CQRS

A foundational package for Command Query Responsibility Segregation (CQRS) compatible with Laravel.

Table of Contents

• Installation
  • Peer Dependencies
  • Framework Helpers Functions
• Usage Guide
  • Commands
    • How to Create a Command
    • How to Run a Command
    • How to Create an Evented Command
    • How to Run a Command in a Transaction
    • How to Use a Command as an Event Handler
    • How to Queue a Command as a Job
    • How to Run a Command on a Queue as a Job
    • How to Invalidate Queries from Commands
  • Queries
    • How to Create a Query
    • How to Get Query Results
    • How to Create an Evented Query
    • How to Create a Cached Query
    • How to Bust a Cached Query
  • Events
    • How Auto-resolution of Events Work
    • How to Customize the Before and After Events
    • Recommended Conventions for Command and Event Naming
  • Concerns
    • Using CQRS in Your Classes
    • Using Argument Validators
    • Using Option Defaults
    • Saving Models Within Commands
    • Using the Silencer
  • Extending
    • Using Macros on the Builder
    • Using Mixins on the Builder
• Running the Tests
• Licensing

Installation

The package installs into a PHP application like any other PHP package:

composer require artisansdk/cqrs

Peer Dependencies

This package has some peer dependencies on Laravel packages. Rather than depending on the entire framework, it is up to the developer to meet the peer dependencies if the dependent features are going to be used. While Laravel does provide out the box packages for these dependencies, if you install outside of Laravel then you may need to configure your application to implement the dependent interfaces.

The following explains which packages you should additionally install should you need the corresponding features outside of Laravel:

• illuminate/container: An IoC container must be provided by the framework and injected into the ArtisanSdk\CQRS\Dispatcher. Laravel will do this automatically via a typehinted interface in the constructor, but the Dispatcher technically relies directly on Illuminate\Container\Container if you use Dispatcher::make() manually or rely on Command::make() or similar static functions.

• illuminate/bus: Queueable jobs that get chained rely upon a command bus within Laravel. While not strictly needed, if you intend to do sophisticated queueing then you will need this peer dependency for the actual job dispatching. See also Framework Helper Functions.

• illuminate/events: Using the ArtisanSdk\CQRS\Buses\Transaction command wrapper will require this package which ships with Laravel. Essentially the dependency relies on the ability for the framework to dispatch the events to the framework layers and back down to the CQRS package level.

• illuminate/database: Using the ArtisanSdk\CQRS\Buses\Transaction or ArtisanSdk\CQRS\Query classes will require this database package to provide database transactions and querying statements.

• illuminate/pagination: Using ArtisanSdk\CQRS\Query::paginate() method will require the use of this package to return the paginated results.

• illuminate/queue: Using any queueing functions of the Laravel framework will require this package. This would include any serialization of the models for jobs and events or for interacting with queues from jobs and commands.

• illuminate/validation: You only need to install this peer-dependency if you wish to have arguments passed to queries and command automatically validated against an array of validation rules or against a custom passed validator. The CQRS package provides support for this Laravel validation package but it is not strictly required.

Framework Helper Functions

Laravel includes several helpers.php files which expose global functions that technically any framework could implement. This further decouples this package from Laravel. If this package is therefore use outside of Laravel you will need to implement these helpers (much like this package did for testing purposes):

• app() is used to resolve dependencies to make static calls like Command::make() able to auto-resolve commands out of an IoC container. When passed a string that references a class name bound in the container, the function should return a built instance of that class.

• dispatch() is used primarily used by chainable, queued commands via the ArtisanSdk\CQRS\Concerns\Queueable trait helper dispatchNextJobInChain(). The function should accept a class and pass it along the framework's command bus. For Laravel-based applications this can be met by installing illuminate\bus which provides Illuminate\Bus\Dispatcher as the command bus.

Usage Guide

Commands

A command implements the ArtisanSdk\Contract\Runnable interface which makes it both invokable and runnable. The intended use of a command is to perform some sort of "write" operation or complete a unit of work and return its results. An asynchronous command would return a promise while a synchronous command would return the result itself or nothing at all.

How to Create a Command

A basic example of using a command is to create a class that extends the ArtisanSdk\CQRS\Command class and implementing the run() method returning whatever value you want after the command is ran. You can use the constructor method to inject any command dependencies. Argument dependencies are implicitly required and the caller must satisfy the requirements or else the developer must throw an exception to ensure all required arguments are passed and validated prior to execution of critical command logic.

namespace App\Commands;

use App\User;
use ArtisanSdk\CQRS\Command;

class SaveUser extends Command
{
    protected $model;

    public function __construct(User $model)
    {
        $this->model = $model;
    }

    public function run()
    {
        $user = $this->model;
        $user->email = $this->argument('email');
        $user->save();

        return $user;
    }
}

How to Run a Command

There are multiple ways to dispatch a command. The first way is to simply create an instance of the ArtisanSdk\CQRS\Dispatcher and then call command() on it which will return an new instance of the command wrapped inside of an arguments builder class. You can then chain any arbitrary arguments onto the command before calling run() or invoking the builder directly. You could also call arguments() on the builder passing an array of arguments.

