Symfony Form — JsonType

Handling Json input

Use case

Imagine given use case of sending whole JSON via form (by encoding array on Frontend) like that:

Data sending & handling

Related article: Handling Vue.js form in Symfony

The issue

Symfony form handler allows using different input types like TextType, ArrayChoiceList, ChoiceType etc. while using Array based type the result is an empty array. The only one working case is TextType but it still yields just raw json — but that’s undesired result.

JsonType

After struggling for a while, the only working solution I’ve found is providing new input type (JsonType) and new DataTransformer like that:

DataTransformer

<?php

namespace App\Form\DataTransformer;

use Symfony\Component\Form\DataTransformerInterface;

/**
 * Handles transforming json to array and backward
 */
class JsonTransformer implements DataTransformerInterface
{

    /**
     * @inheritDoc
     */
    public function reverseTransform($value): mixed
    {
        if (empty($value)) {
            return [];
        }

        return json_decode($value);
    }

    /**
     * @ihneritdoc
     */
    public function transform($value): mixed
    {
        if (empty($value)) {
            return json_encode([]);
        }

        return json_encode($value);
    }
}

JsonType

<?php

namespace App\Form\Type;

use App\Form\DataTransformer\JsonTransformer;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Serializer\SerializerInterface;

/**
 * Handles json based input (for example multiselect tag)
 * Will only transform the json to array (and back),
 *
 * If necessary, could probably accept custom options (className) which would be used to
 * transform the data into given class via {@see SerializerInterface}
 */
class JsonType extends AbstractType
{
    /**
     * @inheritDoc
     */
    public function getParent(): string
    {
        return TextType::class;
    }

    /**
     * @inheritDoc
     */
    public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $builder->addModelTransformer(new JsonTransformer());
    }
}

Summary

The end result is an array transformed from the json.