Postgres messaging for Eventide
The messaging-postgres library contains primitives for writing and reading messages, as well as message handlers and mixins for message schemas and stream name utilities.
account_id = ‘123’
deposit = Deposit.new
deposit.account_id = account_id
deposit.amount = 11
stream_name = StreamName.stream_name(account_id, 'account')
# => 'account-123'
Messaging::Postgres::Write.(deposit, stream_name)
Messaging::Postgres::Read.(stream_name) do |message_data|
AccountComponent::Handlers::Command.(message_data)
endA Handler is the mechanism that receives messages, and takes action based on them.
By including Messaging::Handle, a class becomes a handler. By including Messaging::Postgres::StreamName the handler class receives some useful utilities for composing stream names from constituent parts (category and an entity's ID), and for declaring a the category name that the handler is concerned with (eg: account, fundsTransfer, userProfile, etc).
module AccountComponent
module Handlers
class Commands
include Messaging::Handle
include Messaging::Postgres::StreamName
category :account
handle Deposit do |deposit|
account_id = deposit.account_id
time = clock.iso8601
deposited = Deposited.follow(deposit)
stream_name = stream_name(account_id)
write.(deposited, stream_name, expected_version: version)
end
end
end
endMessages are typically simplistic data structures that carry instructions and responses to and from services.
By including Messaging::Message, a message class can declare attributes that will become part of a message's payload.
module AccountComponent
module Messages
module Commands
class Deposit
include Messaging::Message
attribute :deposit_id, String
attribute :account_id, String
attribute :amount, Numeric
attribute :time, String
end
end
end
end
deposit = AccountComponent::Messages::Commands::Deposit.new
deposit.deposit_id = Identifier::UUID::Random.get
deposit.account_id = account_id
deposit.amount = 11
deposit.time = clock.iso8601The Messaging::Postgres::Read class provides access to streams stored in Postgres. The reader takes a block that receives raw message data, and executes the block for each message data received.
stream_name = 'account-123'
Messaging::Postgres::Read.(stream_name) do |message_data|
puts message_data.type
endThe Messaging::Postgres::Write class writes a message to a stream. The message is converted to raw message data first, then written to the data store.
deposit = AccountComponent::Messages::Commands::Deposit.new
deposit.deposit_id = Identifier::UUID::Random.get
deposit.account_id = account_id
deposit.amount = 11
deposit.time = clock.iso8601
stream_name = 'account-123'
Messaging::Postgres::Write.(deposit, stream_name)For a more in-depth example of the use of this library, see the example projects in the Eventide Examples org on GitHub: https://github.com/eventide-examples
The complete Eventide project documentation can be found at http://eventide-project.org
The messaging-postgres library is released under the MIT License.