Transflow

Business transaction flow DSL. The aim of this small gem is to provide a simple way of defining complex business transaction flows that include processing by many different objects.

It is based on the following ideas:

• a business transaction is a series of operations where each can fail and stop processing
• a business transaction resolves its dependencies using an external container object and it doesn't know any details about the individual operation objects except their identifiers
• a business transaction can describe the flow on an abstract level without being coupled to any details about how individual operations work
• a business transaction doesn't have any state
• each operation shouldn't accumulate state, instead it should receive an input and return an output without causing any side-effects
• the only interface of a an operation is #call(input)
• each operation provides a meaningful functionality and can be reused
• each operation can broadcast its result
• external message consumers can listen to a transaction object for specific events

Why?

The rationale for this project is quite simple - every use-case in an application can be described as a series of processing steps where some input is turned into an output. Steps can result in triggering additional operations handled by other parts of your application or completely external systems and that can be easily handled by a pub/sub interface.

It's a clean and simple way of encapsulating complex business logic in your application using simple, stateless objects.

Synopsis

Using Transflow is ridiculously simple as it doesn't make much assumptions about your code. You provide container with operations and they simply need to respond to #call(input) and return output or raise an error if something went wrong.

Defining a simple flow

DB = []

container = {
  validate: -> input { input[:name].nil? ? raise(Transflow::StepError.new("name nil")) : input  },
  persist: -> input { DB << input[:name] }
}

my_business_flow = Transflow(container: container) { steps :validate, :persist }

my_business_flow[{ name: 'Jane' }]

puts DB.inspect
# ["Jane"]

Defining a flow with event publishers

In many cases an individual operation may require additional behavior to be triggered. This can be easily achieved with a pub/sub mechanism. Transflow provides that mechanism through the wonderful wisper gem which is used under the hood.

DB = []

NOTIFICATIONS = [] # just for the sake of the example

class UserPersistListener
  def self.persist_success(user)
    NOTIFICATIONS << "#{user} persisted"
  end

  def self.persist_failure(user, err)
    # do sth about that
  end
end

my_business_flow = Transflow(container: container) do
  step(:validate) { step(:persist, publish: true) }
end

my_business_flow.subscribe(persist: UserPersistListener)

my_business_flow[{ name: 'Jane' }]

puts DB.inspect
# ["Jane"]

puts NOTIFICATIONS.inspect
# ["Jane persisted"]

Passing additional arguments

Another common requirement is to pass aditional arguments that we don't have in the moment of defining our flow. Fortunately Transflow allows you to pass any arguments in the moment you call the transaction. Those arguments will be curried which means you must use either procs as your operation or an object that responds to curry. This limitation will be removed soon.

DB = []

operations = {
  preprocess_input: -> input { { name: input['name'], email: input['email'] } },
  # let's say this one needs additional argument called `email`
  validate_input: -> email, input { input[:email] == email ? input : raise(Transflow::StepError.new('ops')) },
  persist_input: -> input { DB << input[:name] }
}

transflow = Transflow(container: operations) do
  step :preprocess, with: :preprocess_input do
    step :validate, with: :validate_input do
      step :persist, with: :persist_input
    end
  end
end

input = { 'name' => 'Jane', 'email' => 'jane@doe.org' }

# here we say "for `validate` operation curry this additional argument
transflow[input, validate: 'jane@doe.org']

puts DB.inspect
# ["Jane"]

Kleisli Integration

You can use monads from kleisli gem in your steps to achieve a nice control-flow without exceptions:

DB = []

validate = -> input do
  if input[:email]
    Right(input)
  else
    Left("what about the email?")
  end
end

persist = -> input do
  input.fmap do |values|
    DB << values
  end
end

container = { validate: validate, persist: persist }

transflow = Transflow(container: container) do
  monadic true

  steps :validate, :persist
end

transflow[name: 'Jane', email: 'jane@doe.org']
# Right([{:name=>"Jane", :email=>"jane@doe.org"}])

transflow[name: 'Jane']
# Left("what about the email?")

Installation

Add this line to your application's Gemfile:

gem 'transflow'

And then execute:

$ bundle

Or install it yourself as:

$ gem install transflow

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/solnic/transflow.