README

Plain php event store implementation for easy persistence by utilizing event sourcing.

It provides classes to express object state changes as events and store them in file based eventstreams.

Installation

You can install mad654/php-event-store via composer by adding "mad654/php-event-store": "dev-master" as requirement to your composer.json.

By Example

For a full working example take a look at src/example. In your vagrant box you can use it like this:

# create storage folder
mkdir -p /tmp/var/eventstore-example/ 

# create a new instance of LightSwitch with id 'kitchen'
src/example/bin/console.php init kitchen

# switch on/off on 'kitchen'
src/example/bin/console.php switch kitchen --on
src/example/bin/console.php switch kitchen --off

# render history of 'kitchen'
src/example/bin/console.php history kitchen

Step by step

Let's take this little example to get in touch with all the new stuff. Lets asume you want to control the light in your Kittchen and for this you have build some switch. All you need is an object which can control the state and keeps its current state over mutlitple requests:

class LightSwitch {	
    private $state = false;
    
    public function isOn(): bool {
        return $this->state;
    }
    
    public function switchOn()
    {
        if ($this->state === true) return;
        // do some stuff which does the hard work
        $this->state = true;
    }
    
    public function switchOff()
    {
        if ($this->state === false) return;
         // do some stuff which does the hard work
        $this->state = false;
    }
}

This is a good beginning, but now you need a way to persist the state.

EventSourcedObject

Instead of creating a database you can extend your class to implement the EventSourcedObject interface. An EventSourcedObject is simply an object which should be available in his current state in the next request and for this it can publish its events as a stream and can be build from scratch based on the events:

<?php
use mad654\eventstore\Event;
use mad654\eventstore\Event\StateChanged;
use mad654\eventstore\EventSourcedObject;
use mad654\eventstore\EventStream\AutoTrackingEventSourcedObjectTrait;
use mad654\eventstore\SubjectId;

class LightSwitch implements EventSourcedObject
{
    use AutoTrackingEventSourcedObjectTrait;

    /**
     * @var bool
     */
    private $state;

    public function __construct(SubjectId $id)
    {
        $this->init($id, ['state' => false]);
    }

    public function isOn(): bool
    {
        return $this->state;
    }

    public function switchOn(): void
    {
        if ($this->state) return;
        $this->record(new StateChanged($this->subjectId(), ['state' => true]));
    }

    public function switchOff(): void
    {
        if (!$this->state) return;
        $this->record(new StateChanged($this->subjectId(), ['state' => false]));
    }

    public function on(Event $event): void
    {
        $this->state = $event->get('state', $this->state);
    }

}

So instead of changing your member variables directly, you will use events for this, like shown in switchOn. So you will record an event and you will update your state in the on function, which is automatically be called by record function.

If you want to see more details, take a look at the AutoTrackingEventSourcedObjectTrait which should be a good starting point for all your event sourced objects and reduce boilerplate code.

EventSourcedObjectStore

use mad654\eventstore\FileEventStream\FileEventStreamFactory;
use mad654\eventstore\EventObjectStore;

$factory = new FileEventStreamFactory("/tmp/eventstore-example");
$store = new EventSourcedObjectStore($factory);

The EventSourcedObjectStore provides a simple API which allows you to save and load objects which implements the EventEmitter interface:

$store->attach($someEventSourcedObject);
unset($someEventSourcedObject);
$id = StringSubjectId::fromString('id-of-some-object');
$someEventEmitter = $store->get($id);

If '$someEventSourcedObject' was implemented correctly, it should have the equal state - before and after the unset() call.

By definition an EventSourcedObjectStore can only store and retrieve objects by id. Here you can find solutions for searching ...

Event

In this example we use the StateChanged event, in production you should create subclasses of this to express more precisely what happened.

In general events are immutable.

Putting all together

use mad654\eventstore\FileEventStream\FileEventStreamFactory;
use mad654\eventstore\EventObjectStore;

$factory = new FileEventStreamFactory("/tmp/eventstore-example");
$store = new EventSourcedObjectStore($factory);

$switch = new LightSwitch('kitchen');
$store->attach($switch);

Some times later in an other request you want to switch on the light in the kitchen:

$store->get(StringSubjectId::fromString('kitchen'))->switchOn();

And again later you will switch it off again:

$store->get(StringSubjectId::fromString('kitchen'))->switchOff();

And again ...

And now you are wondering why your power bill is so expensive - let's take a look at the history:

$renderer = new ArrayEventStreamRenderer();
$store->get(StringSubjectId::fromString('kitchen'))->history($renderer);
$data = $renderer->toArray();

// use symonfy command style to render a nice table on command line
$io = new SymfonyStyle($input, $output);
$io->table(
    ['nr', 'timestamp', 'event_type', 'id', 'property', 'new_state'],
    $data
);

# nr | timestamp           | event_type   | id       | property | new_state
# 1  | 2018-12-01 18:10:00 | StateChanged | kittchen | state    | on
# 2  | 2018-12-01 18:12:00 | StateChanged | kittchen | state    | off
# 3  | 2018-12-01 19:30:00 | StateChanged | kittchen | state    | on
# 4  | 2018-12-03 18:10:00 | StateChanged | kittchen | state    | off

Development

cd local_develop
vagrant up
vagrant ssh

Inside of the vagrant box:

composer install
make test

mad654 / php-event-store

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