doctrine:
    dbal:
        driver:   %database_driver%
        host:     %database_host%
        dbname:   %database_name%
        user:     %database_user%
        password: %database_password%

    orm:
        auto_generate_proxy_classes: %kernel.debug%
        entity_managers:
            default:
                auto_mapping: true
                dql:
                    datetime_functions:
                        YEAR: Acme\DemoBundle\DQL\Year

<?php

use Doctrine\ORM\Query\AST\Functions\FunctionNode;

/**
 * DateDiffFunction ::= "YEAR" "(" ArithmeticPrimary ")"
 */
class Year extends FunctionNode
{
    public $dateExpression = null;

    public function parse(\Doctrine\ORM\Query\Parser $parser)
    {
        $parser->match(Lexer::T_IDENTIFIER);
        $parser->match(Lexer::T_OPEN_PARENTHESIS);
        $this->dateExpression = $parser->ArithmeticPrimary();
        $parser->match(Lexer::T_CLOSE_PARENTHESIS);
    }

    public function getSql(\Doctrine\ORM\Query\SqlWalker $sqlWalker)
    {
        return 'YEAR(' . $this->dateExpression->dispatch($sqlWalker) . ')';
    }
}