Run a Command Using the Dispatcher

$user = ArtisanSdk\CQRS\Dispatcher::make()
    ->command(App\Commands\SaveUser::class)
    ->email('[email protected]')
    ->run();

Run a Command Statically

Alternatively you could just make the command statically which will also create an instance of the command builder:

$user = App\Commands\SaveUser::make()
    ->email('[email protected]')
    ->run();

Run a Command From Anywhere

Using ArtisanSdk\CQRS\Concerns\CQRS helper trait on any class (e.g.: a controller) allows you to dispatch commands directly by simply calling $this->dispatch() or $this->command() passing the command's class name as the argument. This will return an instance of the command builder. The base ArtisanSdk\CQRS\Command uses this trait and therefore subcommands can be executed within a command in the same way:

namespace App\Http\Controllers;

use App\Commands\SaveUser;
use App\Http\Controllers\Controller;
use ArtisanSdk\CQRS\Concerns\CQRS;
use Illuminate\Http\Request;

class UserController extends Controller
{
    use CQRS;

    public function post(Request $request)
    {
        return $this->command(SaveUser::class)
            ->email($request->input('email'))
            ->run();
    }
}

Run a Command Manually (Without the Command Bus)

Commands executed like the above examples all end up routing the command through the dispatcher which implements a basic command bus for a few support scenarios that many command-based applications need including eventing, queueing, and transactions. While you can and probably should always dispatch a command, you can also manually execute a command by simply constructing it either using auto-resolution from the container or manually and then calling the run() method on the command or directly invoking the class:

$user = (new App\Commands\SaveUser(new App\User))
    ->arguments([
        'email' => '[email protected]',
    ])
    ->run();

This will bi-pass the command bus setup by the dispatcher and therefore skip any added wrapper functionality the dispatcher offers.

How to Create an Evented Command

Sometimes you want the rest of your code to be made aware of the processing of a particular command. You may want to execute some code before the command or after the command based on the result of the command. Using the dispatcher this is trivially done by simply implementing the ArtisanSdk\Contract\Eventable interface on any command that should be evented:

namespace App\Commands;

use App\User;
use ArtisanSdk\Contract\Eventable;
use ArtisanSdk\CQRS\Command;

class SaveUser extends Command implements Eventable
{
    protected $model;

    public function __construct(User $model)
    {
        $this->model = $model;
    }

    public function run()
    {
        $user = $this->model;
        $user->email = $this->argument('email');
        $user->save();

        return $user;
    }
}

With the addition of the eventable contract implemented, an event will be fired before and another after the command is ran. The before event will be given the arguments passed to the command while the after event will be given the results of the command itself. The event fired is an instance of ArtisanSdk\CQRS\Events\Event.

Silencing an Evented Command

While firing events before and after a command is executed can be useful, sometimes you want to run an evented command silently so listeners are not fired. Evented commands have helper methods on the command and also the command builder to make this use case easier. You can call silence() to silence the command, silenced() to check if a command is silenced, and silently() to run silently.

$user = App\Commands\SaveUser::make()
    ->email('[email protected]')
    ->silently();

How to Run a Command in a Transaction

Often you'll create a command that performs multiple database writes to different tables or multiple records. Alternatively you may have a command that executes multiple subcommands and there needs to be a certain level of atomicity relating the command's overall execution. If a sucommand or secondary write fails, you'll want to roll back the command. This boilerplate logic is annoying to have to write into each command so this package provides a trivial way to do this by implementing the ArtisanSdk\Contract\Buses\Transactional interface on any command that should be transactional:

namespace App\Commands;

use ArtisanSdk\Contract\Buses\Transactional;
use ArtisanSdk\CQRS\Command;

class SaveUser extends Command implements Transactional
{
    protected $model;

    public function __construct(User $model)
    {
        $this->model = $model;
    }

    public function run()
    {
        $user = $this->model;
        $user->email = $this->argument('email');
        $user->save();

        return $user;
    }
}

Now if for any reason the command throws an exception, the queries executed within the command or subcommands will be rolled back. If everything works as expected then the transactions are committed like normal. The benefit of this approach is that it makes it easy to bypass the transactional model for testing purposes by simply invoking the commands manually which bypasses the transactional wrapper.

Aborting a Transactional Command

Sometimes you want to rollback your transaction without throwing an exception and yet still return a result that satisfies your caller's response expectations. For such cases the command should call abort() and then return the result. The transactional wrapper will still rollback but will not bubble any exception:

namespace App\Commands;

use App\User;
use ArtisanSdk\Contract\Buses\Transactional;
use ArtisanSdk\CQRS\Command;

class ChangePassword extends Command implements Transactional
{
    protected $model;

    public function __construct(User $model)
    {
        $this->model = $model;
    }

    public function run()
    {
        if( ! $user = $this->user($email) ) {
            $this->abort();

            return false;
        }

        $user->password = $this->argument('password');
        $user->save();

        return $user;
    }

    protected function user() : User
    {
        return $this->model
            ->where('email', $this->argument('email'))
            ->first();
    }
}

The above example changes the password of the user that matches the email address. If the email does not match any known user, rather than throwing an exception, we just abort and return false instead. Had we performed any other write queries then those would have been rolled back.

Silencing After Events With Abort

The main benefit of aborting a command however is that the after events are not fired if the command is aborted. This is handy when a command is actually queued as a job and the job has already been handled or is no longer needed and therefore should not fire an exception and risk being marked as a failed job but can instead simply be aborted and still be treated as a successful job by the worker. Imagine for example that an email was queued to be sent out 15 minutes later but within that 15 minutes an action occurred that would make such an email irrelevant or redundant: then when the command is being executed as a queued job to send the email out, a pre-check could be performed to determine if the command should still be ran and if not, the command could be aborted.

Checking If a Command Was Aborted

The abort() and aborted() methods are public methods of the command and can also be used in circumstances where you might want to abort multiple commands in a command pool based on when one command in the pool is aborted. You can also use the aborted() method to check if a command has been aborted to better determine what to do with the command's result.

How to Use a Command as an Event Handler

When the application fires events, event subscribers can broadcast the event to all bound event listeners. Each listener provides a handle() method which receives the event as argument and then executes some arbitrary logic. This handler is essentially the same as a command and therefore commands can be used as command handlers. The default behavior of handle() is to extract the payload property from the event object and pass that as arguments to a command builder and then self-execute by invoking the command's run() method.

