Rails Event Store

https://railseventstore.org/docs/
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Rails Event Store is an open-source event store for Ruby and Rails used to publish, consume, store,...
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### Install via RubyGems

Source: https://railseventstore.org/docs/getting-started/install

Install the library using the gem command.

```bash
gem install rails_event_store
```

--------------------------------

### Start databases with devenv up

Source: https://railseventstore.org/docs/contributing/devenv_setup

Starts Postgres 14 and 18, MySQL 8.4, and Redis as background processes. They listen on the same host/port pairs as support/ci/generate, so DATABASE_URL values from CI matrix cells work verbatim. MySQL 9.7 is skipped if no docker-compatible CLI is on PATH.

```bash
devenv up
```

--------------------------------

### Install and run test suites with make

Source: https://railseventstore.org/docs/contributing/devenv_setup

Inside the devenv shell, install gem dependencies once, then use the regular make targets. The test-ruby_event_store target needs no database, while test-ruby_event_store-active_record runs against Postgres 18 by default.

```bash
make install-ruby_event_store                  # bundle install for that gem

make test-ruby_event_store                     # no database needed

make install-ruby_event_store-active_record    # bundle install for that gem

make test-ruby_event_store-active_record       # against Postgres 18 by default
```

--------------------------------

### Install in existing Rails application

Source: https://railseventstore.org/docs/getting-started/install

Run the template in an existing Rails application root directory.

```bash
bin/rails app:template LOCATION=https://railseventstore.org/new
```

--------------------------------

### Install SQL adapter gems

Source: https://railseventstore.org/docs/advanced-topics/without-rails

Choose and install one of the supported SQL adapters: SQLite3, PostgreSQL, or MySQL.

```ruby
# Choose one of SQL adapters  
gem "sqlite3"  

gem "pg"  

gem "mysql2"  
```

--------------------------------

### Install ruby_event_store-cli

Source: https://railseventstore.org/docs/core-concepts/cli

Add the gem to your application's Gemfile to enable the res command.

```ruby
gem "ruby_event_store-cli"
```

--------------------------------

### Implementing a Complete Extension Class

Source: https://railseventstore.org/docs/core-concepts/browser

A full example of an extension class implementing views_root, assets_root, register_routes, stream_links, and nav_links.

```ruby
class DeploymentsExtension  

  def views_root  

    File.expand_path("browser_views", __dir__)  

  end  

  

  def assets_root  

    File.expand_path("browser_assets", __dir__)  

  end  

  

  def register_routes(router, context)  

    router.add_route("GET", "/deployments/:name") do |params, urls|  

      name = params.fetch("name")  

      events = context.event_store.read.stream("Deployment$#{name}").to_a  

      next context.not_found(urls, message: "No deployment named #{name}") if events.empty?  

  

      context.render("deployments/show", urls: urls, title: "Deployment #{name}", name: name, events: events)  

    end  

  end  

  

  def stream_links(stream_name, urls)  

    prefix, name = stream_name.split("$")  

    return [] unless prefix == "Deployment"  

    [{ label: "Deployment view", url: urls.app_url_for("deployments", name) }]  

  end  

  

  def nav_links(urls)  

    [{ label: "Deployments", url: urls.app_url_for("deployments", "production") }]  

  end  

end  
```

--------------------------------

### Install custom repository with Bundler

Source: https://railseventstore.org/docs/advanced-topics/custom-repository

Adds the rails_event_store gem with the 'rails_event_store/all' require and a custom repository gem to the Gemfile. Run bundle install after adding these lines.

```ruby
gem "rails_event_store", require: "rails_event_store/all"  

gem "your_custom_repository"  

```

--------------------------------

### Use custom OrderRepository

Source: https://railseventstore.org/docs/core-concepts/event-sourcing

Example of submitting an order using the custom OrderRepository.

```ruby
repository = OrderRepository.new  
repository.with_order(123) do |order|  

  order.submit  

end  
```

--------------------------------

### Example payload for load.repository.aggregate_root

Source: https://railseventstore.org/docs/advanced-topics/instrumentation

Shown under the load.repository.aggregate_root heading. The payload contains :aggregate and :stream keys.

```ruby
{

  aggregate: #<Order:0x00000001141f97c0>,

  stream: "Order$42"

}
```

--------------------------------

### Example payload for apply.aggregate_root

Source: https://railseventstore.org/docs/advanced-topics/instrumentation

Shown under the apply.aggregate_root heading. The payload contains :aggregate and :event keys.

```ruby
{

  aggregate: #<Order:0x00000001141f97c0>,

  event: #<Orders::Events::OrderCreated:0x000000011428a950>

}
```

