Error sonata classificiation bundle - php

Question

I have a problem. I installed sonata classification bundle.
But when I want to create a new post I have an error:
Neither the property "collection" nor one of the methods "getCollection()", "collection()", "isCollection()", "hasCollection()", "__get()" exist and have public access in class "DN\SiteBundle\Entity\Post".*
This is my code in PostAdmin.php (src/DN/SiteBundle/Admin/PostAdmin.php)
namespace DN\SiteBundle\Admin;
use Sonata\AdminBundle\Admin\Admin;
use Sonata\AdminBundle\Form\FormMapper;
use Sonata\AdminBundle\Datagrid\DatagridMapper;
use Sonata\AdminBundle\Datagrid\ListMapper;
use Sonata\AdminBundle\Show\ShowMapper;
use Sonata\CoreBundle\Validator\ErrorElement;
use Knp\Menu\ItemInterface as MenuItemInterface;
class PostAdmin extends Admin
{
// Fields to be shown on create/edit forms
protected function configureFormFields(FormMapper $formMapper)
{
$formMapper
->add('title', 'text', array('label' => 'Post Title'))
->add('content')
->add('publication')
->add('author')
->add('collection', 'sonata_type_model_list', array('required' => false));
}
//...
}
?>
This is my code in Post.php (src/DN/SiteBundle/Entity/Post.php)
namespace DN\SiteBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
use Gedmo\Mapping\Annotation as Gedmo;
use DoctrineExtensions\Taggable\Taggable;
use Doctrine\Common\Collections\ArrayCollection;
/**
* #ORM\Entity
*/
class Post implements Taggable
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var string
*
* #ORM\Column(name="title", type="string", length=255)
*/
private $title;
/**
* #var string
*
* #ORM\Column(name="author", type="string", length=255)
*/
private $author;
/**
* #var string
*
* #ORM\Column(name="content", type="text")
*/
private $content;
/**
* #var \DateTime
*
* #ORM\Column(name="created_at", type="datetime")
*/
private $created_at;
/**
* #var boolean
*
* #ORM\Column(name="publication", type="boolean")
*/
private $publication;
/**
* #var string
* #Gedmo\Slug(fields={"title"})
* #ORM\Column(name="slug", type="string", length=255)
*/
private $slug;
private $tags;
public function getTags()
{
$this->tags = $this->tags ?: new ArrayCollection();
return $this->tags;
}
public function getTaggableType()
{
return 'DN_tag';
}
public function getTaggableId()
{
return $this->getId();
}
/**
* Get id
*
* #return integer
*/
public function getId()
{
return $this->id;
}
/**
* Set title
*
* #param string $title
* #return Post
*/
public function setTitle($title)
{
$this->title = $title;
return $this;
}
/**
* Get title
*
* #return string
*/
public function getTitle()
{
return $this->title;
}
/**
* Set author
*
* #param string $author
* #return Post
*/
public function setAuthor($author)
{
$this->author = $author;
return $this;
}
/**
* Get author
*
* #return string
*/
public function getAuthor()
{
return $this->author;
}
/**
* Set content
*
* #param string $content
* #return Post
*/
public function setContent($content)
{
$this->content = $content;
return $this;
}
/**
* Get content
*
* #return string
*/
public function getContent()
{
return $this->content;
}
/**
* Set publication
*
* #param boolean $publication
* #return Post
*/
public function setPublication($publication)
{
$this->publication = $publication;
return $this;
}
/**
* Get publication
*
* #return boolean
*/
public function getPublication()
{
return $this->publication;
}
/**
* Set slug
*
* #param string $slug
* #return Post
*/
public function setSlug($slug)
{
$this->slug = $slug;
return $this;
}
/**
* Get slug
*
* #return string
*/
public function getSlug()
{
return $this->slug;
}
/**
* Set created_at
*
* #param \DateTime $createdAt
* #return Post
*/
public function setCreatedAt($createdAt)
{
$this->created_at = $createdAt;
return $this;
}
/**
* Get created_at
*
* #return \DateTime
*/
public function getCreatedAt()
{
return $this->created_at;
}
public function __construct()
{
$this->created_at = new \DateTime("now");
}
public function __toString()
{
return $this->getTitle();
}
}

Answer 1

The name of your field should be "tags" instead of "collection" I guess.
I don't see a property "collection" in your Entity.
The first parameter of the add method should be the name of your property defined in your Entity.
namespace DN\SiteBundle\Admin;
use Sonata\AdminBundle\Admin\Admin;
use Sonata\AdminBundle\Form\FormMapper;
use Sonata\AdminBundle\Datagrid\DatagridMapper;
use Sonata\AdminBundle\Datagrid\ListMapper;
use Sonata\AdminBundle\Show\ShowMapper;
use Sonata\CoreBundle\Validator\ErrorElement;
use Knp\Menu\ItemInterface as MenuItemInterface;
class PostAdmin extends Admin
{
// Fields to be shown on create/edit forms
protected function configureFormFields(FormMapper $formMapper)
{
$formMapper
->add('title', 'text', array('label' => 'Post Title'))
->add('content')
->add('publication')
->add('author')
->add('collection', 'sonata_type_model_list', array('required' => false));
}
//...
}
?>
Documentation on forms : https://sonata-project.org/bundles/doctrine-orm-admin/master/doc/reference/form_field_definition.html