Example of an ValidationParser for changing parameter keys to snake case

SnakeCaseValidationParser.php

<?php

namespace Smoost\UtilityBundle\Parser;

use Nelmio\ApiDocBundle\DataTypes;
use Nelmio\ApiDocBundle\Parser\ValidationParser;

class SnakeCaseValidationParser extends ValidationParser
{
    /**
     * Recursively parse constraints.
     *
     * @param  $className
     * @param  array $visited
     * @return array
     */
    protected function doParse($className, array $visited, $groups = [])
    {
        $params = array();
        $classdata = $this->factory->getMetadataFor($className);
        $properties = $classdata->getConstrainedProperties();

        $refl = $classdata->getReflectionClass();
        $defaults = $refl->getDefaultProperties();

        foreach ($properties as $property) {
            $vparams = array();

            $vparams['default'] = isset($defaults[$property]) ? $defaults[$property] : null;

            $pds = $classdata->getPropertyMetadata($property);
            foreach ($pds as $propdata) {
                
                 // apply exclusion strategies
                if ( TRUE === $this->shouldSkipProperty( $propdata, $groups ) ){
                    continue 2;
                }
                
                $constraints = $propdata->getConstraints();

                foreach ($constraints as $constraint) {
                    $vparams = $this->parseConstraint($constraint, $vparams, $className, $visited);
                }
            }

            if (isset($vparams['format'])) {
                $vparams['format'] = join(', ', $vparams['format']);
            }

            foreach (array('dataType', 'readonly', 'required', 'subType') as $reqprop) {
                if (!isset($vparams[$reqprop])) {
                    $vparams[$reqprop] = null;
                }
            }

            // check for nested classes with All constraint
            if (isset($vparams['class']) && !in_array($vparams['class'], $visited) && null !== $this->factory->getMetadataFor($vparams['class'])) {
                $visited[] = $vparams['class'];
                $vparams['children'] = $this->doParse($vparams['class'], $visited);
            }

            $vparams['actualType'] = isset($vparams['actualType']) ? $vparams['actualType'] : DataTypes::STRING;
            $property = ltrim(strtolower(preg_replace('/[A-Z]/', '_$0', $property)));
            $params[$property] = $vparams;
        }

        return $params;
    }
    
    
    protected function shouldSkipProperty( PropertyMetadata $propdata, $groups = array() ){
        return count(array_intersect($groups, array_keys($propdata->constraintsByGroup)))  == 0;
    }


}

This is not working for recent versions of nelmioapidocbundle