projection_example.rb

module Events
  class Opened
    include Messaging::Message

    attribute :account_id, String
    attribute :customer_id, String
    attribute :time, String
  end

  class Deposited
    include Messaging::Message

    attribute :amount, Numeric
    attribute :time, String
  end

  class Withdrawn
    include Messaging::Message

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


class Account
  include Schema::DataStructure

  attribute :id, String
  attribute :customer_id, String
  attribute :balance, Numeric, default: 0
  attribute :opened_time, Time
  attribute :last_transaction_time, Time

  def deposit(amount)
    self.balance += amount
  end

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

class Projection
  include EntityProjection
  include Events

  entity_name :account

  apply Opened do |opened|
    account.id = opened.account_id
    account.customer_id = opened.customer_id
    account.opened_time = Time.parse(opened.time)
  end

  apply Deposited do |deposited|
    account.deposit(deposited.amount)
    account.last_transaction_time = Time.parse(deposited.time)
  end

  apply Withdrawn do |withdrawn|
    account.withdraw(withdrawn.amount)
    account.last_transaction_time = Time.parse(withdrawn.time)
  end
end


opened = Events::Opened.build({
  customer_id: Identifier::UUID::Random.get,
  time: Clock::UTC.iso8601
})

deposited = Events::Deposited.build({
  amount: 11,
  time: Clock::UTC.iso8601
})

withdrawn = Events::Withdrawn.build({
  amount: 1,
  time: Clock::UTC.iso8601
})


account_id = Identifier::UUID::Random.get

stream_name = Messaging::StreamName.stream_name(account_id, 'account')


batch = [opened, deposited, withdrawn]

Messaging::Postgres::Write.(batch, stream_name)


account = Account.new

EventSource::Postgres::Read.(stream_name) do |event_data|
  Projection.(account, event_data)
end