First you'll need to create a custom event that should fire. These events need to extend ArtisanSdk\CQRS\Events\Event which provides the payload of arguments that will be passed to the command. In our example event we accept a type hinted App\User model as the only argument to the constructor to ensure that the event is created with the right kind of payload. We then assign this model to the user key in an array that is passed to the parent constructor. This parent will correctly assign to this argument to the payload property.

namespace App\Events;

use App\User;
use ArtisanSdk\CQRS\Events\Event;

class UserSaved extends Event
{
    protected $user;

    public function __construct(User $user)
    {
        $this->user = $user;
    }
}

Next, we'll need to create a command that fires this event when it is done running. For a non-conventional event name, you'll need to provide the dispatcher with the custom event name in the beforeEvent() and afterEvent() methods of the command. In our case we just return the class name as a string which the dispatcher will construct and pass the App\User returned by run() to the event's constructor.

namespace App\Commands;

use App\Events\UserSaved;
use ArtisanSdk\Contract\Eventable;
use ArtisanSdk\CQRS\Command;

class SaveUser extends Command implements Eventable
{
    protected $model;

    public function __construct(User $model)
    {
        $this->model = $model;
    }

    public function run()
    {
        $user = $this->model;
        $user->email = $this->argument('email');
        $user->save();

        return $user;
    }

    public function afterEvent()
    {
        return UserSaved::class;
    }
}

While the dispatcher handles all the indirection automatically, it can be summarized as having accomplished the same as manually constructing and calling the following:

$command = (new App\Commands\SaveUser(new App\User()));
$builder = new ArtisanSdk\CQRS\Builder($command);
$user = $builder->email('[email protected]')->run();
$event = new App\Events\UserSaved($user);

Next we'll need create another command which we will bind as the event handler for any App\Events\UserSaved events that are fired:

namespace App\Commands;

use ArtisanSdk\CQRS\Command;

class SendUserWelcomeEmail extends Command
{
    public function run()
    {
        $user = $this->argument('user');

        // ... the $user is an instance of `App\User` and can be used in a Mailable
    }
}

The actual logic of sending the email has been omitted but as you can see it is possible to get the App\User model from the arguments that will be automatically passed to the command when the handle() method is called. This is accomplished by simply wiring up a listener. It's recommended that you follow Laravel's documentation on wiring up listeners within the App\Providers\EventServiceProvider class using the $listen property but the following demonstrates manually subscribing a event handler to an event as an event listener:

event()->listen(App\Events\UserSaved::class, App\Commands\SendUserWelcomeEmail::class);

Now whenever the App\Events\UserSaved event is fired the App\Commands\SendUserWelcomeEmail command's handle() method will be called with the event passed as argument. This in turn will unwrap the event and provide the event's payload as arguments to the command and then self-execute. Firing the event is the equivalent of manually calling:

$command = (new App\Commands\SaveUser(new App\User()));
$builder = new ArtisanSdk\CQRS\Builder($command);
$user = $builder->email('[email protected]')->run();
$event = new App\Events\UserSaved($user);
$handler = (new App\Commands\SendUserWelcomeEmail());
$result = $handler->handle($event);

How to Queue a Command as a Job

In the case above, we're sending an email and this is often considered a background process that is not critical to response success. Usually a queued job would be used in this case. If you think about it though, a job is really just the definition of an event and it's handler which is queued for later execution rather than immediate execution. Since commands can be these self-executing event handlers, the handler can also be queued as a job instead. This package makes it trivial to queue the handler by simply implementing the ArtisanSdk\Contract\CQRS\Queueable interface and adding the ArtisanSdk\CQRS\Concerns\Queues trait on the command you want to be queued and support queue interactions:

namespace App\Commands;

use ArtisanSdk\CQRS\Command;
use ArtisanSdk\CQRS\Triats\Queue;
use ArtisanSdk\Contract\CQRS\Queuable;

class SendUserWelcomeEmail extends Command implements Queueable
{
    use Queues;

    // ... same as before but it'll now be queued
}

Now whenever the App\Events\UserSaved event is fired, the App\Commands\SendUserWelcomeEmail command will be queued and then executed by a queue worker. All the same methods and properties like $connection, $queue, and $delay are supported on the command now and you can therefore configure your commands with defined defaults or let the caller decide via onConnection(), onQueue(), etc.

How to Run a Command on a Queue as a Job

While it's more common to have an event handler be queued since events are by nature asynchronous, some commands also lend themselves to background processing. These commands are not ran but rather queued. So this package makes it trivial to explicitly queue a command that implements ArtisanSdk\Contract\CQRS\Queueable:

$job = App\Commands\SendUserWelcomeEmail::make()
    ->email('[email protected]')
    ->queue();

Instead of calling run() on the command, you simply call queue(). The magic of this method is that the ArtisanSdk\CQRS\Builder class is wrapping the queueable command to pass the arguments to a generic ArtisanSdk\Contract\Event\Event implementation. This event is a polyfill for the real underlying ArtisanSdk\Contract\CQRS\Queueable::queue($event) method.

While the dispatcher handles all the indirection automatically, it can be summarized as having accomplished the same as manually constructing and calling the following:

$job = (new App\Commands\SendUserWelcomeEmail())
    ->queue(new ArtisanSdk\CQRS\Events\Event([
        'email' => '[email protected]',
    ]));

The pending job is returned and the framework dispatcher will push to the queue when the object is destructed. Having access to the job allows for further customization of the job prior to dispatch including calling familiar methods like onConnection, onQueue, delay, and chain.

How to Invalidate Queries from Commands

Documenation in progress. Please excuse the mess and consider contributing a pull request to improve the documentation.

Queries

A query implements the ArtisanSdk\Contract\Query interface which makes it both invokable and runnable, therefore indistinguishable from a command. The intended use of a query is to perform some sort of "read" operation or get a result from a data store. An asynchronous query would return a promise while a synchronous command would block program execution until the result is returned.

