EventAdmin.php

<?php

namespace MyBundle\Admin;

use Sonata\AdminBundle\Admin\Admin;
use Sonata\AdminBundle\Datagrid\ListMapper;
use Sonata\AdminBundle\Datagrid\DatagridMapper;
use Sonata\AdminBundle\Form\FormMapper;
use Sonata\AdminBundle\Show\ShowMapper;
use FOS\UserBundle\Model\UserManagerInterface;
use Sonata\AdminBundle\Route\RouteCollection;
use Symfony\Component\HttpFoundation\File\UploadedFile;

class EventAdmin extends Admin
{

    /**
     * {@inheritdoc}
     */
    protected function configureShowFields(ShowMapper $showMapper)
    {
        $showMapper
            ->add('name')
            ->add('location');
    }

    /**
     * {@inheritdoc}
     */
    protected function configureFormFields(FormMapper $formMapper)
    {

        $formMapper
            ->add('name')
            ->add('location')
            ->add('logo', 'file', array('label' => 'Image file', 'required' => false));
    }

    /**
     * {@inheritdoc}
     */
    protected function configureDatagridFilters(DatagridMapper $filterMapper)
    {
        $filterMapper
            ->add('onStage')
            ->add('name')
            ->add('location');
    }

    /**
     * {@inheritdoc}
     */
    protected function configureListFields(ListMapper $listMapper)
    {
        $listMapper
            ->addIdentifier('onStage')
            ->addIdentifier('name')
            ->addIdentifier('location');
    }

    public function prePersist($event)
    {
        $this->saveFile($event);
    }

    public function preUpdate($event)
    {
        $this->saveFile($event);
    }

    public function saveFile($event)
    {
        $basepath = $this->getRequest()->getBasePath();
        $event->upload($basepath);
    }

}