--------------------------------

### Example payload for store.repository.aggregate_root

Source: https://railseventstore.org/docs/advanced-topics/instrumentation

Shown under the store.repository.aggregate_root heading. The payload contains :aggregate, :stream, :version, and :stored_events keys.

```ruby
{

  aggregate: #<Order:0x00000001141f97c0>,

  stream: "Order$42",

  version: -1,

  stored_events: [

    #<Orders::Events::OrderCreated:0x000000011428a950>,

    #<Orders::Events::OrderExpired:0x000000011428a2c0>

  ]

}
```

--------------------------------

### have_published from a starting point

Source: https://railseventstore.org/docs/core-concepts/rspec

Specifies the reading starting point for the matcher using an event ID.

```ruby
expect(event_store).to have_published(an_event(OrderExpired)).from(order_placed.event_id)  
```

--------------------------------

### Install minitest-ruby_event_store

Source: https://railseventstore.org/docs/minitest.html

Add the gem to your Gemfile and require it in your test helper to mix assertions into Minitest::Assertions.

```ruby
group :test do  

  gem "minitest-ruby_event_store"  

end  
```

```ruby
require "minitest/ruby_event_store"  
```

--------------------------------

### Install Rails Event Store and Protobuf gems

Source: https://railseventstore.org/docs/advanced-topics/protobuf.html

Add these dependencies to your Gemfile to enable Protobuf support in Rails Event Store.

```ruby
gem "google-protobuf"

gem "protobuf_nested_struct"

gem "rails_event_store"

gem "ruby_event_store-protobuf"
```

--------------------------------

### Publish event with custom mapper

Source: https://railseventstore.org/docs/advanced-topics/mappers

Example of publishing an event using the configured event store with the custom mapper.

```ruby
class OrderPlaced < RubyEventStore::Event  

end  

event_store = Rails.configuration.event_store  

event_store.publish(OrderPlaced.new(data: {  

  'order_id' => 1,  

  'order_amount' => BigDecimal('120.55'),  

}), stream_name: 'Order$1')  

```

--------------------------------

### Sparse matrix configuration

Source: https://railseventstore.org/docs/contributing/ci_workflows

Example of using the sparse matrix DSL to limit the number of test rows while ensuring each value is exercised at least once.

```ruby
sparse(ruby_version("4.0", "3.4", "3.3"), bundle_gemfile("G", "R1", "R2"))  

# => 5 rows, not 9:  

#   {ruby 4.0, G} {ruby 3.4, G} {ruby 3.3, G}   # ruby varies at the baseline gemfile  

#   {ruby 4.0, R1} {ruby 4.0, R2}               # gemfile varies at the baseline ruby
```

--------------------------------

### Implement a listener with call method

Source: https://railseventstore.org/docs/core-concepts/pubsub

Implement a listener that responds to call and handles events by class. The example raises an error for unsupported events.

```ruby
class OrderNotifier  
  def call(event)  
    order_id = order.data.fetch(:order_id)  
    case event  
    when OrderCancelled  
      # notify someone...  
    else  
      raise "not supported event #{event.inspect}"  
    end  
  end  
end  

```

--------------------------------

### Setup Upcast Mapper

Source: https://railseventstore.org/docs/advanced-topics/migrating-existing-events

Configure the RubyEventStore::Mappers::Transformation::Upcast in your mapper pipeline by providing a hash of event types and transformation lambdas.

```ruby
upcast_map = {  

  "OrderPlaced" => lambda do |record|  

    RubyEventStore::Record.new(  

      event_id:   record.event_id,  

      metadata:   record.metadata,  

      timestamp:  record.timestamp,  

      valid_at:   record.valid_at,  

      event_type: record.event_type,  

      data:       record.data.merge(currency: "USD"),  

    )  

  end  

}  

  

class MyMapper < RubyEventStore::Mappers::PipelineMapper  

  def initialize(upcast_map)  

    super(RubyEventStore::Mappers::Pipeline.new(  

      RubyEventStore::Mappers::Transformation::Upcast.new(upcast_map),  

      RubyEventStore::Mappers::Transformation::SymbolizeMetadataKeys.new,  

    ))  

  end  

end  

  

Rails.application.configure do  

  config.to_prepare do  

    Rails.configuration.event_store = RailsEventStore::Client.new(  

      mapper: MyMapper.new(upcast_map)  

    )  

  end  

end
```