How to Create a Query

A basic example of using a query is to create a class that extends the ArtisanSdk\CQRS\Query class. This abstract class forwards __invoke() to run(). The class also includes a shorthand get() method which forwards to run() to make it feel more similar to working with the DB::table()->get() or Eloquent::query()->get() method. implementing the builder() method returning whatever query builder you want to be executed by the get() method. So implementing a run() method that returns query results is all that is necessary to take advantage of the query bus.

You can use the constructor method to inject any query dependencies such as an Eloquent model, a service class, etc. Argument dependencies are implicitly required and the caller must satisfy the requirements or else the developer must throw an exception to ensure all required arguments are passed and validated prior to execution of critical query logic.

Important: While using Eloquent ORM may sanitize or escape arguments, this package makes no assumptions that the arguments passed to the query class are safe. Make sure you validate and sanitize values before executing against the data backend.

The abstract ArtisanSdk\CQRS\Query class actually assumes you are using Laravel's Database ORM and query builder. The run() method therefore calls to an abstract builder() to get the SQL builder. You will need to implement this builder() method or stub it out if you are using, for example a RESTful API as the query backend.

Flat File Implemenation

Assuming you had a resources/lang/en/states.php file containing a PHP array of state abbreviations and names then the following query would be the minimal implementation required. Note that the builder() method is stubbed out to satisfy the parent class's abstract definition. Also note that we do not need to use a database as the results can be loaded from a flat file on the system disk.

namespace App\Queries;

use ArtisanSdk\CQRS\Query;

class GetStates extends Query
{
    public function builder()
    {
        // required to satisfy abstract parent
    }

    public function run()
    {
        return trans('states');
    }
}

Here's how you could call this query to get the states:

$states = App\Queries\GetStates::make()->get();

HTTP API Implemenation

Again instead of a database, you could have your data backed by an HTTP API and use an HTTP client like Guzzle to fetch the results:

namespace App\Queries;

use ArtisanSdk\CQRS\Query;
use GuzzleHttp\Client as Guzzle;

class GeocodeIP extends Query
{
    protected $http;

    public function __construct(Guzzle $http)
    {
        $this->http = $http;
    }

    public function builder()
    {
        // required to satisfy abstract parent
    }

    public function run()
    {
        // Require the argument and validate as an IPv4 address
        $ip = $this->argument('ip', ['ipv4']);

        // Generate a URL to injected with the IP address
        $url = sprintf('https://freegeoip.app/json/%s', $ip);

        // Use Guzzle to get the geocoded response
        $response = $this->http->get($url);

        // Parse the JSON body of the response
        return json_decode($response->getBody()->getContent());
    }
}

In this example we use a dynamic query argument to build up the HTTP request when we make the get() call to execute the request. Remember get() is forwarded to our custom run() implementation so it all just works. Everything you know about how fluently building up command arguments applies to queries as well.

$result = App\Queries\GeocodeIP::make()
    ->ip('104.131.182.33')
    ->get();

echo $result->zip_code; // 07014

Database Implemenation

Back to that builder() method though. As mentioned, the package assumes you will be using Eloquent ORM or at minimum a database abstraction and so the builder() method is intended to be used to return a query builder. Therefore an implementation of a model backed query would look like this:

namespace App\Queries;

use App\User;
use ArtisanSdk\CQRS\Query;

class ListUsers extends Query
{
    protected $model;

    public function __construct(User $model)
    {
        $this->model = $model;
    }

    public function builder()
    {
        $query = $this->model->query();

        $order = $this->option('order', 'id', ['in:id,name,email,created_at,updated_at']);
        $sort = $this->option('sort', 'desc', ['in:asc,desc']);

        $query->orderBy($order, $sort);

        if( $keyword = $this->option('keyword', null, ['string', 'max:64']) ) {
            $this->scopeKeyword($query, $keyword);
        }

        return $query;
    }

    // This method could be called anything, but naming it similar to Eloquent
    // helps clarify the intent of such builder abstractions to protected methods.
    protected scopeKeyword($query, string $keyword)
    {
        $wildcard = sprintf('%%s%', $keyword);

        return $query->where(function($query) use ($wildcard) {
            return $query
                ->orWhere('name', 'LIKE', $wildcard)
                ->orWhere('email', 'LIKE', $wildcard);
        });
    }
}

We don't need to define the run() method because the parent class automatically executes the required $this->builder()->get() call to return the result of the query when we run it. Passing arguments to the query lets you customize the results at call time.

// Get the users with default arguments: sort desc by name
$users = App\Queries\ListUsers::make()->get();

// Get the users using custom arguments which are validated in the builder
$users = App\Queries\ListUsers::make()
    ->order('name')
    ->sort('asc')
    ->keyword('john')
    ->get();

How to Get Query Results

The base query implements get() but also implements the convenient method of paginate().

// Get the ?page=# results of users with only the name and email columns
$paginator = App\Queries\ListUsers::make()->paginate(10, ['name', 'email']);

Furthermore if you need to inspect the query you can call toSql() instead of get() or builder() directly to customize the query further for one-off query executions:

// select * from `users` order by `name` desc
$sql = App\Queries\ListUsers::make()
    ->order('name')
    ->toSql();

// Bypass the run() method and execute against the builder directly
$users = App\Queries\ListUsers::make()
    ->order('name')
    ->builder()
    ->limit(10)
    ->get();

// Customize the builder outside of the query
$query = App\Queries\ListUsers::make();
$query->order('name');
$builder = $query->builder(); // get the builder outside of the query
$builder->whereIn('id', [1, 2, 3]); // a customization to the query
$users = $query->get(); // since $builder is referenced, query executes against customized builder

It is common practice to create base classes to help with common queries involving just one result including expanding the interface to include first() or firstOrFail() among other query execution methods.

namespace App\Queries;

use App\User;
use ArtisanSdk\CQRS\Query;

class FindUserByEmail extends Query
{
    protected $model;

    public function __construct(User $model)
    {
        $this->model = $model;
    }

    public function builder()
    {
        return $this->model->query()
            ->where('email', $this->argument('email', ['email']));
    }

    public function run()
    {
        return $this->builder()->first();
    }

    public function firstOrFail()
    {
        return $this->builder()->firstOrFail();
    }

    public static function find(string $email)
    {
        return static::make()->email($email)->run();
    }

    public static function findOrFail(string $email)
    {
        return static::make()->email($email)->firstOrFail();
    }
}

