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description	Message-Based Autonomous Components
actionText	Get Started →
actionLink	/examples/quickstart.md
features	title details Event Sourcing Business entities projected from persistent streams of events recording the complete history of business activity, with support for caching and snapshotting title details Autonomous Components Message-based components hosted in any number of operating system processes or servers, with actor-based pub-sub consumers, consumer groups, message dispatching, and message handlers title details Pub/Sub Pub/Sub services built on persistent event streams, delivering to consumers in parallel under a hosting runtime
footer	MIT Licensed | Copyright © 2015-present The Eventide Project

---

A Brief Example...

# Account command handler with withdrawal implementation
# Business logic for processing a withdrawal
class Handler
  include Messaging::Handle

  handle Withdraw do |withdraw|
    account_id = withdraw.account_id

    account = store.fetch(account_id)

    unless account.sufficient_funds?(withdraw.amount)
      logger.info('Withdrawal rejected')
      return
    end

    withdrawn = Withdrawn.follow(withdraw)

    time = clock.iso8601
    withdrawn.processed_time = time

    stream_name = stream_name(account_id)

    write.(withdrawn, stream_name)
  end
end

# Withdraw command message
# Send to the account component to effect a withdrawal
class Withdraw
  include Messaging::Message

  attribute :account_id, String
  attribute :amount, Numeric
  attribute :time, String
end

# Withdrawn event message
# Event is written by the handler when a withdrawal is successfully processed
class Withdrawn
  include Messaging::Message

  attribute :account_id, String
  attribute :amount, Numeric
  attribute :time, String
  attribute :processed_time, String
end

# Account entity
# The account component's model object
class Account
  include Schema::DataStructure

  attribute :id, String
  attribute :balance, Numeric, default: -> { 0 }

  def withdraw(amount)
    self.balance -= amount
  end

  def sufficient_funds?(amount)
    balance >= amount
  end
end

# Account entity projection
# Applies account events to an account entity
class Projection
  include EntityProjection

  entity_name :account

  apply Withdrawn do |withdrawn|
    account.id = withdrawn.account_id

    amount = withdrawn.amount

    account.withdraw(amount)
  end
end

# Account entity store
# Projects an account entity and keeps a cache of the result
class Store
  include EntityStore

  entity Account
  projection Projection
end

This code is not a complete implementation and not production-ready. It's intended only to provide a very high-level introductory overview.

Go To Examples →