Symfony Form choices customize the get url - forms

Question

So I have a search bar form that I need to temporarly wire up to a legacy non-symfony page.
the current get url looks like the following (url-decoded)
http://localhost:9090/lagacy_page?query=test&platforms[]=Mac,Windows
but I need to make the url look like the following
http://localhost:9090/lagacy_page?query=test&platforms=Mac,Windows
Symfony is making platforms an array, does anyone no if there is a way to force it to be a comma delimitated list?
Here is the buildForm method
/**
* method to build search bar form
*
* #param \Symfony\Component\Form\FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options)
{
// the platform selector
$builder->add('platform', 'choice',
['choices' => [
Platforms::ALL => 'All Software', // TODO: need to translate this
Platforms::WINDOWS => 'Windows',
Platforms::MAC => 'Mac',
Platforms::IOS => 'iOS',
Platforms::ANDROID => 'Android',
],
'multiple' => true,
'expanded' => true]);
// the actual search bar
$builder->add('query', 'search');
}

Answer 1

You will want to override how Symfony2 renders the choice field.
The documentation has plenty of information about how to customize Form rendering.
If only the choice type of search form needs this, you will need to create a custom type in order to avoid conflicts with the other forms of your website.
In short, if you override the choice type using the first doc and you do not use a custom type every choice type will use the same behavior (the one you will create for your search form) and you probably don't want that.
An easy alternative solution would be to apply a custom form_div_layout.html.twig file directly to the form object. There wouldn't be any conflicts with other forms as you would use a custom template just for the search form.
After reading the docs my answer will make more sense and you will be able to solve your problem.

Answer 2

You have to use two form elements, since Symfony doing it in right way (according to HTML specifcation)
/**
* method to build search bar form
*
* #param \Symfony\Component\Form\FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options)
{
// the platform selector
$builder->add('platform_choice', 'choice',
['choices' => [
Platforms::ALL => 'All Software', // TODO: need to translate this
Platforms::WINDOWS => 'Windows',
Platforms::MAC => 'Mac',
Platforms::IOS => 'iOS',
Platforms::ANDROID => 'Android',
],
'multiple' => true,
'expanded' => true,
'attr' => [
'class' => 'platform-sorce'
])
->add('platform', 'hidden', [
'attr' => [
'class' => 'real-platform'
]
]);
// the actual search bar
$builder->add('query', 'search');
}
Then add JS updating you hidden field, since 'platform_choice' is disabled and wont be send.
$(function(){
var $real_platform = $('.real-platform'),
$platform_source = $('.platform-source');
$platform_source.change(function(){
$real_platform.val($(this).val().join(',');
});
$('#your-form").submit(function(){
$platform_source.attr('disabled', true);
return true;
});
});