ignislabs/flare-cqrs

Flare is a small and easy to use CQRS library.

1.0.0 2017-11-29 03:01 UTC

Requires

• php: >=7.1

Requires (Dev)

• phpspec/phpspec: ^3.2
• psr/container: ^1.0@dev

MIT

• Luciano Longo

README

Flare is a small and easy to use CQRS library.
It drives CQRS by making use of the message bus pattern, separating Queries (interrogatory messages) from Commands (imperative messages).

This library was greatly inspired by Messaging Flavours article by Mathias Verraes.

What is CQRS?

Originated with Bertrand Meyer's Command and Query Separation principle (CQS):

It states that every method should either be a command that performs an action, or a query that returns data to the caller, but not both. In other words, asking a question should not change the answer. More formally, methods should return a value only if they are referentially transparent and hence possess no side effects.

So, Command and Query Responsibility Segregation (CQRS):

... applies the CQS principle by using separate Query and Command objects to retrieve and modify data, respectively.

Source: Wikipedia

Installation

Through composer:

$ composer require ignislabs/flare-cqrs

Usage

FlareCQRS is framework-agnostic, but it's really easy to bootstrap and use.

Bootstrapping

<?php
// Instantiate the resolver:
// This will get you a new instance of the hander based on the _handler id_,
// i.e, the fully-qualified class name, or wharever identifier you might use in
// a framework container.
// By default FlareCQRS comes with two resolvers, a CallableResolver and a PSR11Resolver.
// You can always create your own resolver by implementing the `Resolver` contract.

// Generic callable resolver
$resolver = new \IgnisLabs\FlareCQRS\Handler\Resolver\CallableResolver(function($handlerId) {
    // Somehow resolve your handler handler:
    return new performMagicToGetHandlerInstance($handlerId);
});

// PSR11 resolver (assuming Laravel's `$app` container, since it's PSR-11 compliant)
$resolver = new \IgnisLabs\FlareCQRS\Handler\Resolver\PSR11Resolver($app);

// Now instantiate the buses passing them a Locator instance

$queryBus = new \IgnisLabs\FlareCQRS\QueryBus(
    // Tell the Locator which handler corresponds to which query
    // and how to instantiate the handlers (passing in the Resolver)
    new \IgnisLabs\FlareCQRS\Handler\Locator\MapLocator($resolver, [
        GetAllTasksQuery::class => GetAllTasksHandler::class
    ])
);

$commandBus = new \IgnisLabs\FlareCQRS\CommandBus(
    // Tell the Locator which handler corresponds to which command
    // and how to instantiate the handlers (passing in the Resolver)
    new \IgnisLabs\FlareCQRS\Handler\Locator\MapLocator($resolver, [
        AddTaskCommand::class => AddTaskHandler::class
    ])
);

Usage

Now you can use the buses to dispatch any message, like so:

<?php
// Queries can return whatever you need, it will be encapsulated in a Result object
$result = $queryBus->dispatch(new GetAllTasksQuery('some', 'params'));
// You can call `$result->call`:
$result->call(function(TaskCollection $tasks) {
    // Do what you want with your results
    // Using `call` let's you use type-hinting
    // It can be a any `callable`, not just a closure
});
// Or just get the result right away:
$result->getResult();

// Commands do not return anything
$commandBus->dispatch(new AddTaskCommand('Task Title', 'The task description'));

// You can dispatch multiple commands in sequence with a single call
$commandBus->dispatch(
    new AddTaskCommand('Task Title', 'The task description'),
    new UpdateTaskCommand('NEW Task Title', 'The NEW task description')
);
// Or if you like splat!
$commandBus->dispatch(...$commandsArray);

Message (Query & Command) classes

Your Message classes are simple DTO objects, so there are no rules or contracts to use, they can be whatever you like.

You can, however, take advantage of the DataAccessorTrait. With it you can have automatic accessor properties for your message classes. The trait defines a data private property, a get accessor method and the __get magic method so you can access the data as properties:

<?php

class MyMessage {
    use \IgnisLabs\FlareCQRS\Message\DataAccessorTrait;
 
    public function __construct(string $foo, int $bar) {
        $this->setData(compact('foo', 'bar'));
    }
}

$message = new MyMessage('baz', 'qux');
// Using generic `get` accessor:
$message->get('foo'); // returns 'baz'
// Using the magic accessor:
$message->bar; // returns 'qux'

Handlers

A handler can be anything, as long as it is callable. Although, you will probably want to make them classes. In order to make a class be callable, just implement the __invoke method in it.

The __invoke method will receive an instance of the corresponding command.

This way, the classes are 100% yours, no hard dependency on this library whatsoever and you can typehint freely.

Let's see a quick example:

<?php
class MyMessageHandler {
    public function __invoke(MyMessage $command) {
     // do something here
    }
}

Middlewares

You can create middlewares to interact with the messages before they reach their respective handlers.

Middlewares, same as with the Handlers, are callables, but you might prefer them to be classes, by using the same __invoke strategy.

You can pass your middlewares globally to your buses on instantiation as the last parameters like so:

<?php
$callableMiddleware = function() { /* ... */ };
$queryBus = new \IgnisLabs\FlareCQRS\QueryBus(
    $locator, new LoggingMiddleware($logger), new FooMiddleware, $callableMiddleware
);

Or you can add/replace the middlewares on a one time basis:

<?php
// Add a middleware to the chain
$commandBus->addMiddleware(new LoggingMiddleware($logger));
// Completely replace the middleware chain
$commandBus->middlewares(new LoggingMiddleware($logger), new FooMiddleware);

Buses are immutable, so adding or replacing middlewares on a bus will always return a new bus instance, so any subsequent calls to your buses will not be affected by these middleware changes.