--------------------------------

### Defining an Extension Template

Source: https://railseventstore.org/docs/core-concepts/browser

An example of an ERB template file located in the extension's views_root directory.

```erb
<h1>Deployment <%= h(name) %></h1>  

<ul>  

  <% events.each do |event| -%>  

    <li>  

      <a href="<%= urls.event_url(event.event_id) %>"><%= h(event.event_type) %></a>  

      <%= render("_timestamp", title: "At", time: event.metadata[:timestamp], top: false) %>  

    </li>  

  <% end -%>  

</ul>  
```

--------------------------------

### Add ruby_event_store-mcp to Gemfile

Source: https://railseventstore.org/docs/core-concepts/mcp

Add this line to your application's Gemfile to install the res-mcp binary. The binary speaks MCP over stdio and loads config/environment.rb from your app's root.

```ruby
gem "ruby_event_store-mcp"
```

--------------------------------

### JSON symbol-to-string conversion example

Source: https://railseventstore.org/docs/advanced-topics/event-serialization-formats

Shows that JSON.load converts symbol keys to strings, which is a caveat when using JSON serialization.

```ruby
JSON.load(JSON.dump({ foo: :bar }))  
# => {"foo" => "bar"}  

```

--------------------------------

### Configure ROM container and repository

Source: https://railseventstore.org/docs/advanced-topics/without-rails

Set up the ROM environment and initialize the Ruby Event Store client with the ROM repository.

```ruby
require "ruby_event_store/rom/sql"  

  

# Use the `setup` helper to configure repositories and mappers.  

# Then store an Env instance to get access to the ROM container.  

RubyEventStore::ROM.env = RubyEventStore::ROM.setup(:sql, ENV["DATABASE_URL"])  

  

# Use the repository the same as with ActiveRecord  

client = RubyEventStore::Client.new(repository: RubyEventStore::ROM::EventRepository.new)  
```

--------------------------------

### Correlate events and commands with RubyEventStore::CorrelatedCommands

Source: https://railseventstore.org/docs/core-concepts/correlation-causation

Wires the event store and command bus together using RubyEventStore::CorrelatedCommands in a Rails to_prepare block. This makes events automatically correlated to the commands that triggered them, provided commands respond to message_id. The example shows the setup with placeholders for registering handlers and commands.

```ruby
config.to_prepare do  
  Rails.configuration.event_store = event_store = RailsEventStore::Client.new  

  

  # register handlers  

  

  command_bus = Arkency::CommandBus.new  

  

  # register commands...  

  

  # wire event_store and command_bus together  
  Rails.configuration.command_bus = RubyEventStore::CorrelatedCommands.new(event_store, command_bus)  
end  
```

--------------------------------

### Run the browser demo

Source: https://railseventstore.org/docs/contributing/devenv_setup

Serves the standalone browser demo, seeded with sample events, at http://localhost:9393.

```bash
make -C ruby_event_store-browser dev
```

--------------------------------

### Configure AggregateRoot::Repository

Source: https://railseventstore.org/docs/core-concepts/event-sourcing

Initialize the repository by passing the event store client explicitly, as there is no global default.

```ruby
event_store = Rails.configuration.event_store  

repository  = AggregateRoot::Repository.new(event_store)  
```

--------------------------------

### Handle RubyEventStore::InvalidPageStart

Source: https://railseventstore.org/docs/core-concepts/client-errors

Occurs when reading a stream with an invalid start parameter.

```ruby
expect do  

  client.read.stream('Order$1').from(nil).to_a  

end.to raise_error(InvalidPageStart)  
```

--------------------------------

### Instantiate client in config/application

Source: https://railseventstore.org/docs/getting-started/install

Configure the event store client within the main application configuration.

```ruby
# config/application.rb
module YourAppName
  class Application < Rails::Application
    config.to_prepare do
      Rails.configuration.event_store = RailsEventStore::Client.new
      # add subscribers here
    end
  end
end
```

--------------------------------

### Enter the devenv shell

Source: https://railseventstore.org/docs/contributing/devenv_setup

Run this from the repository root to enter a shell with the correct Ruby, bundler, and native libraries for the pg, mysql2, and sqlite3 gems. The first run builds or downloads the toolchain via Cachix.

```bash
devenv shell
```

--------------------------------

### Run migration with custom paths

Source: https://railseventstore.org/docs/advanced-topics/without-rails

Execute database migrations while specifying custom directory paths and database connection details.

```bash
MIGRATION_DIR=migration_path DATABASE_DIR=db_dir DATABASE_URL=postgres://localhost/somedb_development bundle exec rake db:migrate
```

