4.3. Entity-Attribute-Value (EAV)

The Entity–attribute–value (EAV) pattern in order to implement EAV model with PHP.

4.3.1. Purpose

The Entity–attribute–value (EAV) model is a data model to describe entitieswhere the number of attributes (properties, parameters) that can be usedto describe them is potentially vast, but the number that will actually applyto a given entity is relatively modest.

4.3.2. UML Diagram

4.3.3. Code

You can also find this code on GitHub

Entity.php

<?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

<?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

<?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);
    }
}

4.3.4. Test

Tests/EAVTest.php

<?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);
    }
}