Event Sourcing in Laravel with EventSauce

In this talk we're going to take a look at what Event Sourcing is and how we can integrate it a Laravel application. We'll first briefly go through the theory behind Event Sourcing and after that we'll make use of the EventSauce library to show you a real practical approach at how to set up a basic app with some aggregate roots, some projections and some process managers. To wrap things up we'll go through some tips on how you can leverage Event Sourcing in specific situations.

You'll learn:
- Basic theory about event sourcing
- How to implement it in a Laravel app
- Using the eventsauce/laravel-eventsauce library
- A number of practical benefits you get from an event sourced application

1.  @driesvints  driesvints.com EVENT SOURCING IN LARAVEL EVENT SOURCING IN LARAVEL WITH EVENTSAUCE WITH EVENTSAUCE
2.  @driesvints  driesvints.com WHAT WILL WE BE USING? WHAT WILL WE BE USING? eventsauce/eventsauce eventsauce/laravel-eventsauce (0.1.0) laravel/framework
3.  @driesvints  driesvints.com WHAT IS EVENTSAUCE? WHAT IS EVENTSAUCE? An easy way to introduce event sourcing into PHP projects Designed so storage and queueing mechanisms can be chosen based on your specific requirements It has test tooling, designed to work with an event sourcing mindset By Frank De Jonge (Author of FlySystem)
4.  @driesvints  driesvints.com OUR DOMAIN & PROCESS OUR DOMAIN & PROCESS    
5.  @driesvints  driesvints.com MODEL =/= ELOQUENT MODEL MODEL =/= ELOQUENT MODEL COMMAND =/= CONSOLE COMMAND COMMAND =/= CONSOLE COMMAND
6.  @driesvints  driesvints.com WHAT IS EVENT SOURCING? WHAT IS EVENT SOURCING?
7.  @driesvints  driesvints.com WELL, IT'S A LITTLE BIT LIKE MAGIC... WELL, IT'S A LITTLE BIT LIKE MAGIC...
8.  @driesvints  driesvints.com eventsauce.io/docs/event-sourcing Event sourcing is a way to model so ware where the emphasis is put on why (and how) things change, rather than focusing on the current state of the applica on.
9.  @driesvints  driesvints.com eventsauce.io/docs/event-sourcing Ac ons performed on the system result in events, which are communicated throughout the system.
10.  @driesvints  driesvints.com eventsauce.io/docs/event-sourcing Regular OOP-style modelling is closely modelled towards the data model. Our code reflects this data-centric view. When we test our code, we assert based on current applica on state.
11.  @driesvints  driesvints.com eventsauce.io/docs/event-sourcing In event sourcing this concept is turned upside-down. The model is constructed using events that describe things that have happened in the past. These events are used to communicate change throughout the system.
12.  @driesvints  driesvints.com COMMAND QUERY RESPONSIBILITY COMMAND QUERY RESPONSIBILITY SEGREGATION (CQRS) SEGREGATION (CQRS) Separate your read model from your write model Easily separate concerns and constraints Goes really well alongside Event Sourcing
13.  @driesvints  driesvints.com WRITE MODEL WITHOUT EVENT SOURCING WRITE MODEL WITHOUT EVENT SOURCING CRUD like opera ons are performed on models which will overwrite any state we currently have in our persistent storage. $pullRequest = PullRequest::create($data); $pullRequest->update($data); $pullRequest->delete();
14.  @driesvints  driesvints.com WRITE MODEL WITH EVENT SOURCING WRITE MODEL WITH EVENT SOURCING Commands are performed which will validate the data based on your business rules. Events are emi ed and saved in an event store. $pullRequest->open(new OpenPullRequest(...)); // emits PullRequestWasOpened $pullRequest->approve(new ApprovePullRequest(...)); // emits PullRequestWasApproved $pullRequest->merge(new MergePullRequest(...)); // emits PullRequestWasMerged
15.  @driesvints  driesvints.com READ MODEL WITHOUT EVENT SOURCING READ MODEL WITHOUT EVENT SOURCING Data needs to be fetched from three individual tables: pull_requests, authors & comments $pullRequest = PullRequest::with('author', 'comments') ->find($id); $author = $pullRequest->author; $comments = $pullRequest->comments;
16.  @driesvints  driesvints.com READ MODEL WITH EVENT SOURCING READ MODEL WITH EVENT SOURCING Instead of modelling for mul ple use-cases, you model your reads for their specific use-case. Data can be fetched from only one table: pull_requests $pullRequest = PullRequest::find($id); $author = $pullRequest['author']; $comments = json_decode($pullRequest['comments'], true);
17.  @driesvints  driesvints.com READS BECOME EASIER READS BECOME EASIER WRITES BECOME HARDER WRITES BECOME HARDER
18.  @driesvints  driesvints.com EVENT SOURCING... EVENT SOURCING... ...MAKES THE EASY THING HARD ...MAKES THE EASY THING HARD ...BUT MAKES THE HARD THING EASY ...BUT MAKES THE HARD THING EASY
19.  @driesvints  driesvints.com HISTORY NEVER CHANGES HISTORY NEVER CHANGES NO MATTER WHAT NO MATTER WHAT
20.  @driesvints  driesvints.com
21.  @driesvints  driesvints.com WHY WOULD YOU NEED EVENT SOURCING? WHY WOULD YOU NEED EVENT SOURCING?
