Complex Specifications Pattern in PHP

This package adds support for the Specification pattern in PHP. It helps to leverage complex specification by offloading all the tedious work. Implementing specification pattern is made simpler while leaves all logical wiring to the package.

While framework independent, you can easily integrate this package inside any PHP framework.

System Requirements

You need:

• PHP >= 8.0 but the latest stable version of PHP is recommended

Installation

Use composer:

composer require bakame/spec

or download the library and:

• use any other PSR-4 compatible autoloader.
• use the bundle autoloader script as shown below:

require 'path/to/spec/repo/autoload.php';

use Bakame\Specification\Chain;

$spec = Chain::one(new Rule1())
    ->and(new Rule2(), new Rule3())
    ->orNot(new Rule4());

$spec->isSatisfiedBy($subject);

What is it ?

"the specification pattern is a particular software design pattern, whereby business rules can be recombined by chaining the business rules together using boolean logic. The pattern is frequently used in the context of domain-driven design." -- wikipedia

Usage

Each rule that needs to be satisfied MUST implement the Bakame\Specification\Specification interface.

This interface only contains one method isSatisfiedBy(mixed $subject): bool. The method should not throw but if it does no mechanism MUST stop the exception from propagating outside the method.

Here's a quick example to illustrate the package usage.

First, we create a specification implementing class.

<?php

use Bakame\Specification\Specification;

final class OverDueSpecification implements Specification
{
    public function __construct(
        private DateTimeImmutable $date = new DateTimeImmutable('NOW', new DateTimeZone('UTC'))
    ) {
    }

    public function isSatisfiedBy(mixed $subject) : bool
    {
        return $subject instanceof Invoice
            && $subject->getDueDate() < $this->date;
    }
}

Then using the Bakame\Specification\Chain class and all the specifications created, we apply all the specifications according to the business rules.

Here's how the wikipedia example is adapted using the library.

<?php

use Bakame\Specification\Chain;

$overDue = new OverDueSpecification();
$noticeSent = new NoticeSentSpecification();
$inCollection = new InCollectionSpecification();

$sendToCollection = Chain::one($overDue)
    ->and($noticeSent)
    ->andNot($inCollection);

foreach ($service->getInvoices() as $invoice) {
    if ($sendToCollection->isSatisfiedBy($invoice)) {
        $invoice->sendToCollection();
    }
}

The Bakame\Specification\Chain class exposes the following logical chaining methods

Logical methods	isSatisfiedBy will return true
Chain::and	if the resulting the current specification and the those added are all satisfied
Chain::or	if at least one of the specifications is satisfied
Chain::andNot	if the current specification is satisfied AND the ones added are not
Chain::orNot	if the current specification is satisfied OR the ones added are not
Chain::not	will return the opposite of the current specification

To initiate a new specification logic chain the class exposes 4 named constructors

Named constructor	returned instance
Chain::one	new instance with a specification attach to it
Chain::all	with all specifications attach to it like Chain::and
Chain::any	with all specifications attach to it like Chain::or
Chain::none	with all specifications attach to it like Chain::not

All the methods from the Bakame\Specification\Chain accept variadic Bakame\Specification\Specification implemented classes except for the Chain::not method which takes not parameter at all.

Creating more complex rules that you can individually test becomes trivial as do their maintenance.

Tips on how to validate a list of subject.

Array

To filter an array of subjects you can use the array_filter function

<?php
$invoiceCollection = array_filter(
    fn (Invoice $invoice): bool => $sendToCollection->isSatisfiedBy($invoice),
    $respository->getInvoices()
);

foreach ($invoiceCollection as $invoice) {
    $invoice->sendToCollection();
}

Traversable

To filter a traversable structure or a generic iterator you can use the CallbackFilterIterator class.

<?php
$invoiceCollection = new CallbackFilterIterator(
    $respository->getInvoices(),
    fn (Invoice $invoice): bool => $sendToCollection->isSatisfiedBy($invoice),
);

foreach ($invoiceCollection as $invoice) {
    $invoice->sendToCollection();
}

Collections

The package can be used directly on collection that supports the filter method like Doctrine collection classes.

<?php
$invoiceCollection = $respository->getInvoices()->filter(
    fn (Invoice $invoice): bool => $sendToCollection->isSatisfiedBy($invoice)
);

foreach ($invoiceCollection as $invoice) {
    $invoice->sendToCollection();
}

Collection Macro

An alternative for Laravel collections is to register a macro:

<?php

declare(strict_types=1);

use Bakame\Specification\Specification;
use Illuminate\Support\Collection;

Collection::macro('satisfies', fn (Specification $specification): Collection =>
    $this->filter(
        fn ($item): bool => $specification->isSatisfiedBy($item);
    )
);

And then be used as described below:

$invoiceCollection = $invoices->all()->satifies($sendToCollection);
foreach ($invoiceCollection as $invoice) {
    $invoice->sendToCollection();
}

Contributing

Contributions are welcome and will be fully credited. Please see CONTRIBUTING and CODE OF CONDUCT for details.

Testing

The library:

• has a PHPSpec test suite
• has a coding style compliance test suite using PHP CS Fixer.
• has a code analysis compliance test suite using PHPStan and Psalm.

To run the tests, run the following command from the project folder.

$ composer test

Security

If you discover any security related issues, please email [email protected] instead of using the issue tracker.

Credits

• ignace nyamagana butera
• All Contributors

Attribution

The package is a fork of the work of greydnls on greydnls/spec.

License

The MIT License (MIT). Please see License File for more information.