<?php

namespace AppBundleDocument;

use DoctrineBundleMongoDBBundleValidatorConstraintsUnique as MongoDBUnique;
use DoctrineODMMongoDBMappingAnnotations as MongoDB;
use SymfonyComponentValidatorConstraints as Assert;

/**
 * @MongoDBDocument(collection="users")
 * @MongoDBUnique(fields="{id, email}")
 */
class User
{
   // ...
   /**
     * @MongoDBField(type="collection")
     */
    protected $loginLast90Days;

    // ...

    /**
     * Set loginLast90Days
     *
     * @param collection $loginLast90Days
     * @return $this
     */
    public function setLoginLast90Days($loginLast90Days)
    {
        $this->loginLast90Days = $loginLast90Days;
        return $this;
    }

    /**
     * Get loginLast90Days
     *
     * @return collection $loginLast90Days
     */
    public function getLoginLast90Days()
    {
        return $this->loginLast90Days;
    }

    public function addLoginLast90Days($login)
    {
        $this->loginLast90Days[] = $login;
        return $this;
    }

    public function removeLoginLast90Days($login)
    {
        $this->loginLast90Days->removeElement($login);
        return $this;
    }

    // ...
}

$dm = $this->get('doctrine_mongodb');

            $user = $dm->getRepository('AppBundle:User')->findOneBy(array('gmail' => $email));

$user->addLoginLast90Days(time());

$dm = $this->get('doctrine_mongodb')->getManager();
$dm->persist($user);
$dm->flush();