There are a lot of ways to run this query including:

$user = ArtisanSdk\CQRS\Dispatcher::make()
    ->query(App\Queries\FindUserByEmail::class)
    ->email('[email protected]')
    ->run(); // or get()

$user = App\Queries\FindUserByEmail::make()
    ->email('[email protected]')
    ->get();

// Throw Illuminate\Database\Eloquent\ModelNotFoundException if not found
$user = App\Queries\FindUserByEmail::make()
    ->email('[email protected]')
    ->firstOrFail();

// Returns null if not found
$user = App\Queries\FindUserByEmail::find('[email protected]');

// Throw Illuminate\Database\Eloquent\ModelNotFoundException if not found
$user = App\Queries\FindUserByEmail::findOrFail('[email protected]');

A query can also be executed from within a controller or any service that includes the uses the ArtisanSdk\CQRS\Concerns\CQRS trait:

namespace App\Http\Controllers;

use App\Commands\FindUserByEmail;
use App\Http\Controllers\Controller;
use ArtisanSdk\CQRS\Concerns\CQRS;
use Illuminate\Http\Request;

class UserController extends Controller
{
    use CQRS;

    public function show(Request $request, string $email)
    {
        return $this->query(FindUserByEmail::class)
            ->email($email)
            ->firstOrFail();
    }
}

How to Create an Evented Query

Sometimes you want the rest of your code to be made aware that a particular query was executed. You may want to execute some code before the query or after the query based on the result of the query. Using the dispatcher this is trivially done by simply implementing the ArtisanSdk\Contract\Eventable interface on any query that should be evented:

namespace App\Queries;

use App\Post;
use ArtisanSdk\Contract\Eventable;
use ArtisanSdk\CQRS\Query;

class MostPopularPosts extends Query implements Eventable
{
    protected $model;

    public function __construct(Post $model)
    {
        $this->model = $model;
    }

    public function builder()
    {
        return $this->query()
            ->orderBy('views', 'desc')
            ->take($this->option('limit', 10, 'is_integer'));
    }
}

With the addition of the eventable contract implemented, an event will be fired before and another after the command is ran. The before event will be given the arguments passed to the query while the after event will be given the results of the query itself. The event fired is an instance of ArtisanSdk\CQRS\Events\Event.

As an example use case for the above query, the post authors could be notified that their post is now being featured on the website using an after event handler. Alternatively instrumentation could be started prior to the execution and then captured after in the after event as the elapsed time the query took to execute.

All other event bus behaviors relating to eventable commands also apply to commands. See documentation on eventable commands for more details.

How to Create a Cached Query

Maybe you want the results of a query to be cached since the result does not change very often given the same query arguments. This package makes that a trivial effort by simply implementing ArtisanSdk\Contract\Cacheable and setting a public $ttl property, set in seconds, on the query class. The query bus will handle all the cache key creation and cache busting using the default cache drivers of Laravel.

namespace App\Queries;

use App\Post;
use ArtisanSdk\Contract\Cacheable;
use ArtisanSdk\CQRS\Query;

class MostPopularPosts extends Query implements Cacheable
{
    public $ttl = 60 * 60 * 24 * 7; // 1 week cache

    // ... same logic as above
}

You can also dynamically call ->ttl($seconds) on the query builder to customize the TTL of the cache results when querying. You can customize public $key property to set a custom key for the query but by default the value will be generated based on a hash of the query itself. This makes unique queries cacheable under separate auto-generated keys.

How to Bust a Cached Query

While caching is great, sometimes you need to bypass the cache or clear the cache.

// Get the results and cache them for future query execution
$posts = MostPopularPosts::make()->get();

// Secondary calls return the cached results
$cached = MostPopularPosts::make()->get();

// Bust the cache then get the results
$busted = MostPopularPosts::make()->busted()->get();

// This is shorthand for cache busted results
$busted = MostPopularPosts::make()->fresh();

See the ArtisanSdk\CQRS\Buses\Cached class for more public methods that can be used to customize the query's caching mechanisms including bypassing cache, setting a custom key, using tag based caches, and using a different cache driver. The cache bus is probably the most compelling reason to use the query bus when using an Eloquent model because while Eloquent models are Active Record implementations with lots of query builder capabilities, they don't handle domain argument validation nor caching out of the box and with ease.

Events

How Auto-resolution of Events Work

Event naming follows a convention of conjugating the present imperative tense of the command name into a progressive future tense before event and a past tense after event name. This is handled by the Evented wrapper and specifically by the resolveProgressiveTense() and resolvePastTense() methods. Using a regex mapping between common endings for action verbs, the command name can be transformed fairly reliably. For example "create" becomes "creating" and "created". If no conjugation can be found to map to then the resolver will default to "executing" and "executed" as generic event names.

Help Wanted: If you come across a conjugation case that could use improving please take a look at Evented::$progressiveMap and Evented::$pastMap and submit an issue or pull request with recommended changes for your use case.

The auto-resolution logic is not perfect, so you'll still need to customize your event names from time to time and this package provides that functionality.