22.  @driesvints  driesvints.com COOL STUFF YOU CAN DO COOL STUFF YOU CAN DO ⚡ Lightning Fast Reads ✨ Predict The Future ⏳ Time Travel Audi ng And much more...
23.  @driesvints  driesvints.com WHEN SHOULD YOU USE EVENT SOURCING? WHEN SHOULD YOU USE EVENT SOURCING?
24.  @driesvints  driesvints.com PROCESS MODELLING PROCESS MODELLING Finite flows, complex transi ons and transac ons. eventsauce.io/docs/event-sourcing
25.  @driesvints  driesvints.com AUDIT TRAILS AUDIT TRAILS Cases where audit trails are of paramount importance. eventsauce.io/docs/event-sourcing
26.  @driesvints  driesvints.com WHEN SHOULD YOU NOT USE IT? WHEN SHOULD YOU NOT USE IT? When you have a CMS, CRM, or other CRUD-like systems, maybe you don't need event sourcing.
27.  @driesvints  driesvints.com
28.  @driesvints  driesvints.com HOW DO YOU IMPLEMENT EVENT SOURCING? HOW DO YOU IMPLEMENT EVENT SOURCING?
29.  @driesvints  driesvints.com THE TRADITIONAL STATEFUL WAY THE TRADITIONAL STATEFUL WAY public function store(Request $request) { $user = $request->user(); $pullRequest = $user->pullRequests()->create( $request->only( 'title', 'description', 'origin', 'target' ) ); return redirect( '/laravel/framework/pull/'.$pullRequest->id ); }
30.  @driesvints  driesvints.com THE EVENT SOURCING WAY THE EVENT SOURCING WAY public function store(Request $request) { $this->dispatchNow(new OpenPullRequest( $id = PullRequestId::generate(), // UUID $request->user()->id, $request->get('title'), $request->get('description'), $request->get('origin'), $request->get('target') )); return redirect( '/laravel/framework/pull/'.$id->toString() ); }
31.  @driesvints  driesvints.com USE COMMANDS TO TRANSFER DATA USE COMMANDS TO TRANSFER DATA final class OpenPullRequest { // Properties... public function __construct( PullRequestId $pullRequestId, int $userId, string $title, string $description, string $origin, string $target ) { // Assign dependencies to properties... } }
32.  @driesvints  driesvints.com RETRIEVE AGGREGATEROOT AND HANDLE COMMAND RETRIEVE AGGREGATEROOT AND HANDLE COMMAND use PullRequestAggregateRootRepository as Repository; final class OpenPullRequest { // Properties, constructor and getters... public function handle(Repository $repository): void { $pullRequest = $repository->retrieve( $this->pullRequestId ); $pullRequest->open($this); } }
33.  @driesvints  driesvints.com HOLD ON... THE AGGRE-WHAT? HOLD ON... THE AGGRE-WHAT?
