MultiOrderTransformer.php

<?php

namespace LeftDevel\Form\Transformer;

use Symfony\Component\Form\DataTransformerInterface;
use Symfony\Component\Form\Exception\TransformationFailedException;

class MultiOrderTransformer implements DataTransformerInterface
{
    public function transform($length)
    {
        if (!$length) {
            return [
                'feet' => 0,
                'inches' => 0,
            ];
        }
        
        return [
            'feet' => intval($length / 12),
            'inches' => $length % 12,
        ];
    }

    public function reverseTransform($parts)
    {
        if (!is_array($parts)) {
            throw new TransformationFailedException('Expected array');
        }

        if (!(isset($parts['feet']) && isset($parts['inches']))) {
            throw new TransformationFailedException('Feet and Inches must be defined');
        }

        return $parts['feet'] * 12 + $parts['inches'];
    }
}

MultiOrderType.php

<?php

namespace LeftDevel\Form\Type;

use Symfony\Component\OptionsResolver\OptionsResolverInterface,
    Symfony\Component\Form\AbstractType,
    Symfony\Component\Form\FormBuilderInterface;

use LeftDevel\Form\Transformer\MultiOrderTransformer;

class MultiOrderType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->addViewTransformer(new MultiOrderTransformer())
            ->add('feet', 'text')
            ->add('inches', 'text')
        ;
    }

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array('compound' => true));
    }

    public function getName()
    {
        return 'multi_order_type';
    }
}