Ok, I have a User entity as follows <?php class User { /** * @var integer * @Id * @Column(type="integer") * @GeneratedValue */ protected $id; /** * @var \Application\Entity\Url[] * @OneToMany(targetEntity="Url", mappedBy="user", cascade={"persist", "remove"}) */ protected $urls; public function __construct() { $this->urls = new \Doctrine\Common\Collections\ArrayCollection(); } public function addUrl($url) { // This is where I have a problem } } Now, what I want to do is check if the User has already the $url in the $urls ArrayCollection before persisting the $url. Now some of the examples I found says we should do something like if (!$this->getUrls()->contains($url)) { // add url } but this doesn't work as this compares the element values. As the $url doesn't have id value yet, this will always fail and $url will be dublicated. So I'd really appreciate if someone could explain how I can add an element to the ArrayCollection without persisting it and avoiding the duplication? Edit I have managed to achive this via $p = function ($key, $element) use ($url) { if ($element->getUrlHash() == $url->getUrlHash()) { return true; } else { return false; } }; But doesn't this still load all urls and then performs the check? I don't think this is efficient as there might be thousands of urls per user.