--------------------------------

### Instantiate client in config/environments

Source: https://railseventstore.org/docs/getting-started/install

Configure the event store client within the Rails environment configuration.

```ruby
# config/environments/*.rb

Rails.application.configure do
  config.to_prepare do
    Rails.configuration.event_store = RailsEventStore::Client.new
    # add subscribers here
  end
end
```

--------------------------------

### Defining current_user in ApplicationController

Source: https://railseventstore.org/docs/core-concepts/request-metadata

A basic setup for an ApplicationController method that retrieves the currently logged-in user.

```ruby
class ApplicationController < ActionController::Base  

  def current_user  

    # ...  

  end  

end  
```

--------------------------------

### Generate outbox migration

Source: https://railseventstore.org/docs/advanced-topics/outbox

Run this command to create the necessary database tables for the outbox.

```bash
bin/rails generate ruby_event_store:outbox:migration
```

--------------------------------

### Instantiate client in initializer

Source: https://railseventstore.org/docs/getting-started/install

Configure the event store client within a dedicated initializer file.

```ruby
# config/initializers/rails_event_store.rb
Rails.configuration.to_prepare do
  Rails.configuration.event_store = RailsEventStore::Client.new
  # add subscribers here
end
```

--------------------------------

### Read all events backward with no limit

Source: https://railseventstore.org/docs/core-concepts/read

Loads all stored events in descending order, starting from the last event, with no limit applied.

```ruby
client.read.backward.to_a  

```

--------------------------------

### Read all events forward with no limit

Source: https://railseventstore.org/docs/core-concepts/read

Loads all stored events in ascending order, starting from the first event, with no limit applied.

```ruby
client.read.to_a  

```

--------------------------------

### Read stream forward from first event

Source: https://railseventstore.org/docs/core-concepts/read

Reads up to 40 events from a stream in ascending order, starting from the first event.

```ruby
stream_name = "order_1"  

count = 40  

client.read.stream(stream_name).limit(count).to_a  

```

--------------------------------

### Create new Rails application with template and database option

Source: https://railseventstore.org/docs/getting-started/install

Specify additional rails new options like database type when using the template.

```bash
rails new -m https://railseventstore.org/new APP_NAME --database=postgresql
```

--------------------------------

### Repository initialize with serializer

Source: https://railseventstore.org/docs/custom_components_2_0.html

The Repository's initialize method now takes a serializer argument, which is stored in an instance variable for later use.

```ruby
def initialize(serializer)  

  @serializer = serializer  

end  

```

--------------------------------

### Perform database migration

Source: https://railseventstore.org/docs/advanced-topics/without-rails

Execute the database migration using the DATABASE_URL environment variable.

```bash
DATABASE_URL=postgres://localhost/somedb_development bundle exec rake db:migrate
```

--------------------------------

### Read stream forward from a given event

Source: https://railseventstore.org/docs/core-concepts/read

Reads up to 40 events from a stream in ascending order, starting from a specific event identified by its event_id.

```ruby
# last_read_event is any domain event read or published by rails_event_store  

stream_name = "order_1"  

start = last_read_event.event_id  

count = 40  

client.read.stream(stream_name).from(start).limit(count).to_a  

```

--------------------------------

### Generate and run migrations for Sqlite

Source: https://railseventstore.org/docs/getting-started/install

Generate and run the migration for Sqlite databases.

```bash
bin/rails generate ruby_event_store:active_record:migration

bin/rails db:migrate
```

--------------------------------

### Instantiate JSON client

Source: https://railseventstore.org/docs/getting-started/install

Use the JSONClient for optimized performance with PostgreSQL jsonb data types.

```ruby
Rails.configuration.event_store = RailsEventStore::JSONClient.new
```

--------------------------------

### Run database migration tasks

Source: https://railseventstore.org/docs/advanced-topics/without-rails

Use Rake tasks to copy migration files to your project and execute them to set up the database tables.

```bash
# Copies the migrations to your project (in db/migrate)  
bundle exec rake db:migrations:copy DATABASE_URL=postgres://localhost/database  
# <= migration file created db/migrate/20180417201709_create_ruby_event_store_tables.rb  

# Runs the migrations and creates the tables  
bundle exec rake db:migrate DATABASE_URL=postgres://localhost/database  
# <= db:migrate executed  
```

