https://github.com/elixir-toniq/maestro

an event store + cqrs
https://github.com/elixir-toniq/maestro

Last synced: about 1 month ago
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an event store + cqrs

• Host: GitHub
• URL: https://github.com/elixir-toniq/maestro
• Owner: elixir-toniq
• License: apache-2.0
• Created: 2017-10-12T15:12:38.000Z (about 7 years ago)
• Default Branch: master
• Last Pushed: 2021-07-22T21:18:39.000Z (over 3 years ago)
• Last Synced: 2024-05-01T12:25:26.294Z (8 months ago)
• Language: Elixir
• Homepage:
• Size: 169 KB
• Stars: 116
• Watchers: 11
• Forks: 3
• Open Issues: 6
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

• awesome-elixir-cqrs - Maestro - An Elixir event store + CQRS library. (Libraries)

README

        
# Maestro

Maestro is an event sourcing _library_. It is inspired by CQRS and re-uses

terminology where appropriate. The divergence from being a CQRS framework is

intentional as Maestro focuses on processing commands in a consistent manner and

replaying events in a consistent order.

Currently, the only storage adapter suited to a multi-node environment is the

`Maestro.Store.Postgres` adapter. The `Maestro.Store.InMemory` adapter exists

for testing purposes only.

## Status

[![Hex](http://img.shields.io/hexpm/v/maestro.svg?style=flat)](https://hex.pm/packages/maestro)

[![Build Status](https://travis-ci.org/toniqsystems/maestro.svg?branch=master)](https://travis-ci.org/toniqsystems/maestro)

[![Coverage](https://coveralls.io/repos/github/toniqsystems/maestro/badge.svg)](https://coveralls.io/github/toniqsystems/maestro)

Documentation is available [here](https://hexdocs.pm/maestro/).

## Installation

```elixir

def deps do

  [{:maestro, "~> 0.2"}]

end

```

## Database Configuration

Maestro is intended to be used alongside an existing database/ecto repo.

```elixir

config :maestro,

  storage_adapter: Maestro.Store.Postgres,

  repo: MyApp.Repo

```

To generate the migrations for the snapshot and event logs, do:

```bash

mix maestro.create.event_store_migration

```

## Example

There are three behaviours that make the command/event lifecycle flow:

`Maestro.Aggregate.CommandHandler`, `Maestro.Aggregate.EventHandler`, and

`Maestro.Aggregate.ProjectionHandler`. Modules implementing the command and

event handler behaviours are looked up via a configurable `:command_prefix` and

`:event_prefix` respectively. Projections are reserved for maintaining other

models/representations within the event's transaction.

```elixir

defmodule MyApp.Aggregate do

  use Maestro.Aggregate.Root,

    command_prefix: MyApp.Aggregate.Commands,

    event_prefix: MyApp.Aggregate.Events

  def initial_state, do: %{"value" => 0}

  def prepare_snapshot(state), do: state

  def use_snapshot(_curr, %Maestro.Types.Snapshot{body: state}), do: state

end

defmodule MyApp.Aggregate.Commands.IncrementCounter do

  @behaviour Maestro.Aggregate.CommandHandler

  alias Maestro.Types.Event

  def eval(aggregate, _command) do

    [

      %Event{

        aggregate_id: aggregate.id,

        type: "counter_incremented",

        body: %{}

      }

    ]

  end

end

defmodule MyApp.Aggregate.Events.CounterIncremented do

  @behaviour Maestro.Aggregate.EventHandler

  def apply(state, _event), do: Map.update!(state, "value", &(&1 + 1))

end

```

```elixir

iex(1)> {:ok, id} = MyApp.Aggregate.new()

iex(2)> :ok = MyApp.Aggregate.evaluate(%Maestro.Types.Command{aggregate_id: id, type: "increment_counter", data: %{}})

iex(3)> {:ok, %{"value" => 1}} = MyApp.Aggregate.get(id)

```