使用SQL中的RAND（）函数与Doctrine2

我已经被困住了大约10个小时

I've been stuck with this for about 10 hours

我需要使用这个查询（ORDER BY RAND的优化版本）

I need to use this query (an optimized version of ORDER BY RAND)

public function findAllRandom()
{
   return $this->getEntityManager()
    ->createQuery(
        'SELECT p FROM GabrielUploadBundle:Image p WHERE RAND() < 0.0001 ORDER BY RAND() LIMIT 20')
    ->getResult();
}

当然，由于我使用DQL，我需要实现RAND ）函数

And of course since I'm using DQL I need to implement the RAND() function

<?php
namespace Gabriel\UploadBundle\DoctrineFunctions;
use Doctrine\ORM\Query\Lexer;

/**
 * RandFunction ::= "RAND" "(" ")"
 */
class Rand extends \Doctrine\ORM\Query\AST\Functions\FunctionNode
{ 
    public function parse(\Doctrine\ORM\Query\Parser $parser)
    {
        $parser->match(Lexer::T_IDENTIFIER);
        $parser->match(Lexer::T_OPEN_PARENTHESIS);
        $parser->match(Lexer::T_CLOSE_PARENTHESIS);
    }

    public function getSql(\Doctrine\ORM\Query\SqlWalker $sqlWalker)
    {
        return 'RAND()';
    }
}

// Config.yml

//Config.yml

orm:
(...)
    dql:
       numeric_functions:
         Rand: Gabriel\UploadBundle\DoctrineFunctions\Rand

问题是我不断得到这个错误：

The problem is I keep getting this error:

[Syntax Error] line 0, col 77: Error: Expected end of string, got '('

RAND（）源代码的来源：

The source of the RAND() source code:

https://gist.github.com/Ocramius/919465

如何从配置中添加：

http://symfony.com/doc/current/cookbook/doctrine/custom_dql_functions.html

演示关于向DQL添加功能

demo about adding functions to DQL

http://punkave.com/window/2012/07/24/for-the-php-crowd-adding-custom-functions-to-doctrine-2-dql

编辑：
经过进一步的研究，我发现dql中不支持按函数排序：
source ：
http://docs.doctrine-project.org/en/2.1/reference/faq.html#can-i-sort-by-a-function-for- example-order-by-rand-in-dql

要解决此问题，可以添加HIDDEN值

To work around this the HIDDEN value can be added

public function findAllRandom()
{
   return $this->getEntityManager()
    ->createQuery(
        'SELECT p,RAND() AS HIDDEN rand FROM GabrielUploadBundle:Image p ORDER BY rand')
    ->getResult();
}

但由于某些原因，它不适用于WHERE子句

but for some reason it doesn't work with the WHERE clause

public function findAllRandom()
{
   return $this->getEntityManager()
    ->createQuery(
        'SELECT p,RAND() AS HIDDEN rand FROM GabrielUploadBundle:Image p WHERE rand < 0.00001 ORDER BY rand')
    ->getResult();
}

对于where子句的解决方案将不胜感激，每个人都知道使用ORDER BY RAND（）函数可能会减慢服务器（在我们的情况下甚至崩溃）

A solution for the where clause would be appreciated, everyone knows that using the ORDER BY RAND() function can slow down the server (in our case even crash it)