Symfony Media bundle - “Impossible to invoke a method (”id“) on a null variable.”

Question

Environment

Symfony 3.4.4 + FOSBundleUser + Sonata Admin + Media Bundle

Subject

I have installed Media Bundle. I have configured it following the steps indicated in the Official documentation.

I have created a field in my entity Products to attach a catalog in PDF format.

I have added in Sonata Adminel field mapping.

When viewing the list of products in Sonata Admin, there is no problem, but when enter to edit or create a new product, give this error:

Impossible to invoke a method ("id") on a null variable.

This is the definition of my field to attach a PDF in my entity

/**
 * @var Media
 *
 * @ORM\ManyToOne(targetEntity="Application\Sonata\MediaBundle\Entity\Media")
 * @ORM\JoinColumns({
 *     @ORM\JoinColumn(name="fileCatalog_id", referencedColumnName="id")
 * })
 */
private $fileCatalog;

This is the mapping of the field in the Sonata Admin form

->add('fileCatalog', 'sonata_type_model_list', array(
                    'required' => false,
                    'label'=>'Imagen Español'
                ), array(
                        'link_parameters' => array(
                            'context' => 'default',
                            'provider' => 'sonata.media.provider.file',
                            'empty_on_new' => true,
                        )
                    )
                )

Answer 1

I had the same issue, but in my case, my project is for a multi language site therefore each entities having its supporting Translation entities (using Knp\\DoctrineBehaviors), so what I did was.. I keep the media mapping (ORM) on both site as for example assume Product and ProductTranslation,

namespace Website\ProductBundle\Entity;

use Knp\DoctrineBehaviors\Model as ORMBehaviors;

class Product implements TranslatableInterface
{

     use ORMBehaviors\Translatable\Translatable;

     ......
     ......

     /**
      * @var Media
      *
      * @ORM\ManyToOne(targetEntity="Application\Sonata\MediaBundle\Entity\Media",  cascade={"persist"}, fetch="LAZY")
      * @ORM\JoinColumn(referencedColumnName="id", onDelete="SET NULL", nullable=true)
      */
      protected $image;
}

---

namespace Website\ProductBundle\Entity;

use Knp\DoctrineBehaviors\Model as ORMBehaviors;

class ProductTranslation
{

     use ORMBehaviors\Translatable\Translation;

     ......
     ......

     /**
      * @var Media
      *
      * @ORM\ManyToOne(targetEntity="Application\Sonata\MediaBundle\Entity\Media",  cascade={"persist"}, fetch="LAZY")
      * @ORM\JoinColumn(referencedColumnName="id", onDelete="SET NULL", nullable=true)
      */
      protected $image;
}

And thats all I was able to rid off the problem. and it works fine.

Answer 2

In my case I had missed importing ORM into the Media entity class.

use Doctrine\ORM\Mapping as ORM;

This was all it took to fix.