在 Doctrine2 中发出查询之前是否可以检查关联是否存在？例子：
/**
* @ORM\Entity
*/
class Product
{
/**
* @ORM\OneToMany(targetEntity="Feature", inversedBy="product")
*/
public $features;
}
我想检查（实际上没有发出查询本身）关联是否product.features存在。
编辑：出于好奇，我正在编写一个服务（真的是一个助手）来做一些基于 GET 参数的集合过滤：
public function initialize($entityName, $key)
{
// Defaults are empty values and empty collection
$this->values = array();
$this->collection = new ArrayCollection();
// If "$key" GET parameter is null or blank return this instance
if(is_null($value = $this->request->get($key))
|| strlen(trim($value)) == 0) return $this;
// Split the parameter value based on separator (typically a comma)
$re = '/\s*' . $this->separator . '\s*/';
// Return this instance if no values are found
if(!($set = preg_split($re, $value, 0, PREG_SPLIT_NO_EMPTY))) return $this;
// Guess the repository fully qualified name and entity name
$guesser = $this->getManagementGuesser();
$repoName = $guesser->guessRepositoryName();
$entityName = $guesser->guessEntityName();
// Get the repository for the entity and create the builder
$qb = $this->getRepository($repoName)->createQueryBuilder('e');
// Check if a relation named $key exists and throw a LogicException
$exists = $this->getEntitiesUtility()->checkRelation($entityName, $key);
if(!$exists) throw new \LogicException("Relation named '$key' not found.");
// Other stuff
}
相关的部分是：
$this->getEntitiesUtility()->checkRelation($entityName, $relationName);