Doctrine inserting error - File categories.php

<?php
namespace models;

/**
 * @Entity
 * @Table(name="categories")
 */
class Categories {
    /**
     * @Id
     * @Column(name="id", type="integer", nullable=false)
     * @GeneratedValue(strategy="AUTO")
     */
    protected $id;

    /**
     * @ManyToOne(targetEntity="Languages")
     */
    protected $languages;

    /**
     * @Column(type="integer", nullable=false)
     */
    protected $parent_id;

    /**
     * @Column(type="string", length="255", nullable=false)
     */
    protected $title;


    /* Setters & Getters */
    public function getId(){ return $this->id; }

    public function setLanguage($id){ $this->languages = (int)$id; }
    public function getLanguage(){ return $this->languages; }

    public function setParentId($parent){ $this->parent_id = $parent; }
    public function getParentId(){ return $this->parent_id; }

    public function setTitle($title){ $this->title = $title; }
    public function getTitle(){ return $this->title; }
}