How to Customize the Before and After Events

Sometimes you'll use a command name that is non-conventional or is simply hard to conjugate event names for because of the weirdness of the English language. In these cases (and in all cases where explicitness is preferred) you can add the beforeEvent and afterEvent methods to an Eventable command. The following illustrates how to customize the before and after events for a custom event naming convention:

namespace App\Commands;

use App\Events\NewPasswordSet;
use App\Events\ChangingPassword;
use ArtisanSdk\Contract\Eventable;
use ArtisanSdk\CQRS\Command;

class ChangePassword extends Command implements Eventable
{
    public function beforeEvent(array $arguments)
    {
        return ChangingPassword::class;
    }

    public function run()
    {
        $user = $this->argument('user');
        $user->password = $this->argument('password');

        return $this->save($user);
    }

    public function afterEvent($result)
    {
        return NewPasswordSet::class;
    }
}

All it takes to modify the event used is to return the class name for the event as a string. Alternatively if you want to construct the event yourself or need to perform event switching based on the result of the command's execution, then you can inspect the $arguments passed to the before event or the $result passed to the after event and simply return an event object. If you do not compose the event objects yourself then the convention is that the arguments and results are injected into the constructor of the event class referenced.

Again this all illustrates that it's possible to customize the events. In practice it would be recommended instead to follow a simpler naming convention such that the command would be App\Commands\Password\Change and the events would be App\Events\Password\Changing and App\Events\Password\Changed instead.

Recommended Conventions for Command and Event Naming

While you are free to use the beforeEvent() and afterEvent() methods to customize the dispatching of any event to suit a namespace or naming convention of your choice, it is often easier to follow a reasonable convention and let the auto-resolution do its thing. The following is a recommended convention for naming your commands and before and after events using namespacing to delineate the classes:

• Commands should be one word action verbs written in present imperative tense
• Queries can be worded like commands or as a noun that defines the result set
• Events should be progressive tense (before events) and past tense (after events) conjugates of the command name
• Namespaces should be used for uniqueness when multiple classes otherwise have the same name.

These basic rules are further explained below:

Commands should be worded in a present imperative tense following the form of an action. The command should be the action only and the namespace should organize the logical use of the action. For example naming a command that registers the user RegisterUser consider naming it simply Register. The arguments to the command are a name and email and not a user model after all so if anything it would be RegisterWithNameAndEmail and the returned value would be the user model.

Now to distinguish this register command from say registering a team or other domain model, consider using the namespace. You could use App\Commands\User as the name space which results in App\Commands\User\Register which follows a logical grouping of related classes under the App\Commands namespace. Or you could use a service oriented grouping of the class under App\User\Commands\Register which creates a service boundary under the App\User namespace.

Now it follows that query gets something so it likewise is a command but can instead be worded as a more concrete synonym for abstract Query and generic "get" such as App\Queries\User\Find or App\Queries\User\Search. You are after all finding the one user or searching for a collection of users and getting the results of that query. You can also organize under a service boundary like App\User\Queries\Find and App\User\Queries\Search if you rather.

You may also find it more fluent to name your queries based on the result. For example you might want to get the recently registered users as a standard query. This could be App\Queries\User\RecentlyRegistered or App\User\Queries\RecentlyRegistered. You might decide to parametize the column such that it's just Recent instead so then it can be used for recently registered, recently updated, etc. In following this convention you might consider the queries as GetRecentlyRegistered and instead just drop the prefix Get from the queries since the fluent code would be written with get() in the syntax: $this->query(RecentlyRegistered::class)->get().

If a command or query is evented then the events are auto resolved unless customized with the beforeEvent() and afterEvent() methods. To help auto-resolution of events, first make sure that the command is a single action word such as Create, Register, Modify, etc. Again make sure it's worded in the present tense. Since a before event is indicative of something about to happen, or in an async system that is happening, it makes sense that before events are transformed from the present tense command name to a progressive tense event name. So the Register command fires a Registering event when it starts.

Furthermore when the command is done, the action is complete and the after event should therefore represent what happened. The after events are transformed from the present tense command name to a past tense event name. So the Register command fires a Registered event when it is done. The same goes for strange commands like Modify which transforms into before and after events of Modifying and Modified. The auto-resolution logic works pretty well but doesn't always get the event names right so always log your events during development to verify what is being fired and that your commands are firing the right events.

Sometimes you'll have awkward command names like App\Commands\User\SetStatus. While you could try to figure out how to namespace it such that the command were App\Commands\User\Status\Set that often leads to unnecessary and artificial expansion of the code base in a way the domain doesn't really care about. Plus auto-resolution will get the past tense sort of wrong with Setted anyways. Commands like SetStatus are still worded in the present tense and so the natural progressive tense event name would be SettingStatus and the past tense event would be StatusSet. As you can see the before event conjugates the verb and keeps it in front of the noun, while the after event places it after the noun. The weirdness of English makes the past and present tense verb form of "set" the same and that is something auto-resolution cannot work out. Therefore you'll need to define these events if needed yourself using beforeEvent() and afterEvent() methods on your command.

A past event can therefore become argument to another command such that domain logic can be encoded with "When [past event] then [present command]" rules. For example, "When user registered then send activation email". This aids in understanding that just because an event has been fired (e.g.: user registered) doesn't mean that the command handler for the event (e.g.: send activation email) has to be executed immediately. This delayed or deferred (technically queued) command still takes the past event payload as present argument to it's own deferred execution. It is therefore possible to completely ignore the return value of a command and build an evented system that relies on the after events instead of the command responses to continue program execution in an async style.

You may also find that you would prefer to name the actual root or aggregate model simply Model which then requires further separation of the namespace to indicate which model it is. For example instead of App\User you might organize as App\Models\User or App\User\Models\User. When you have a lot of models however it can be hard to see where the service boundary is between the User model aggregate and all the related models. Therefore it would be better to organize as App\Models\User\User and to remove the redundancy for User simplify to App\Models\User\Model. In the App\User\Models case the aggregate and all related models are organized under the App\User\Models service boundary so the only reason to rename App\User\Models\User to App\User\Models\Model is to highlight that that model is the root aggregate for the App\User service boundary.

