Extract, from a ConstraintViolationsList object, an associative array where the keys are property names and values are error messages. This function was originally created to be used inside a Propel2 project. Anyway, it can be used in every project following the PSR-0 and using the Symfony Validator Component.

violations_to_array.php

<?php
/**
 * This function was originally created to be used inside a Propel2 project.
 * Anyway, it can be used in every project following the PSR-0 and using the Symfony Validator Component.
 *
 * @see http://symfony.com/doc/current/book/validation.html
 * @see https://github.com/propelorm/Propel2/blob/master/documentation/behaviors/validate.markdown
 */

use Symfony\Component\Validator\ConstraintViolationList;

/**
 * Extract, from a ConstraintViolationList object, an associative array as follow:
 * <code>
 *     array(
 *         'property1.1' => array('message1.1', 'message1.2'),
 *         'property1.2' => array('message2')
 *         ........
 *     )
 * </code>
 * with the possibility to filter a given property path.
 *
 * @param $violationsList ConstraintViolationList object
 * @param string $propertyPath The name of the property to filter
 *
 * @return array
 */
function violations_to_array(ConstraintViolationList $violationsList, $propertyPath = null)
{
    $output = array();

    foreach ($violationsList as $violation) {
        $output[$violation->getPropertyPath()][] = $violation->getMessage();
    }

    if (null !== $propertyPath) {
        if (array_key_exists($propertyPath, $output)) {
            $output = array_intersect_key($output, array($propertyPath => 0));
        } else {
            return array();
        }
    }

    return $output;
}

violationsToArrayFunctionTest.php

<?php

require 'violations_to_array.php';

use Symfony\Component\Validator\ConstraintViolation;
use Symfony\Component\Validator\ConstraintViolationList;

class ConstraintViolationListTest extends \PHPUnit_Framework_TestCase
{
    protected $list;

    protected function setUp()
    {
        $this->list = new ConstraintViolationList();
    }

    protected function tearDown()
    {
        $this->list = null;
    }

    public function testToArray()
    {
        $this->list = new ConstraintViolationList(array(
            $this->getViolation('Error 1', 'Root', 'foo'),
            $this->getViolation('Error 2', 'Root', 'foo'),
            $this->getViolation('Error 3', 'Root', 'bar'),
            $this->getViolation('Error 4', 'Root 2', 'foo'),
            $this->getViolation('Error 5', 'Root 3', 'baz'),
        ));

        $expectedNoFilters = array(
            'foo' => array('Error 1', 'Error 2', 'Error 4'),
            'bar' => array('Error 3'),
            'baz' => array('Error 5')
        );
        $this->assertEquals($expectedNoFilters, violations_to_array($this->list));

        $expectedFilterPropertyPath = array(
            'foo' => array('Error 1', 'Error 2', 'Error 4')
        );
        $this->assertEquals($expectedFilterPropertyPath, violations_to_array($this->list, 'foo'));

        //Wrong value causes to return empty array
        $this->assertEquals(array(), violations_to_array($this->list, 'wrong'));
    }

    protected function getViolation($message, $root = null, $propertyPath = null)
    {
        return new ConstraintViolation($message, $message, array(), $root, $propertyPath, null);
    }
}