Decoding JSON in Twig

Question

Is is possible to decode JSON in twig? Googling doesn't seem to yield anything about this. Does decoding JSON in Twig not make sense?

---

I'm trying to access 2 entity properties on an Symfony2's entity field type (Entity Field Type).

After coming across 2 previous SO questions ( Symfony2 entity field type alternatives to "property" or "__toString()"? and Symfony 2 Create a entity form field with 2 properties ) which suggested adding an extra method to an entity to retrieve a customized string rather than an entity attribute, I thought of (and did) returning a JSON string representing an object instance.

Somewhere in the entity class:

/**
 * Return a JSON string representing this class.
 */
public function getJson()
{
   return json_encode(get_object_vars($this));
}

And in the form (something like):

$builder->add('categories', 'entity', array (
...
'property' => 'json',
...
));

Afterwards, I was hoping to json_decode it in Twig...

{% for category in form.categories %}
    {# json_decode() part is imaginary #}
    {% set obj = category.vars.label|json_decode() %}
{% endfor %}

Answer 1

That's easy if you extend twig.

First, create a class that will contain the extension:

<?php
 
namespace Acme\DemoBundle\Twig\Extension;

use Symfony\Component\DependencyInjection\ContainerInterface;  
use \Twig_Extension;

class VarsExtension extends Twig_Extension
{
    protected $container;
 
    public function __construct(ContainerInterface $container) 
    {
        $this->container = $container;
    }
      
    public function getName() 
    {
        return 'some.extension';
    }
    
    public function getFilters() {
        return array(
            'json_decode'   => new \Twig_Filter_Method($this, 'jsonDecode'),
        );
    }

    public function jsonDecode($str) {
        return json_decode($str);
    }
}

Then, register that class in your Services.xml file:

<service id="some_id" class="Acme\DemoBundle\Twig\Extension\VarsExtension">
        <tag name="twig.extension" />
        <argument type="service" id="service_container" />
</service>

Then, use it on your twig templates:

{% set obj = form_label(category) | json_decode %}

Answer 2

I came up with a way of getting to my JSON and I thought I'd share it here in case its usefult to someone else.

so in my case I have maybe 10 records (layouts) returned from a mysql db and each row has a field called properties which is a json string. So, I can easily pull out the records and send them to the template like so:

echo $twig->render('template.html.twig', array(
      "layouts" => $layouts,
));

So far so good, However when I do my {% for layout in layouts %} in twig there is no way to get to the properties field items as they are still a json string.

So just before I passed $layouts to the twig template I did the following:

foreach($layouts as $i => $v)
{
      $layouts[$i]->decoded = json_decode($v->getProperties());
}

by doing this Ive created a variable on the fly within my object called 'decoded' which contains the json decoded object.

So now in my template I can access my json items by {{ layout.decoded.whatever }}

This might be a bit hacky and not to everyones idea of a good solution. I works well for me, very little overhead and means I dont have to mess about with extending twig as Im doing the work before it gets to the template.

Answer 3

An alternative to all above.
And I don't know whether this is the optimal solution, but it works.

1) Create a helper function and register that function it.

<?php
function twig_json_decode($json)
{
    return json_decode($json, true);
}

2) Use this function in your twig file.

{% set res = twig_json_decode(json) %}
# above will return an array which can be iterated

{% for r is res %}
    {{ r }}
{% endfor %}