$new = new InterviewReview();

$question = new InterviewReviewQuestion();
$new->addQuestion($question);

$em->persist($new);
$em->flush();

An exception occurred while executing 'INSERT INTO interview_review_question (question, tags, created_at, interview_review_id) VALUES (?, ?, ?, ?)' with params {"1":"asdfg","2":"asdfg","3":null,"4":null}:

Column 'interview_review_id' cannot be null

/**
 * InterviewReview
 *
 * @ORM\Table(name="interview_review")
 * @ORM\Entity
 */
class InterviewReview
{
    /**
     * @var integer
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @var Doctrine\Common\Collections\ArrayCollection
     *
     * @ORM\OneToMany(targetEntity="Absolvent\AbsolventBundle\Entity\InterviewReviewQuestion", cascade={"persist", "remove"}, mappedBy="interview_review")
     * @ORM\JoinColumn(name="interview_review", referencedColumnName="id")
     */
    private $questions;

    /**
     * Add question
     *
     * @param \Absolvent\AbsolventBundle\Entity\InterviewReviewQuestion $question
     * @return InterviewReview
     */
    public function addQuestion(\Absolvent\AbsolventBundle\Entity\InterviewReviewQuestion $question)
    {
        $this->questions[] = $question;

        return $this;
    }

    /**
     * Remove question
     *
     * @param \Absolvent\AbsolventBundle\Entity\InterviewReviewQuestion $question
     */
    public function removeQuestion(\Absolvent\AbsolventBundle\Entity\InterviewReviewQuestion $question)
    {
        $this->questions->removeElement($question);
    }

    /**
     * Get questions
     *
     * @return \Doctrine\Common\Collections\Collection
     */
    public function getQuestions()
    {
        return $this->questions;
    }
}


/**
 * InterviewReviewQuestion
 *
 * @ORM\Table(name="interview_review_question")
 * @ORM\Entity
 */
class InterviewReviewQuestion
{
    /**
     * @var integer
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @var Absolvent\AbsolventBundle\Entity\InterviewReview
     *
     * @ORM\ManyToOne(targetEntity="Absolvent\AbsolventBundle\Entity\InterviewReview", cascade={"persist", "remove"}, inversedBy="questions")
     * @ORM\JoinColumn(name="interview_review_id", referencedColumnName="id", nullable=false)
     */
    private $interview_review;

    /**
     * Get id
     *
     * @return integer
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Set interview_review
     *
     * @param \Absolvent\AbsolventBundle\Entity\InterviewReview $interviewReview
     * @return InterviewReviewQuestion
     */
    public function setInterviewReview(\Absolvent\AbsolventBundle\Entity\InterviewReview $interviewReview = null)
    {
        $this->interview_review = $interviewReview;

        return $this;
    }

    /**
     * Get interview_review
     *
     * @return \Absolvent\AbsolventBundle\Entity\InterviewReview
     */
    public function getInterviewReview()
    {
        return $this->interview_review;
    }
}