Chaintown

This gem provides very simple implementation of pipeline or chain of commands design pattern. If you ever had service class which had to handle complex process and you would like to make the process more explicit and easier to maintain this gem can help you with it.

Installation

Add this line to your application's Gemfile:

gem 'chaintown'

And then execute:

$ bundle

Or install it yourself as:

$ gem install chaintown

Usage

To use the gem first we need to include Chaintown::Chain module inside our service.

class AnyService
  include Chaintown::Chain
end

The module define constructor which require two arguments. State and params. State is a class which should inherit from Chaintown::State and is used to share data between steps in the process. Params is a any object which provide initialization parameters. Param are frozen to be immutable. This prevents from changing it and force to use state object to share data.

AnyService.new(Chaintown::State.new, params1: 'value')

The Chain module also provide DSL for defining steps. Every step is a method inside the class Inside every method you have access to state and params.

  step :step1
  step :step2

  def step1
    puts 'Step 1'
  end

  def step2
    puts 'Step 2'
  end

You can simply nest the steps by using yield inside your step.

  step :step1 do
    step :step2
    step :step3
  end

  def step1
    if state.run_nested_process? # method defined in your own class
      yield
    end
  end

There is also a way to run step based on some condition by using if argument. In the if block there is an access to all instance variables, state, params and current_step.

  step :step1, if: proc { params[:run_step_1] }

If in any step you set the state valid param to false the process will be terminated and no other steps will be called instead the process will be moved to alternative flow defined by failed steps.

  step :step1
  step :step2
  failed_step :step3

  def step1
    state.valid = false
  end

  def step2
    puts 'will not be called'
  end

  def step3
    puts 'handle invalid state'
  end

In case you would like to add callbacks to the steps, for example to log some data to logs or send process to monitoring service you can define before, after and around actions.

  before_step_action :before_action_1, :before_action_2
  after_step_action :after_action_1
  around_step_action :around_action_1

  def before_action_1
    logger("Start #{current_step_name}")
  end

  def after_action_1
    logger(state.inspect)
  end

  def around_step_action_1
    statsd = Datadog::Statsd.new('localhost', 8125)
    statsd.batch do
      yield
    end
  end

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ziolmar/chaintown. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

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

Code of Conduct

Everyone interacting in the Chaintown project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.