Loïc Faugeron Technical Blog

In this series we're building the software of a Mars Rover, according to the following specifications. It will allow us to practice the followings:

• Monolithic Repositories (MonoRepo)
• Command / Query Responsibility Segregation (CQRS)
• Event Sourcing (ES)
• Test Driven Development (TDD)

Up until now, we've implemented the first use case, "Landing a rover on Mars":

Mars Rovers need first to be landed at a given position. A position is composed of coordinates (x and y, which are both integers) and an orientation (a string being one of north, east, west or south).

In order to do so, we've:

• created a navigation package
• created LandRover for input validation
• refactored it by:
  • extracting Coordinates
  • extracting Orientation
• created LandRoverHandler for the actual logic

In the last article, we wrote some Event Sourcing code:

• Event, a Data Transfer Object (DTO) that contains the name and the data
• AnEventHappened, which is actually an Event factory
• EventStore, a service responsible for "logging" Events

In this article, we're going to extract them from the navigation package and put them in their own event-sourcing package.

Creating the event-sourcing package

We can start by creating the directory:

git checkout -b 3-event-sourcing
mkdir -p packages/event-sourcing
cd packages/event-sourcing

Composer needs us to set up the package by creating a composer.json file:

{
    "name": "mars-rover/event-sourcing",
    "license": "MIT",
    "type": "library",
    "description": "Mars Rover - Event Sourcing",
    "autoload": {
        "psr-4": { "MarsRover\\EventSourcing\\": "src/MarsRover/EventSourcing" }
    },
    "require": {
        "php": "^7.0"
    },
    "require-dev": {
        "memio/spec-gen": "^0.6"
    }
}

We've decided to use phpspec as a test framework, and to get the most of it we'd like to use its SpecGen extension. To do so we need to create the phpspec.yml.dist file:

extensions:
    Memio\SpecGen\MemioSpecGenExtension: ~

Note: For more information about phpspec see this article.

Finally, we can configure this package's git by creating a .gitignore file:

# Configuration
/phpspec.yml

# Third Party libraries
/vendor/
/composer.lock

With this we've finished creating our package. We can run Composer:

composer install --optimize-autoloader

That should be enough for a second commit:

git add -A
git commit -m '3: Created Event Sourcing package'

Adding event-sourcing to the project

Let's go back to the project's root:

cd ../../

All we need to do is to add a new line in the require section of our composer.json file:

{
    "name": "mars-rover/mars-rover",
    "license": "MIT",
    "type": "project",
    "description": "Mars Rover",
    "repositories": [
        {
            "type": "path",
            "url": "./packages/*"
        }
    ],
    "require": {
        "mars-rover/event-sourcing": "*@dev",
        "mars-rover/navigation": "*@dev",
        "php": "^7.0"
    },
    "require-dev": {
        "phpspec/phpspec": "^3.0@beta"
    }
}

Actually, we also need to add a new section in phpspec.yml.dist:

suites:
    event-sourcing:
        namespace: 'MarsRover\EventSourcing'
        src_path: packages/event-sourcing/src
        spec_path: packages/event-sourcing

    navigation:
        namespace: 'MarsRover\Navigation'
        src_path: packages/navigation/src
        spec_path: packages/navigation

And that's it! We are now able to run Composer and then phpspec:

composer update --optimize-autoloader
vendor/bin/phpspec run

That should be enough for a second commit:

git add -A
git commit -m '3: Added event-sourcing package to main project'

Event Sourcing files

It's now time to move Event Sourcing files from navigation to event-sourcing:

cd packages/event-sourcing
mkdir -p src/MarsRover/EventSourcing
mv ../navigation/src/MarsRover/Navigation/{EventStore.php,Event.php,AnEventHappened.php} ./src/MarsRover/EventSourcing/

We then need to change namespaces:

sed -i 's/Navigation/EventSourcing/g' ./src/MarsRover/EventSourcing/*

To continue those namespace changes we'll have to move back to the navigation package:

cd ../navigation

Then rename the namespaces:

sed -i 's/Navigation\\Event;/EventSourcing\\Event;/g' ./spec/MarsRover/Navigation/*
sed -i 's/Navigation\\EventStore;/EventSourcing\\EventStore;/g' ./spec/MarsRover/Navigation/*
sed -i 's/Navigation\\AnEventHappened;/EventSourcing\\AnEventHappened;/g' ./spec/MarsRover/Navigation/*

We'll also need to add use statements to ./src/MarsRover/Navigation/LandRoverHandler.php:

<?php

namespace MarsRover\Navigation;

use MarsRover\EventSourcing\{
    AnEventHappened,
    EventStore
};

class LandRoverHandler
{
    private $anEventHappened;
    private $eventStore;

    public function __construct(
        AnEventHappened $anEventHappened,
        EventStore $eventStore
    ) {
        $this->anEventHappened = $anEventHappened;
        $this->eventStore = $eventStore;
    }

    public function handle(LandRover $landRover)
    {
        $roverLanded = $this->anEventHappened->justNow(Events::ROVER_LANDED, [
            'x' => $landRover->getCoordinates()->getX(),
            'y' => $landRover->getCoordinates()->getY(),
            'orientation' => $landRover->getOrientation()->get(),
        ]);
        $this->eventStore->log($roverLanded);
    }
}

Since navigation now relies on event-sourcing classes, we need to add it in composer.json:

{
    "name": "mars-rover/navigation",
    "license": "MIT",
    "type": "library",
    "description": "Mars Rover - Navigation",
    "autoload": {
        "psr-4": { "MarsRover\\Navigation\\": "src/MarsRover/Navigation" }
    },
    "repositories": [
        {
            "type": "path",
            "url": "../*"
        }
    ],
    "require": {
        "mars-rover/event-sourcing": "*@dev",
        "php": "^7.0"
    },
    "require-dev": {
        "memio/spec-gen": "^0.6"
    }
}

As we can see, it's quite similar to what we've done in the project's root: we've added a repositories section with the path to packages (../) and then added mars-rover/event-sourcing to the require section, with the version *@dev (any version, including unstable ones).

We are now able to run Composer:

composer update --optimize-autoloader

Let's run the tests:

vendor/bin/phpspec run

All green! We can now succesfully commit our new package:

cd ../../
git add -A
git commit -m '3: Moved Event Sourcing classes to their own package'

Conclusion

We identified AnEventHappened, Event and EventStore as objects that could be in their own package, so we created event-sourcing and moved them in it. This also meant we had to add this package to the project's root and to navigation.

What's next

In the next article, we'll implement AnEventHappened and Event.