Symfony – How to add an unbound field to a form in Symfony which is otherwise bound to an entity

You are approaching it wrong, you need to let the database do the matching, not get all rows and do the matching in php.

Something like:

$sql = "SELECT bookingref FROM starpick WHERE obsolete = 0 AND bookingref='" . mysql_real_escape_string($_POST["code"]) . "'";    // better use a prepared statement by the way but you'll have to check the manual for mysqli

and then just check if a row if found.

I'm using PDO myself, but here is manual on prepared statements for mysqli.

There is a fairly simple solution to this problem actually. I just needed a form type extension to extend the base form type to allow an extra available option: http://symfony.com/doc/2.3/cookbook/form/create_form_type_extension.html

Following through the example in the docs, I created a new form type extension:

// src/Acme/FrontendBundle/Form/Extension/FormTypeExtension.php

namespace Acme\FrontendBundle\Form\Extension;

use Symfony\Component\Form\AbstractTypeExtension;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\Form\FormView;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

/**
 * Class FormTypeExtension
 * @package Acme\FrontendBundle\Form\Extension
 */
class FormTypeExtension extends AbstractTypeExtension
{
    /**
     * Extends the form type which all other types extend
     *
     * @return string The name of the type being extended
     */
    public function getExtendedType()
    {
        return 'form';
    }

    /**
     * Add the extra row_attr option
     *
     * @param OptionsResolverInterface $resolver
     */
    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'row_attr' => array()
        ));
    }

    /**
     * Pass the set row_attr options to the view
     *
     * @param FormView $view
     * @param FormInterface $form
     * @param array $options
     */
    public function buildView(FormView $view, FormInterface $form, array $options)
    {
        $view->vars['row_attr'] = $options['row_attr'];
    }
}

Then I registered the service in my bundle...

<!-- Form row attributes form extension -->
<service id="acme.form_type_extension" class="Acme\FrontendBundle\Form\Extension\FormTypeExtension">
    <tag name="form.type_extension" alias="form" />
</service>

Since every widget extends the base form type this then allows me to pass this new row_attr option through on any field, eg:

$builder
    ->add('first_name', 'text', array(
        'row_attr' => array(
            'class' => 'form-row-split'
        )
    ));

Then the twig overrides to make use of the new row_attr option:

{% block form_row %}
    <div {{ block('form_row_attributes') }}>
        {{ form_label(form) }}
        {{ form_widget(form) }}
        {{ form_errors(form) }}
    </div>
{% endblock form_row %}

{% block form_row_attributes %}
    {% spaceless %}
        {% for attrname, attrvalue in row_attr %}{{ attrname }}="{{ attrvalue }}" {% endfor %}
    {% endspaceless %}
{% endblock form_row_attributes %}

And it's done!

(For completeness, my full twig override still merges in the form-row and error classes in like so:

{% set row_attr = row_attr|merge({'class': 'form-row' ~ (row_attr.class is defined ? ' ' ~ row_attr.class : '') ~ (errors|length > 0 ? ' error' : '')} ) %}

.. but thats not really necessary for answering my own question :P )