34.  @driesvints  driesvints.com ELOQUENT MODELS VS AGGREGATEROOTS ELOQUENT MODELS VS AGGREGATEROOTS Eloquent Models represent your data model AggregateRoots represent your processes and guard your business rules AggregateRoots can consist of mul ple Aggregates
35.  @driesvints  driesvints.com THE AGGREGATEROOT THE AGGREGATEROOT namespace App\Domain\PullRequest; use EventSauce\EventSourcing\AggregateRoot; use EventSauce\EventSourcing\AggregateRootBehaviour; final class PullRequest implements AggregateRoot { use AggregateRootBehaviour; // ... }
36.  @driesvints  driesvints.com HANDLING THE COMMAND HANDLING THE COMMAND final class PullRequest implements AggregateRoot { public function open(OpenPullRequest $command): void { // Validate business rules... $this->recordThat(new PullRequestWasOpened( $command->userId(), $command->title(), $command->description(), $command->origin(), $command->target() )); } }
37.  @driesvints  driesvints.com VALIDATING BUSINESS RULES VALIDATING BUSINESS RULES final class PullRequest implements AggregateRoot { public function open(OpenPullRequest $command): void { if ($command->origin() === $command->target()) { throw OpenPullRequestFailed::branchesMatch(); } // Record event... } }
38.  @driesvints  driesvints.com RECORDING THE UNHAPPY PATH RECORDING THE UNHAPPY PATH final class PullRequest implements AggregateRoot { public function merge(MergePullRequest $command): void { if ($this->approved === false) { $this->recordThat( new UnapprovedMergeWasAttempted() ); throw MergePullRequestFailed::unapproved(); } // Record event... } }
39.  @driesvints  driesvints.com RECORDING THE EVENT RECORDING THE EVENT trait AggregateRootBehaviour { /** @var object[] */ private $recordedEvents = []; // ... protected function recordThat(object $event) { $this->apply($event); $this->recordedEvents[] = $event; } // ... }
40.  @driesvints  driesvints.com APPLYING EVENTS APPLYING EVENTS trait AggregateRootBehaviour { // ... protected function apply(object $event) { $parts = explode('\\', get_class($event)); $this->{'apply' . end($parts)}($event); $this->aggregateRootVersion++; } // ... }
41.  @driesvints  driesvints.com APPLYING THE EVENT APPLYING THE EVENT Is also run every me the aggregate is retrieved from its repository. final class PullRequest implements AggregateRoot { public function applyPullRequestWasOpened( PullRequestWasOpened $event ): void { $this->userId = $command->userId(); $this->origin = $command->origin(); $this->target = $command->target(); } }
42.  @driesvints  driesvints.com PERSISTING EVENTS PERSISTING EVENTS Excep ons cascade through but events are s ll saved. public function handle(Repository $repository): void { $pullRequest = $repository->retrieve( $this->pullRequestId ); try { $pullRequest->open($this); } finally { $repository->persist($pullRequest); } }
43.  @driesvints  driesvints.com REBUILDING THE AGGREGATE REBUILDING THE AGGREGATE trait AggregateRootBehaviour { public static function reconstituteFromEvents( AggregateRootId $aggregateRootId, Generator $events ): AggregateRoot { $aggregateRoot = new static($aggregateRootId); foreach ($events as $event) { $aggregateRoot->apply($event); } return $aggregateRoot; } }
44.  @driesvints  driesvints.com THE EVENT STORE THE EVENT STORE Schema::create('domain_messages', function (Blueprint $table) { $table->bigIncrements('id'); $table->string('event_id', 36); $table->string('event_type', 100); $table->string('aggregate_root_id', 36)->nullable()->index() $table->dateTime('recorded_at', 6)->index(); $table->text('payload'); });
45.  @driesvints  driesvints.com EVENT STORES EVENT STORES Append- & Read-Only Can live outside the main system Can live independently by AggregateRoot The only part that you cannot lose!
46.  @driesvints  driesvints.com DOMAIN MESSAGES DOMAIN MESSAGES Events are transported in Domain Messages and are saved in an event store Messages contain the event (payload), aggregate root id, recorded mestamp Event payload is serialized before stored
47.  @driesvints  driesvints.com DISPATCHING MESSAGES DISPATCHING MESSAGES Messages are dispatched by the MessageDispatcher Can be Asynchronous, Synchronous, or both! Messages are handled by Consumers
48.  @driesvints  driesvints.com CONSUMERS CONSUMERS Two types of consumers: Projec ons: processes events to update "read models" Process Managers: listen to events and then perform ac ons
49.  @driesvints  driesvints.com PROJECTIONS PROJECTIONS Used to update read models like: Database tables Report files/pdfs Your search indexes like Algolia, Elas cSearch, ... ...
50.  @driesvints  driesvints.com WHY ARE PROJECTIONS USEFUL? WHY ARE PROJECTIONS USEFUL? Separate presenta onal state from the process you're modelling Read models are free from any constraints your domain model has Your read models can be very op mized this way Create as many read models as you like Super easy to rebuild read models
51.  @driesvints  driesvints.com THE PROJECTION THE PROJECTION use App\Models\PullRequestPage; use EventSauce\EventSourcing\Message; use EventSauce\LaravelEventSourcing\Consumer; final class BuildPullRequestPage extends Consumer { public function handlePullRequestWasOpened( PullRequestWasOpened $event, Message $message ): void { PullRequestPage::create(...); } // Handle other events... }
52.  @driesvints  driesvints.com REBUILDING PROJECTIONS REBUILDING PROJECTIONS Allows you to discard your current state of your read model and rebuild it from its event stream. Unfortunately not baked into EventSauce... ...but maybe in Laravel EventSauce
53.  @driesvints  driesvints.com PROCESS MANAGERS PROCESS MANAGERS Used to react to events: Send email no fica ons Trigger builds Clear logs ...
