post.php

<?php

/**
 * @ORM\Entity
 */
class Post 
{
    ...

    /**
     * @ORM\OneToMany(targetEntity="App\Entity\Comment", mappedBy="post", orphanRemoval=true)
     */
    private $comments;

    /**
     * @ORM\OneToMany(targetEntity="App\Entity\History\HistoryRecord", mappedBy="post", orphanRemoval=true)
     */
    private $historyRecords;