--------------------------------

### Read events forward from a given event with limit

Source: https://railseventstore.org/docs/core-concepts/read

Reads a batch of domain events starting from any read or published event, limited to 100 events.

```ruby
client.read.from(last_read_event.event_id).limit(100).to_a  

```

--------------------------------

### Configure custom repository in Rails application

Source: https://railseventstore.org/docs/advanced-topics/custom-repository

Sets up RailsEventStore::Client with a custom repository instance in a Rails to_prepare block. Replace YourCustomRepository with your actual repository class.

```ruby
Rails.application.configure do  
  config.to_prepare do  
    Rails.configuration.event_store = RailsEventStore::Client.new(repository: YourCustomRepository.new)  
  end  
end  

```

--------------------------------

### Read stream backward from a given event

Source: https://railseventstore.org/docs/core-concepts/read

Reads up to 40 events from a stream in descending order, starting from a specific event. Append .backward before .each as shown.

```ruby
stream_name = "order_1"  

start = last_read_event.event_id  

count = 40  

client.read.backward.stream(stream_name).from(start).limit(count).to_a  

```

--------------------------------

### Create new Rails application with template

Source: https://railseventstore.org/docs/getting-started/install

Use the Rails template to automatically configure RailsEventStore in a new application.

```bash
rails new -m https://railseventstore.org/new APP_NAME
```

--------------------------------

### Narrow projection scope with from on a single stream

Source: https://railseventstore.org/docs/core-concepts/projections

Runs the same account_balance projection but starts from a specific event using client.read.stream(stream_name).from(custom_event.event_id), returning {total: -5}.

```ruby
account_balance.call(client.read.stream(stream_name).from(custom_event.event_id)) # => {total: -5}  
```

--------------------------------

### Copy migration file

Source: https://railseventstore.org/docs/advanced-topics/without-rails

Run the rake task to generate the necessary database migration file.

```bash
DATA_TYPE=jsonb DATABASE_URL=postgres://localhost/somedb_development bundle exec rake db:migrations:copy
```

--------------------------------

### Configure Protobuf mapper

Source: https://railseventstore.org/docs/advanced-topics/protobuf.html

Initialize the Rails Event Store client with the Protobuf mapper within your Rails configuration.

```ruby
require "ruby_event_store/protobuf"

  

Rails.application.configure do  

  config.to_prepare do  

    Rails.configuration.event_store = RailsEventStore::Client.new(mapper: RubyEventStore::Mappers::Protobuf.new)  

  end  

end
```

--------------------------------

### Handle exceptions in synchronous handlers

Source: https://railseventstore.org/docs/core-concepts/subscribe

Synchronous handlers that raise exceptions can cause transaction rollbacks. This example shows how to wrap the handler logic in a rescue block to prevent bubbling.

```ruby
class SyncHandler  

  def call(event)  

    # ...  

  rescue => e  

    ExceptionTracker.notify(e)  

  end  

end  
```

--------------------------------

### Subscribe an object handler with within and subscribe

Source: https://railseventstore.org/docs/core-concepts/pubsub

Subscribe an object responding to call as an event handler. The example shows subscribing a listener to OrderCancelled events within a block that calls cancel_order.

```ruby
cancel_order = CancelOrder.new  
event_store = Rails.configuration.event_store  
listener = OrderNotifier.new  
  
event_store.within { cancel_order.call(order_id, user_id) }.subscribe(listener, to: [OrderCancelled]).call  

```

--------------------------------

### Copy migration file with custom path

Source: https://railseventstore.org/docs/advanced-topics/without-rails

Generate the migration file using a custom path configuration.

```bash
DATA_TYPE=jsonb MIGRATION_PATH=database/migrations bundle exec rake db:migrations:copy
```

--------------------------------

### Set environment variables manually for a CI cell

Source: https://railseventstore.org/docs/contributing/devenv_setup

Alternative to res-cell: set DATABASE_URL and DATA_TYPE by hand before running the make target. The example uses the Postgres 14 URL and jsonb data type.

```bash
DATABASE_URL=postgres://postgres:secret@localhost:10014/rails_event_store \
  DATA_TYPE=jsonb make test-ruby_event_store-active_record
```

--------------------------------

### Initialize Client with Custom Scheduler

Source: https://railseventstore.org/docs/core-concepts/subscribe

Configure the RailsEventStore::Client to use an asynchronous dispatcher with a custom scheduler.

```ruby
event_store =  

  RailsEventStore::Client.new(  

    message_broker: RubyEventStore::Broker.new(  

      dispatcher: RailsEventStore::AfterCommitDispatcher.new(scheduler: CustomScheduler.new),  

    ),  

  )
```