54.  @driesvints  driesvints.com WHY ARE PROCESS MANAGERS USEFUL? WHY ARE PROCESS MANAGERS USEFUL? Easily handle one- me ac ons Separate mul ple steps for your process Handle non-user interac ons Can be performed in the background and aren't blocking
55.  @driesvints  driesvints.com THE PROCESS MANAGER THE PROCESS MANAGER use EventSauce\EventSourcing\Message; use EventSauce\LaravelEventSourcing\Consumer; final class PullRequestNotifier extends Consumer { public function handlePullRequestWasOpened( PullRequestWasOpened $event, Message $message ): void { Mail::to($maintainer) ->send(new PullRequestWasOpenedMail); } }
56.  @driesvints  driesvints.com TESTING IN A BDD WAY TESTING IN A BDD WAY class MergingPullRequestTest extends PullRequestTestCase { /** @test */ public function it_can_be_merged() { $pullRequestId = $this->aggregateRootId(); $this->given( new PullRequestWasOpened($pullRequestId, ...), new PullRequestWasApproved($pullRequestId) )->when( new MergePullRequest($pullRequestId) )->then( new PullRequestWasMerged() ); } }
57.  @driesvints  driesvints.com TESTING FAILURES TESTING FAILURES /** @test */ public function it_cannot_be_merged_when_not_approved() { $pullRequestId = $this->aggregateRootId(); $this->given( new PullRequestWasOpened($pullRequestId, ...) )->when( new MergePullRequest($pullRequestId) )->then( new UnapprovedMergeWasAttempted() )->expectToFail( new MergePullRequestFailed() ); }
58.  @driesvints  driesvints.com OTHER THINGS EVENTSAUCE CAN DO OTHER THINGS EVENTSAUCE CAN DO Generate Commands and Events from yaml Message decora on to add metadata to your messages Event versioning (handling concurrency)
59.  @driesvints  driesvints.com
60.  @driesvints  driesvints.com WHAT ABOUT PERFORMANCE? WHAT ABOUT PERFORMANCE?
61.  @driesvints  driesvints.com ONE QUERY TO RETRIEVE ALL EVENTS ONE QUERY TO RETRIEVE ALL EVENTS use EventSauce\EventSourcing\MessageRepository; class LaravelMessageRepository implements MessageRepository { public function retrieveAll(AggregateRootId $id): Generator { $payloads = $this->connection->select(' SELECT payload FROM domain_messages WHERE aggregate_root_id = ? ORDER BY recorded_at ASC ', [$id->toString()]); // Unserialize here and return by "yield"... } }
62.  @driesvints  driesvints.com PERFORMANCE PERFORMANCE Objects usually don't live long enough for it to be a problem One query to retrieve all events from an aggregate In-memory event replaying is quite fast actually Use snapsho ng when you really need it (millions of events on a single aggregate)
63.  @driesvints  driesvints.com TIME TRAVEL TIME TRAVEL ⏳ ⏳
64.  @driesvints  driesvints.com REVISIT YOUR APP IN THE PAST REVISIT YOUR APP IN THE PAST Replay events un l a certain me Only projec ons are replayed Combine with your VCS to also show the app code from that me Neat for debugging, demo'ing, etc
65.  @driesvints  driesvints.com HOW DO I START USING EVENT SOURCING HOW DO I START USING EVENT SOURCING IN AN EXISTING SYSTEM? IN AN EXISTING SYSTEM?
66.  @driesvints  driesvints.com USING EVENT SOURCING IN AN EXISTING SYSTEM USING EVENT SOURCING IN AN EXISTING SYSTEM Start with a simple process Make sure you have your process modelled first (use Event Storming) Introduce a "start event" with all of your current data Don't try to be smart and "guess" the past events because you'll fail miserable
67.  @driesvints  driesvints.com READING MATERIAL READING MATERIAL eventsauce.io/docs/event-sourcing eventsauce.io/docs/architecture eventsauce.io/docs/lifecycle michielrook.nl verraes.net
68.  @driesvints  driesvints.com OTHER LIBRARIES OTHER LIBRARIES github.com/spa e/laravel-eventsauce github.com/spa e/laravel-event-projector
69.  @driesvints  driesvints.com THANKS! THANKS!  driesvints.com  @driesvints fullstackbelgium.be fullstackeurope.com