Using a logical grouping of classes into namespaces (a common web app architecture convention) would look like:

App
├─ Commands
    └─ User
        └─ Register
├─ Events
    └─ User
        ├─ Registered
        └─ Registering
├─ Models
    └─ User
        └─ Model
└─ Queries
    └─ User
        ├─ Find
        └─ Search

Alternatively a grouping of classes into namespaces around the service boundary (a service-oriented architecture convention) would look like:

App
└─ User
    ├─ Commands
        └─ Register
    ├─ Events
        ├─ Registered
        └─ Registering
    ├─ Models
        └─ Model
    └─ Queries
        ├─ Find
        └─ Search

This package doesn't care how you organize things but you might find that organizing into service boundaries will help reduce naming and organizing decisions and give you clean separation for later service packaging.

Concerns

The package's primary functionality is exposed as a set of base classes but these classes are composed from a set of base traits. You can use these traits directly in your application code even where CQRS may not be fully needed but the traits prove to be a useful and consistent API for your application.

Using CQRS in Your Classes

ArtisanSdk\CQRS\Concerns\Arguments is a trait that provides arguments and options to a class including all the relevant validation logic and default resolvers. The public methods of the trait are:

• Arguments::arguments($arguments) to get or set the arguments fluently
• Arguments::argument($name, $validator) to get an argument and validate it
• Arguments::option($name, $default, $validator) to get an optional argument and provide a default
• Arguments::hasOption($name) to check if the optional argument is present

ArtisanSdk\CQRS\Concerns\CQRS is the trait that provides the main interactive API for the CQRS pattern. This is the trait that is typically included on a controller, console command, or other class in order to directly dispatch commands using the command builder and dispatcher. The usable methods (most are protected) of the trait are:

• CQRS::dispatcher() gets an instance of the Dispatcher. Instances are not singletons so every command that is dispatched is ran through an unique dispatcher (command bus). This is typically used like $this->dispatcher()->dispatch($class)->run() to compose the runnable class then run it. It can also be used to dynamically forward events like $this->dispatcher()->creating($user) which will fire a Creating event with the user as argument.
• CQRS::call($class, $arguments) directly composes then runs the class with the passed arguments.
• CQRS::command($class) to compose a command using the dispatcher but not run it (use call() instead).
• CQRS::query($class) to compose a query using the dispatcher but not run it (use call() instead).
• CQRS::event($event, $payload) to compose an after event with the payload and fire it using the dispatcher.
• CQRS::until($event, $payload) to compose a before event with the payload and fire it using the dispatcher.

ArtisanSdk\CQRS\Concerns\Handle is a trait that can be used by commands to implement the ArtisanSdk\Contract\CQRS\Handler interface such that an event object may be passed to the handle() method of a command and the command be ran through the command dispatcher using the properties of the event as the arguments. Additionally if the command is queueable then the execution of the command will be deferred as a queued job instead. When the job is resolved out of the queue, the command will be directly invoked, bypassing the handler yet still using the event properties as arguments.

ArtisanSdk\CQRS\Concerns\Queues is a wrapper trait for Laravel compatibility of making an event or command behave like a queued job. It also lets the command interact with the command much like a queued job can. The intended use for this trait is to make the class it is used on a queuable job. See Laravel's documentation on how to customize properties such as $connection, $queue, and $delay or to perform chaining of commands as queued jobs.

ArtisanSdk\CQRS\Concerns\Save is a trait that helps with saving of Eloquent models, especially self-validating models like artisansdk\model provides. It simply provides a save($model) public method which ensures that the model is saved or throws an exception and if saved will return the saved model. See also Saving Models Within Commands.

ArtisanSdk\CQRS\Concerns\Silencer is a trait that the prevents the firing of events when a command or query is ran. The public methods of the trait are:

• Silencer::silence(): set the silence flag on the command so that events are not fired.
• Silence::silenced(): a boolean check to see if the command is silenced. This is used by the evented command wrapper to determine if events should be fired.
• Silence::silently(): a shorthand method for $command->silence()->run() such that you can silently run a command with just $command->silently().

Using Argument Validators

Commands and queries that require arguments often have a lot of boilerplate code that handles validating the values of the arguments passed. To abstract this away, the package includes a simple way to inline common validators and pass more domain-specific validators using callables. You can use a simple closure that returns a boolean value, a class or interface name to check the argument matches, an array of Laravel validation rules for the argument, or a pre-built Laravel validator instance.

namespace App\Commands;

use App\Invoice;
use App\Coupon;
use ArtisanSdk\CQRS\Command;
use Illuminate\Validation\Factory as Validator;

class CalculateInvoice extends Command
{
    public function run()
    {
        // Validate the argument is simply set with a non empty value
        $number = $this->argument('number');

        // Validate the argument matches the Invoice class
        $invoice = $this->argument('invoice', Invoice::class);

        // Validate the argument against a rule of validation rules...
        $subtotal = $this->argument('subtotal', ['integer', 'min:0'])

        // ...or construct it manually yourself for something more complicated
        $subtotal = $this->argument('subtotal', Validator::make($this->arguments(), [
            'subtotal' => ['integer', 'min:0', 'lte:total'],
        ]));

        // Validate the argument against a custom callable...
        $coupon = $this->argument('coupon', function(string $code, string $argument) {
            return $this->couponExists($code, $argument);
        });

        // ... or just reference a method on a callable class
        $coupon = $this->argument('coupon', [$this, 'couponExists']);
    }

    public function couponExists(string $code, string $argument)
    {
        return Coupon::where('code', $code)->exists();
    }
}

Using Option Defaults

The following code demonstrates the use of an option instead of an argument. Based on the presence of the option alone (a flag essentially) you could perform some guarded code or based on explicit check of the option's value if present. In the following example, the default behavior if the option is not set is that the invoice is not saved:

namespace App\Commands;

use App\Invoice;
use ArtisanSdk\CQRS\Command;

class CalculateInvoice extends Command
{
    public function run()
    {
        $invoice = $this->argument('invoice', Invoice::class);

        if( $this->hasOption('save') && true === $this->option('save')) {
            $invoice->save();
        }

        return $invoice;
    }
}

The default value for an option is null by default. You can also set an explicit default value for an option that is not present in the list of arguments. This is demonstrated below using the same example as above. The result is that the invoice is always saved unless explicitly set to false.