--------------------------------

### Mounting Browser in Rack config.ru

Source: https://railseventstore.org/docs/core-concepts/browser

Configure the browser in your Rack application by providing an event store locator to the app.

```ruby
# e.g. config.ru  
  
require "ruby_event_store/browser/app"  
  
# Example RES client you might configure  
event_store = RubyEventStore::Client.new(repository: RubyEventStore::InMemoryRepository.new)  
  
run RubyEventStore::Browser::App.for(event_store_locator: -> { event_store })  
```

--------------------------------

### Correlate an event with a command using correlate_with

Source: https://railseventstore.org/docs/core-concepts/correlation-causation

Correlates an event with a command by calling correlate_with on the event. The command must respond to correlation_id (can be nil) and message_id. The example creates an ApproveOrder command and an OrderApproved event, then correlates them.

```ruby
class ApproveOrder < Struct.new(:order_id, :message_id, :correlation_id)  
end  

  

command = ApproveOrder.new("KTXBN123", SecureRandom.uuid, nil)  

event = OrderApproved.new(data: { foo: "bar" })  

event.correlate_with(command)  
```

--------------------------------

### Implement a Custom Scheduler

Source: https://railseventstore.org/docs/core-concepts/subscribe

Create a custom scheduler by implementing call and verify methods to define how subscribers are scheduled.

```ruby
class CustomScheduler  

  # method doing actual schedule; record is a RubyEventStore::Record  

  def call(klass, record)  

    klass.perform_async(record.serialize(RubyEventStore::Serializers::YAML).to_h)  

  end  

  

  # method which is checking whether given subscriber is correct for this scheduler  

  def verify(subscriber)  

    Class === subscriber && subscriber.respond_to?(:perform_async)  

  end  

end
```

--------------------------------

### Custom event adapter to preserve symbol keys

Source: https://railseventstore.org/docs/advanced-topics/event-serialization-formats

Defines a custom event class that wraps data in ActiveSupport::HashWithIndifferentAccess to shield from symbol-to-string conversion. Includes usage example showing both symbol and string access work.

```ruby
class MyEvent < RubyEventStore::Event  
  def data  
    ActiveSupport::HashWithIndifferentAccess.new(super)  
  end  
end  
  
OrderPlaced = Class.new(MyEvent)  

```

```ruby
event_store.publish(OrderPlaced.new(event_id: 'e34fc19a-a92f-4c21-8932-a10f6fb2602b', data: { foo: :bar }))  
event = event_store.read.event('e34fc19a-a92f-4c21-8932-a10f6fb2602b')  
  
event.data[:foo]  
# => "bar"  
  
event.data['foo']  
# => "bar"  

```

--------------------------------

### Correlate commands with events using CorrelableCommand module

Source: https://railseventstore.org/docs/core-concepts/correlation-causation

Defines a CorrelableCommand module that adds correlation_id and causation_id attributes and a correlate_with method. Commands including this module can be correlated to events that triggered them inside sync handlers. The AddProductCommand example includes the module and initializes with a generated message_id.

```ruby
module CorrelableCommand  
  attr_accessor :correlation_id, :causation_id  

  

  def correlate_with(other_message)  
    self.correlation_id = other_message.correlation_id || other_message.message_id  
    self.causation_id = other_message.message_id  
  end  
end  

  

class AddProductCommand < Struct.new(:message_id, :product_id)  
  include CorrelableCommand  

  

  def initialize(product_id:, message_id: SecureRandom.uuid)  
    super(message_id, product_id)  
  end  
end  
```

--------------------------------

### Generate bounded context folders

Source: https://railseventstore.org/docs/getting-started/introduction

Use the bounded_context generator to initialize the folder structure for a new domain model.

```bash
rails generate rails_event_store:bounded_context YOUR-BOUNDED-CONTEXT-NAME
```

--------------------------------

### Use an alternative Ruby version with res-ruby-3.4

Source: https://railseventstore.org/docs/contributing/devenv_setup

Prefix a command with res-ruby-3.4 to reproduce a 3.4 cell. Each version keeps its own gem home so native extensions never clash.

```bash
res-ruby-3.4 make test-ruby_event_store-active_record
```

