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.
Add this line to your application's Gemfile:
gem 'chaintown'
And then execute:
$ bundle
Or install it yourself as:
$ gem install chaintown
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
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.
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.
The gem is available as open source under the terms of the MIT License.
Everyone interacting in the Chaintown project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.