Add extension for Sequel transactions

[waiting-for-dev]

Overview

We add a Dry::Operation::Extensions::Sequel module that, when included, gives access to a #transaction method. This method wraps the yielded steps in a Sequel transaction, rolling back in case one of them returns a failure.

The extension expects the including class to define a #db method giving access to the Sequel database definition:

class MyOperation < Dry::Operation
  include Dry::Operation::Extensions::Sequel

  attr_reader :db

  def initialize(db:)
    @db = db
  end

  def call(input)
    attrs = step validate(input)
    user = transaction do
      new_user = step persist(attrs)
      step assign_initial_role(new_user)
      new_user
    end
    step notify(user)
    user
  end

  # ...
end

Default options for the #transaction options (which delegates to Sequel transaction method) can be given both at include time with include Dry::Operation::Extensions::Sequel[isolation: :serializable], and at runtime with #transaction(isolation: :serializable).

Screenshots/Screencasts

Details

[waiting-for-dev]

Waiting for #22

[waiting-for-dev]

Setting back to draft as we'll need to apply changes as in #24