--------------------------------

### Configure global event subscribers in config/application.rb

Source: https://railseventstore.org/docs/core-concepts/pubsub

Configure global event subscribers in config/application.rb. The event store is created and a listener is subscribed to OrderCancelled events during the to_prepare hook.

```ruby
# config/application.rb  
module YourAppName  
  class Application < Rails::Application  
    config.to_prepare do  
      Rails.configuration.event_store = event_store = RailsEventStore::Client.new  
      event_store.subscribe(OrderNotifier.new, to: [OrderCancelled])  
    end  
  end  
end  

```

--------------------------------

### Registering a Browser Extension

Source: https://railseventstore.org/docs/core-concepts/browser

Register an extension by passing an instance to the extensions array in the RubyEventStore::Browser::App configuration.

```ruby
run RubyEventStore::Browser::App.for(  

  event_store_locator: -> { event_store },  

  extensions: [DeploymentsExtension.new],  

)  
```

--------------------------------

### Implement InMemoryEncryptionKeyRepository interface

Source: https://railseventstore.org/docs/advanced-topics/gdpr

Reference implementation of a key repository with methods key_of, create, and forget. Uses aes-256-cbc cipher and generates random keys. This interface must be implemented for production use.

```ruby
class InMemoryEncryptionKeyRepository  

  DEFAULT_CIPHER = "aes-256-cbc".freeze  

  

  def initialize  

    @keys = {}  

  end  

  

  def key_of(identifier, cipher: DEFAULT_CIPHER)  

    @keys[[identifier, cipher]]  

  end  

  

  def create(identifier, cipher: DEFAULT_CIPHER)  

    @keys[[identifier, cipher]] = RubyEventStore::Mappers::EncryptionKey.new(cipher: cipher, key: random_key(cipher))  

  end  

  

  def forget(identifier)  

    @keys = @keys.reject { |(id, _)| id.eql?(identifier) }  

  end  

  

  private  

  

  def random_key(cipher)  

    crypto = OpenSSL::Cipher.new(cipher)  

    crypto.encrypt  

    crypto.random_key  

  end  

end  
```

--------------------------------

### Configuring command bus with to_prepare

Source: https://railseventstore.org/docs/advanced-topics/command-bus

Uses the Rails to_prepare callback to re-register commands, ensuring the command bus works correctly after code reloads.

```ruby
config.to_prepare do  

  config.command_bus = Arkency::CommandBus.new  

  register = command_bus.method(:register)  

  

  { FooCommand => FooService.new(event_store: event_store).method(:foo), BarCommand => BarService.new }.map(&register)  

end  
```

--------------------------------

### Configure event store with Outbox SidekiqScheduler

Source: https://railseventstore.org/docs/advanced-topics/outbox

Update your event store client configuration to use the ImmediateDispatcher with the SidekiqScheduler.

```ruby
RailsEventStore::Client.new(
  message_broker:
    RubyEventStore::Broker.new(
      dispatcher:
        RubyEventStore::ComposedDispatcher.new(
          RubyEventStore::ImmediateDispatcher.new(scheduler: RubyEventStore::Outbox::SidekiqScheduler.new),
          RubyEventStore::SyncScheduler.new,
        ),
    ),
)
```

--------------------------------

### Building URLs with app_url_for

Source: https://railseventstore.org/docs/core-concepts/browser

Use the urls.app_url_for helper to generate paths relative to the browser mount point, avoiding hardcoded paths.

```ruby
urls.app_url_for("deployments", name)  

urls.app_url_for("deployments", query: [["env[]", "production"]])  
```

--------------------------------

### Create a custom OrderRepository

Source: https://railseventstore.org/docs/core-concepts/event-sourcing

Encapsulate repository logic in a custom class to simplify aggregate interactions.

```ruby
class OrderRepository  

  def initialize(event_store = Rails.configuration.event_store)  

    @repository = AggregateRoot::Repository.new(event_store)  

  end  

  

  def with_order(order_id, &block)  

    stream_name = "Order$#{order_id}"  

    repository.with_aggregate(Order.new, stream_name, &block)  

  end  

  

  private  

  attr_reader :repository  

end  
```

--------------------------------

### Implement apply_strategy with Hash lookup

Source: https://railseventstore.org/docs/core-concepts/event-sourcing

Shows an alternative implementation of apply_strategy using a Hash to map event types to methods.

```ruby
def apply_strategy  

    ->(aggregate, event) do  

      {  

        'OrderExpired' => method(:order_has_expired),  

        'OrderSubmitted' => method(:order_has_been_submitted),  

      }.fetch(event.event_type, ->(event) { raise }).call(event)  

    end  

  end  

  

  def order_has_been_submitted(event)  

    @state = :submitted  

  end  

  

  def order_has_expired(event)  

    @state = :expired  

  end  
```

