<?php

namespace Foo\SomeBundle\Repository;
use Foo\SomeBundle\Dependency;
use Doctrine\ORM\EntityRepository;

class SomeRepository extends EntityRepository implements SomeContract
{
    /**
     * @var Dependency
     */
    private $dependency;

    public function setDependency(Dependency $dependency)
    {
        $this->dependency = $dependency;
    }

    public function findSomething(Directory $directory)
    {
        $dependency = $this->getDependency();
        // Your DQL.
    }

    private function getDependency()
    {
        if (!$this->dependency instanceof Dependency) {
            throw \LogicException('Missing Dependency');
        }

        return $this->dependency;
    }
}