Eventide

Pub/Sub

Pub/Sub services based on persistent event streams with support for event sourcing, parallelization, and a hosting runtime

Microservices

Message-based services hosted in any number of operating system processes or machines, with actor-based pub-sub consumers, consumer groups, message dispatching, and handlers

Event Sourcing

Business logic entities projected from event streams with caching and snapshotting

# 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 withdrawn = Withdrawn.follow(withdraw)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 withdrawn.processed_time = time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 write.(withdrawn, stream_name)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# Withdrawn event message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class Withdrawn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 apply Withdrawn do |withdrawn|
 account.id = withdrawn.account_id
 amount = withdrawn.amount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

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