namespace App\Commands;

use App\Invoice;
use ArtisanSdk\CQRS\Command;

class CalculateInvoice extends Command
{
    public function run()
    {
        $invoice = $this->argument('invoice', Invoice::class);

        if( $this->option('save', true) ) {
            $invoice->save();
        }

        return $invoice;
    }
}

Occasionally you will want to perform some logical work that is more expensive when an option is not set and the default value needs to be resolved. For example you may want to default to the authenticated user when no user is passed to a command or query as an option. In Laravel this incurs a hit agains the database which is considered expensive and unnecessary if the default option is not actually used. Therefore it's preferred to defer this expensive work. This package supports a resolver callable for the default option which ensures that the work is lazily deferred until indeed the default is needed.

namespace App\Commands;

use App\Invoice;
use App\User;
use ArtisanSdk\CQRS\Command;

class CalculateInvoice extends Command
{
    public function run()
    {
        $invoice = $this->argument('invoice', Invoice::class);

        // This is wasteful since you have to resolve the user even when not used
        // $editor = $this->option('editor', auth()->user());

        // Resolve the authenticated user as the default using a closure...
        $editor = $this->option('editor', function(string $option) {
            return auth()->user();
        });

        // ... or just reference a method on a callable class
        $editor = $this->option('editor', [$this, 'resolveUser']);

        $invoice->editor()->associate($user);

        $invoice->save();

        return $invoice;
    }

    public function resolveUser(string $option) : User
    {
        return auth()->user();
    }
}

Saving Models Within Commands

If you use the ArtisanSdk\CQRS\Concerns\Save trait or the ArtisanSdk\CQRS\Command which includes this trait, then you can quickly save Eloquent models including self-validating models like those provided by artisansdk\model. Simply call save() from within the command or controller and pass in the model that should be saved. If the model does not save because it cannot be validated, then an exception will be raised. If the model can be saved then the saved instance is returned. The use of this helper trait can streamline commands considerably and ensure that saves are being performed consistently.

namespace App\Commands;

use ArtisanSdk\CQRS\Command;

class CalculateInvoice extends Command
{
    public function run()
    {
        $invoice = $this->argument('invoice');
        $invoice->total = 100;

        return $this->save($invoice);
    }
}

In addition to simply saving the models, the trait also formats the errors for CLI applications like Artisan commands and PHPUnit so they are more readable.

Using the Silencer

Sometimes you just don't want your evented commands to fire events. As an example, say that you were sending out an email using SendPasswordResetEmail command which is normally triggered by the UserPasswordReset event. Let's say however that during user registration, the ResetUserPassword command is called and yet you do not want to send out the normal email for password resets. Instead you wish to trigger the logic of resetting a password for an account and instead use SendAccountActivationEmail command to send an account activation in response to UserRegistered event. This is all possible using the ArtisanSdk\CQRS\Concerns\Silencer trait which is already used by the base ArtisanSdk\CQRS\Command class.

In order to accomplish the above example you might write the following:

namespace App\Commands;

use App\User;
use App\Commands\ResetUserPassword;
use App\Events\UserPasswordReset;
use App\Events\UserRegistered;
use ArtisanSdk\CQRS\Command;
use ArtisanSdk\Contract\Eventable;

class RegisterUser extends Command implements Eventable
{
    protected $user;

    public function __construct(User $user)
    {
        $this->user = $user;
    }

    public function run()
    {
        $user = new User();
        $user->email = $this->argument('email');
        $this->save($user);

        return $this->command(ResetUserPassword::class)
            ->user($user)
            ->silently();
    }

    public function afterEvent()
    {
        return UserRegistered::class;
    }
}

class ResetUserPassword extends Command implements Eventable
{
    public function run()
    {
        $user = $this->argument('user');
        $user->password = null;

        return $this->save($user);
    }

    public function afterEvent()
    {
        return ResetUserPassword::class;
    }
}

Extending

Using Macros on the Builder

In the App\Providers\AppServiceProvider@boot (a Laravel default location):

ArtisanSdk\CQRS\Builder::macro('attempt');

Now you can call attempt() on any invokable that supports the method and any arguments passed will be forwarded.

The ArtisanSdk\CQRS\Builder::macro() method supports a second argument however that accepts a callable or closure. Closures passed have $this bound into the context of the builder and therefore behave exactly as if they were a method on the builder already with access to other protected methods of the builder such as forwardToBase(). You can therefore customize the builder using closure based macros:

ArtisanSdk\CQRS\Builder::macro('attempt', function(...$arguments) {
    try {
        return $this->run();
    } catch (Exception $error) {
        throw new App\Exceptions\Error(sprintf($arguments[0], $error->getMessage()));
    }
});

From your app code you would then be able to attempt execution of any command and return a contextual exception without writing ugly try/catch logic everywhere:

$user = App\Commands\SaveUser::make()
    ->email('[email protected]')
    ->attempt('User could not be saved: %s');

Using Mixins on the Builder

Documenation in progress. Please excuse the mess and consider contributing a pull request to improve the documentation.

Running the Tests

The package is unit tested with 100% line coverage and path coverage. You can run the tests by simply cloning the source, installing the dependencies, and then running ./vendor/bin/phpunit. Additionally included in the developer dependencies are some Composer scripts which can assist with Code Styling and coverage reporting:

composer test
composer watch
composer fix
composer report

See the composer.json for more details on their execution and reporting output. Note that composer watch relies upon watchman-make. Additionally composer report assumes a Unix system to run line coverage reporting. Configure the command setting the value for min = 80 to set your minimum line coverage requirements.

Licensing

Copyright (c) 2018-2019 Artisans Collaborative

This package is released under the MIT license. Please see the LICENSE file distributed with every copy of the code for commercial licensing terms.