problem understanding relation mapping in doctrine 2

Question

I read official documentation and tons of threads but still do not find solution for my situation. My case is very basic. I have 2 entities: comments and keywords for them. One comment can have many keywords but each keyword is only for one comment. Keywords are not unique in keyword table. So i decided this is one-to-many relation. Tables structure are simply like follows:

keywords

id          int(11)
comment_id  int(11)
text        varchar(30)

comments

id      int(11)
text    text

here is how i mapped them:

/**
 *  @Entity
 *  @Table(name="comments")
 **/
class Comments
{
    /** @Id @Column(type="integer") */
    private $id;
    /** @Column(type="text") */
    private $text;

    /**
     * @OneToMany(targetEntity="keywords", mappedBy="comment_id")
     */
    private $keywords;

    public function getText(){return $this->text;}
    public function getId(){return $this->id;}
    public function getKeywords(){return $this->keywords;}
}
/**
 *  @Entity
 *  @Table(name="keywords")
 */

class Keywords
{
    /** @Id @Column(type="integer") */
    private $id;

    private $text;

    public function getText(){return $this->text;}
    public function getId(){return $this->id;}
}

and how using it is like this:

$comments = $this->em->getRepository('comments' )->findAll();
foreach($comments as $comment){
    foreach($comment->getKeywords() as $keyword){
        $keyword->getText();
    }
}

and got this errors:

Notice: Undefined index: comment_id in C:\web_includes\doctrine\ORM\Persisters\BasicEntityPersister.php on line 1096
Notice: Trying to get property of non-object in C:\web_includes\doctrine\ORM\Persisters\BasicEntityPersister.php on line 1098
Warning: Invalid argument supplied for foreach() in C:\web_includes\doctrine\ORM\Persisters\BasicEntityPersister.php on line 1098
Notice: Undefined index: comment_id in C:\web_includes\doctrine\ORM\PersistentCollection.php on line 168
Fatal error: Call to a member function setValue() on a non-object in C:\web_includes\doctrine\ORM\PersistentCollection.php on line 169

What is wrong? where is should define comment_id? Is my mapping correct? i really stuck and need help so please, any advice are very welcome.

Answer 1

The mappedBy attribute does say nothing about the name of the foreign key, That is what the "@JoinColumn" annotation is for. The correct mapping for this scenario would be:

/**
 *  @Entity
 *  @Table(name="comments")
 **/
class Comments
{
    /** @Id @Column(type="integer") */
    private $id;
    /** @Column(type="text") */
    private $text;

    /**
     * @OneToMany(targetEntity="keywords", mappedBy="comment")
     */
    private $keywords;

    public function getText(){return $this->text;}
    public function getId(){return $this->id;}
    public function getKeywords(){return $this->keywords;}
}

/**
 *  @Entity
 *  @Table(name="keywords")
 */
class Keywords
{
    /** @Id @Column(type="integer") */
    private $id;

    /**
     * @ManyToOne(targetEntity="Comments", inversedBy="keywords")
     */
    private $comment;

    /**
     * @Column(type="text") */
    private $text;

    public function getText(){return $this->text;}
    public function getId(){return $this->id;}
}

Using Schema Tool it generates the SQL which equals your schema:

CREATE TABLE comments (id INT NOT NULL, text LONGTEXT NOT NULL, PRIMARY KEY(id)) ENGINE = InnoDB;
CREATE TABLE keywords (id INT NOT NULL, comment_id INT DEFAULT NULL, text LONGTEXT NOT NULL, PRIMARY KEY(id)) ENGINE = InnoDB;
ALTER TABLE keywords ADD FOREIGN KEY (comment_id) REFERENCES comments(id);

Two problems in your mapping:

1. You have to understand the difference between owning and inverse side. Just having a One-To-Many uni-directional relation requires a third join table. However with a bi-directional relation like in my mapping with the owning side property Keyword::$comment it works.
2. "mappedBy" refers to the property on the other targetEntity that is "the other side of this associations". InversedBy has somewhat the same meaning, just that inversedBy is always specified on the owning side, mappedBy on the inverse side.

This all sounds very complicated, but its a very efficient way from the ORMs technical perspective, because it allows to update associations with the least number of required SQL UPDATE statements. See the docs on how Inverse/Owning works:

http://www.doctrine-project.org/projects/orm/2.0/docs/reference/association-mapping/en#owning-side-and-inverse-side