Simple example of a transformer class

Person Transformer

<?php
namespace Infrastructure\Database;

use DateTime,
    Domain\Person\PersonEntity as Person,
    Domain\Person\Name,
    Domain\Person\Email;

class ExamplePersonDomainObjectTransformer extends AbstractTransformer
{
    public function transform(array $data)
    {
        $name = new Name($data['first'], $data['last'], $data['suffix']);
        $email = new Email($data['email_address']);
        $person = new Person($name, $email, new DateTime($timestamp));
        return $person;
    }
}

Precinct Transformer

<?php
namespace Acme\Precincts\Transformers;

use Acme\Support\Transformers\AbstractTransformer;

class PrecinctApiTransformer extends AbstractTransformer
{
    /**
     * Fields that should be converted into individual district objects
     * @var array
     */
    protected $districtFields = array(
        'congressional'     => 'US House',
        'tn_senate'         => 'TN Senate',
        'tn_house'          => 'TN House',
        'judicial'          => 'Judicial',
        'city'              => 'Municipal',
        'school'            => 'School',
        'ward'              => 'Ward',
        'special_school'    => 'Special School'
    );

    /**
     * @param \Acme\Precincts\Precinct $precinct
     * @return array
     */
    public function transform($precinct)
    {
        //TODO: Add tests
        $transformed = array();
        foreach($this->districtFields as $attribute => $label) {
            if($precinct->$attribute) {
                $transformed[] = array(
                    'name'  => $label,
                    'value' => (string) $precinct->$attribute
                );
            }
        }
        return $transformed;
    }

}

Transformer Class Example

<?php
namespace Acme\Support\Transformers;

abstract class AbstractTransformer implements Transformer
{

    /**
     * Transforms a single item
     * @param mixed $item The item to transform
     * @return mixed $item The transformed item
     */
    public abstract function transform($item);

    public function transformCollection($collection)
    {
        $transformed = array();
        foreach($collection as $item) {
            $transformed[] = $this->transform($item);
        }
        return $transformed;
    }

    /**
     * Iterates through an array and converts all null fields to empty strings
     * @param array $values
     * @return array
     */
    protected function convertNullToEmptyString(array $values)
    {
        foreach($values as $key => $value) {
            if($values[$key] === null) {
                $values[$key] = '';
            }
        }
        return $values;
    }

    /**
     * Converts a generic US numeric phone number into a properly-formatted one
     * Assumes extensions are formatted (primary phone number)x####
     * @param string $phone The original phone number
     */
    protected function transformPhoneNumber($phone)
    {
        $phone = preg_replace('@[^\dx]@', '', $phone);
        if(0 == (int) $phone || 'NULL' == $phone) {
            $converted = null;
        } else {
            $converted = array();
            $converted[] = '(';
            $converted[] = substr($phone, 0, 3);
            $converted[] = ') ';
            $converted[] = substr($phone, 3, 3);
            $converted[] = '-';
            $converted[] = substr($phone, 6);
            $converted = implode('', $converted);
        }
        return $converted;
    }

}