Introduction

dry-transaction is a business transaction DSL. It provides a simple way to define a complex business transaction that includes processing over many steps and by many different objects. It makes error handling a primary concern by taking a “Railway Oriented Programming” approach to capturing and returning errors from any step in the transaction.

dry-transaction is based on the following ideas:

  • A business transaction is a series of operations where any can fail and stop the processing.
  • A business transaction may resolve its operations using an external container.
  • A business transaction can describe its steps 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 an operation is #call(input).
  • Each operation provides a meaningful piece of functionality and can be reused.
  • Errors in any operation should be easily caught and handled as part of the normal application flow.

A simple transaction may look like this:

require "dry/transaction"

class CreateUser
  include Dry::Transaction

  step :validate
  step :create

  private

  def validate(input)
    # returns Success(valid_data) or Failure(validation)
  end

  def create(input)
    # returns Success(user)
  end
end

Why?

Allowing a business transaction’s steps to be independent operations directly addressable via a container means that they can be tested in isolation and easily reused throughout your application. The business transaction can then become a series of declarative steps, which ensures that it’s easy to understand at a glance.

The output of each step is a dry-monads Result object (either a Success or Failure). This allows the steps to be chained together and ensures that processing stops in the case of a failure. Returning a Result from the overall transaction also allows for error handling to remain a primary concern without it getting in the way of tidy, straightforward operation logic.

View the full API documentation on RubyDoc.info.

Credits

dry-transaction’s error handling is based on Scott Wlaschin’s Railway Oriented Programming, found via Zohaib Rauf’s Railway Oriented Programming in Elixir blog post. dry-transaction’s behavior as a business transaction library draws heavy inspiration from Piotr Solnica’s Transflow and Gilbert B Garza’s Solid Use Case. Thank you all!