Symfony3 Doctrine Single Table Inhertiance SQLSTATE[23000]: Integrity constraint violation - php

Question

I am new to Symfony and I am trying to do a simple Blog. I have users in my database as authors of Comments and 2 types of comments - PostComment and ReplyComment which both extend abstract class Comments. I am trying to save comment to the DB, but I am stuck with this error :
An exception occurred while executing 'INSERT INTO comment (text,
author_id, post_id, comment_type) VALUES (?, ?, ?, ?)' with params
["Lorem ipsum", 1, 1, "post_comment"]:
SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or
update a child row: a foreign key constraint fails
(blog_symfony.comment, CONSTRAINT FK_9474526CDB1174D2 FOREIGN
KEY (post_comment_id) REFERENCES comment (id))
This is abstract Comment Class :
use Doctrine\ORM\Mapping as ORM;
/**
* #ORM\Entity()
* #ORM\Table(name="comment")
* #ORM\InheritanceType("SINGLE_TABLE")
* #ORM\DiscriminatorColumn(name="comment_type", type="string")
* #ORM\DiscriminatorMap({"post_comment" = "PostComment", "reply_comment" = "ReplyComment"})
*/
abstract class Comment
{
/**
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
* #ORM\Column(type="integer")
*/
protected $id;
/**
* #ORM\ManyToOne(targetEntity="AppBundle\Entity\User", inversedBy="userComments")
*/
protected $author;
/**
* #ORM\Column(type="string")
*/
protected $text;
/**
* #return integer $id
*/
public function getId()
{
return $this->id;
}
/**
* #return string $author
*/
public function getAuthor()
{
return $this->author;
}
/**
* #param string $author
*/
public function setAuthor($author)
{
$this->author = $author;
}
/**
* #return string $text
*/
public function getText()
{
return $this->text;
}
/**
* #param string $text
*/
public function setText($text)
{
$this->text = $text;
}
}
This is a post comment class
use Doctrine\ORM\Mapping as ORM;
/**
* #ORM\Entity(repositoryClass="AppBundle\Repository\PostCommentRepository")
*/
class PostComment extends Comment
{
/**
* #ORM\ManyToOne(targetEntity="AppBundle\Entity\Post", inversedBy="comments")
* #ORM\JoinColumn(nullable=true, onDelete="SET NULL")
*/
private $post;
/**
* #ORM\OneToMany(targetEntity="AppBundle\Entity\ReplyComment", mappedBy="postComment", cascade={"remove"}, orphanRemoval=true)
* #ORM\OrderBy({"id"="DESC"})
*/
private $replyComments;
/**
* #return replyComment[] reply comments
*/
public function getReplyComments()
{
return $this->replyComments;
}
/**
* #param replyComment[] reply comments
*/
public function setReplyComments($replyComments)
{
$this->replyComments = $replyComments;
}
/**
* #return Post post
*/
public function getPost()
{
return $this->post;
}
/**
* #param Post post
*/
public function setPost($post)
{
$this->post = $post;
}
}
And finally this is the code in controller runnig logic
if ($postCommentForm->isSubmitted() && $postCommentForm->isValid())
{
/** #var PostComment $comment */
$comment = $postCommentForm->getData();
$comment->setPost($post);
$author = $this->getDoctrine()->getRepository('AppBundle:User')->findOneBy([
'email' => $comment->getAuthor()
]);
$comment->setAuthor($author);
$em = $this->getDoctrine()->getManager();
$em->persist($comment);
$em->flush();
return $this->redirectToRoute("single_post", [
'id' => $post->getId()
]);
}

Answer 1

At first your base class don't need to be abstract. Instead you have to insert this annotation above the class, so doctrine will get it:
#MappedSuperclass()
remove all other doctrine annotations from base entity, all of them belongs to the entity class.
use Doctrine\ORM\Mapping as ORM;
/**
*#MappedSuperclass()
*/
class Comment
{
and entity have all other annotations:
use Doctrine\ORM\Mapping as ORM;
/**
* #ORM\Entity(repositoryClass="AppBundle\Repository\PostCommentRepository")
* #ORM\Table(name="comment")
*/
class PostComment extends Comment
{
this should help