doctrine2 DQL subquery 1 row limit - doctrine-orm

Question

I want to do a DQL query like:
$dql = "select p
from AcmeDemoBundle:UserTypeA p
where p.UserTypeB = :id
and (
select top 1 r.boolean
from AcmeDemoBundle:Registry r
)
= true";
But it seems that TOP 1 it's not a valid function in doctrine2.
I can't figure out how can I limit the result of the subquery to one row.

Answer 1

DQL does not support limits on subqueries and neither LIMIT nor OFFSET.
See http://www.doctrine-project.org/jira/browse/DDC-885

Answer 2

Although Doctrine doesn't natively support this, you could implement a custom function named FIRST() to achieve this:
<?php
use Doctrine\ORM\Query\AST\Functions\FunctionNode;
use Doctrine\ORM\Query\AST\Subselect;
use Doctrine\ORM\Query\Lexer;
use Doctrine\ORM\Query\Parser;
use Doctrine\ORM\Query\SqlWalker;
/**
* FirstFunction ::=
* "FIRST" "(" Subselect ")"
*/
class FirstFunction extends FunctionNode
{
/**
* #var Subselect
*/
private $subselect;
/**
* {#inheritdoc}
*/
public function parse(Parser $parser)
{
$parser->match(Lexer::T_IDENTIFIER);
$parser->match(Lexer::T_OPEN_PARENTHESIS);
$this->subselect = $parser->Subselect();
$parser->match(Lexer::T_CLOSE_PARENTHESIS);
}
/**
* {#inheritdoc}
*/
public function getSql(SqlWalker $sqlWalker)
{
return '(' . $this->subselect->dispatch($sqlWalker) . ' LIMIT 1)';
}
}
(More details: https://www.colinodell.com/blog/201703/limiting-subqueries-doctrine-2-dql)
You should really only use this for read-only purposes since Doctrine will not include other related entities in the result (which may become orphaned or lost if you save it).