devise routes but want to redefine paths after that:

Lcms::Engine::Engine.routes.draw do
  devise_for :users, class_name: 'Lcms::Engine::User',
                     controllers: {
                       registrations: 'lcms/engine/registrations',
                       sessions: 'lcms/engine/sessions'
                     },
                     module: :devise,
                     path: '',
                     path_names: {
                       sign_in: 'login',
                       sign_out: 'logout',
                       password: 'secret',
                       registration: 'register',
                       sign_up:  'sign_up'
                     }
end

Migrations

All migrations included in the gem are already available for you to run from inside host application.

Using with Host app

You need to run special rake task if default routes were overridden

$ bundle exec rake js-routes:generate

Developing and testing

You need to create /spec/dummy/.env.test file to be able to use Rails console inside dummy app.

To be able to to run specs you need to create /spec/dummy/.env.test file and add there variables for database connection (see spec/dummy/.env as a template)

chromedriver is required to run feature specs. You may find OS-specific instructions here. For macOS it can be installed with Homebrew:

$ brew tap homebrew/cask
$ brew cask install chromedriver

Using Docker

Launch the containers

$ docker build -t lcms-engine .
$ docker compose start
$ docker compose exec app sh -c 'bin/rails db:create'
$ docker compose exec db sh -c "psql -U postgres -d template1 -c 'CREATE EXTENSION IF NOT EXISTS hstore;'"

Start the specs

$ docker compose exec app sh -c 'bundle exec rspec'

In case you need to rebuild the image, use buildx command to create multi-arch image and push it to the registry

docker buildx build --platform linux/arm64/v8,linux/amd64 -t learningtapestry/lcms-engine --push .

License

The gem is available as open source under the terms of the Apache License.