--------------------------------

### Run the res_outbox process

Source: https://railseventstore.org/docs/advanced-topics/outbox

Execute the outbox process to drain the database table to Redis.

```bash
res_outbox \
  --database-url="mysql2://root@0.0.0.0:3306/my_database" \
  --redis-url="redis://localhost:6379/0" \
  --log-level=info \
  --split-keys=sidekiq_queue1,sidekiq_queue2
```

--------------------------------

### Manual stream matching

Source: https://railseventstore.org/docs/core-concepts/rspec

A verbose approach using 'match' instead of 'have_published' for custom requirements.

```ruby
expect(event_store.read.stream("OrderAuditLog$42").limit(2).to_a).to match(  

  [an_event(OrderPlaced), an_event(OrderExpired)],  

)  
```

--------------------------------

### Run res_outbox with metrics

Source: https://railseventstore.org/docs/advanced-topics/outbox

Execute the outbox process with an InfluxDB metrics URL configured.

```bash
res_outbox --database-url="mysql2://root@0.0.0.0:3306/my_database" \
  --redis-url="redis://localhost:6379/0" \
  --log-level=info \
  --split-keys=sidekiq_queue1,sidekiq_queue2 \
  --metrics-url=http://user:password@localhost:8086/dbname
```

--------------------------------

### Add SQL adapter gems to Gemfile

Source: https://railseventstore.org/docs/advanced-topics/without-rails

Include the required SQL adapter gem for your database choice.

```ruby
# Gemfile  

# ...  

gem "sqlite3"  

gem "pg"  

gem "mysql2"
```

--------------------------------

### CLI event show command

Source: https://railseventstore.org/docs/core-concepts/cli

Displays full details for a single event, including data and metadata, using the event ID.

```bash
$ bundle exec res event show 59588873-00fa-423f-89d1-03d7c3b0ab35  

Event ID:   59588873-00fa-423f-89d1-03d7c3b0ab35  

Type:       OrderPlaced  

Timestamp:  2026-03-24T17:45:03.891Z  

Valid at:   2026-03-24T17:45:03.891Z  

Data:       {  

  "order_id": "f47ac10b-58cc-4372-a567-0e02b2c3d479",  

  "customer_id": "c-1024",  

  "total": "149.00"  

}  

Metadata:   {  

  "correlation_id": "452fd6f0-e3a2-4716-bc8a-43bbcf2cae61",  

  "causation_id": "452fd6f0-e3a2-4716-bc8a-43bbcf2cae61"  

}  
```

--------------------------------

### Configure RES client in config/application.rb

Source: https://railseventstore.org/docs/core-concepts/pubsub

Configure the Rails Event Store client in the application's config/application.rb file. The client is assigned to Rails.configuration.event_store during the to_prepare hook.

```ruby
# config/application.rb  
module YourAppName  
  class Application < Rails::Application  
    config.to_prepare { Rails.configuration.event_store = RailsEventStore::Client.new }  
  end  
end  

```

--------------------------------

### Using the convenience alias

Source: https://railseventstore.org/docs/advanced-topics/command-bus

Requires the alias file to enable the use of the top-level CommandBus constant.

```ruby
require "arkency/command_bus/alias"  
```

--------------------------------

### Read first 100 events forward

Source: https://railseventstore.org/docs/core-concepts/read

Loads the first 100 domain events stored in the event store in ascending order.

```ruby
client.read.limit(100).to_a  

```

--------------------------------

### CLI search command

Source: https://railseventstore.org/docs/core-concepts/cli

Searches across the entire event store using filters like --type, --after, --before, and --limit, with an optional --stream scope.

```bash
$ bundle exec res search --type OrderPlaced --after 2026-03-01T00:00:00Z  

EVENT ID                              TYPE                                      TIMESTAMP  

------------------------------------------------------------------------------------------  

59588873-00fa-423f-89d1-03d7c3b0ab35  OrderPlaced                               2026-03-24T17:45:03.891Z  

8b1f2c3d-1a2b-4c3d-9e8f-7a6b5c4d3e2f  OrderPlaced                               2026-03-22T09:13:55.620Z  

  

2 event(s)  
```

--------------------------------

### Generate and run migrations for PostgreSQL

Source: https://railseventstore.org/docs/getting-started/install

Generate and run the migration for PostgreSQL using the jsonb data type.

```bash
bin/rails generate ruby_event_store:active_record:migration --data-type=jsonb

bin/rails db:migrate
```
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