namespace SomeBundleEntity;

use DoctrineORMMapping as ORM;
use DoctrineCommonCollectionsArrayCollection as ArrayCollection;

/**
* @ORMEntity(repositoryClass="SomeBundleEntityRepositoryPostRepository")
* @ORMTable(name="Posts")
*/
class Post {
    /**
    * @ORMId()
    * @ORMColumn(name="ID", type="integer")
    * @ORMGeneratedValue(strategy="AUTO")
    */
    protected $ID;

    /**
    * @ORMColumn(name="Title", type="string", length=255, nullable=true)
    */
    protected $Title;

    /**
    * @ORMColumn(name="Text", type="text", nullable=true)
    */
    protected $Text;

    /**
    * @ORMColumn(name="Picture", type="string", length=100, nullable=true)
    */
    protected $Picture;

    public function __toString() {
        return $this->Title;
    }

    public function getID() {
        return $this->ID;
    }

    public function getTitle() {
        return $this->Title;
    }

    public function setTitle($title) {
        $this->Title = $title;

        return $this;
    }

    public function getText() {
        return $this->Text;
    }

    public function setText($text) {
        $this->Text = $text;

        return $this;
    }

    public function getPicture() {
        return $this->Picture;
    }

    public function setPicture($picture) {
        $this->Picture= $picture;

        return $this;
    }
}

public function editAction($ID, Request $request) {
    $em = $this->getDoctrine()->getManager();

    $entity = $em->getRepository("SomeBundle:Post")->find($ID);

    if (!$entity)
        throw $this->createNotFoundException("Unable to find post.");

    $form = $this->createEditForm($entity);
    $form->handleRequest($request);
    $this->validateData($form, $entity);

    if ($form->isValid()) {
        $entity->setTitle('Title');
        $entity->setPicture('somefilepath');
        $em->flush();
    }
    ...
}

UPDATE Posts SET Title = ? WHERE ID = ?