4.4. Encja-Atrybut-Wartość (Entity-Attribute-Value (EAV))

Wzorzec Encja-Atrybut-Wartość pozwala zaimplementować model EAV w PHP.

4.4.1. Przeznaczenie

Model Encja-Atrybut-Wartość (EAW, ang. Entity-Attribute-Value - EAV) jest modelem danych, który upraszcza opisywanie encji posiadających potencjalnie wiele atrybutów (właściwości, parametrów), kiedy nie wszystkie z nich są na raz używane.

4.4.2. Diagram UML

EAV UML Diagram

4.4.3. Code

Ten kod znajdziesz również na GitHub.

Entity.php

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<?php

namespace DesignPatterns\More\EAV;

class Entity
{
    /**
     * @var \SplObjectStorage
     */
    private $values;

    /**
     * @var string
     */
    private $name;

    /**
     * @param string $name
     * @param Value[] $values
     */
    public function __construct(string $name, $values)
    {
        $this->values = new \SplObjectStorage();
        $this->name = $name;

        foreach ($values as $value) {
            $this->values->attach($value);
        }
    }

    public function __toString(): string
    {
        $text = [$this->name];

        foreach ($this->values as $value) {
            $text[] = (string) $value;
        }

        return join(', ', $text);
    }
}

Attribute.php

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<?php

namespace DesignPatterns\More\EAV;

class Attribute
{
    /**
     * @var \SplObjectStorage
     */
    private $values;

    /**
     * @var string
     */
    private $name;

    public function __construct(string $name)
    {
        $this->values = new \SplObjectStorage();
        $this->name = $name;
    }

    public function addValue(Value $value)
    {
        $this->values->attach($value);
    }

    /**
     * @return \SplObjectStorage
     */
    public function getValues(): \SplObjectStorage
    {
        return $this->values;
    }

    public function __toString(): string
    {
        return $this->name;
    }
}

Value.php

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<?php

namespace DesignPatterns\More\EAV;

class Value
{
    /**
     * @var Attribute
     */
    private $attribute;

    /**
     * @var string
     */
    private $name;

    public function __construct(Attribute $attribute, string $name)
    {
        $this->name = $name;
        $this->attribute = $attribute;

        $attribute->addValue($this);
    }

    public function __toString(): string
    {
        return sprintf('%s: %s', $this->attribute, $this->name);
    }
}

4.4.4. Testy

Tests/EAVTest.php

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<?php

namespace DesignPatterns\More\EAV\Tests;

use DesignPatterns\More\EAV\Attribute;
use DesignPatterns\More\EAV\Entity;
use DesignPatterns\More\EAV\Value;
use PHPUnit\Framework\TestCase;

class EAVTest extends TestCase
{
    public function testCanAddAttributeToEntity()
    {
        $colorAttribute = new Attribute('color');
        $colorSilver = new Value($colorAttribute, 'silver');
        $colorBlack = new Value($colorAttribute, 'black');

        $memoryAttribute = new Attribute('memory');
        $memory8Gb = new Value($memoryAttribute, '8GB');

        $entity = new Entity('MacBook Pro', [$colorSilver, $colorBlack, $memory8Gb]);

        $this->assertEquals('MacBook Pro, color: silver, color: black, memory: 8GB', (string) $entity);
    }
}