使用symfony2中的manytomany关联删除

Question

我有两个实体：工具和操作系统。两者都有联系。每个工具都可以在许多OS中运行。所以我通过多种关系将它们联系起来。 我可以添加一个工具并将其关联到许多操作系统，但我不知道如何删除工具及其与Oss的关系（这些关系被添加到我的数据库中的os_tool表中）。

工具实体：

use Lang\LanguageBundle\Form\ToolType;
namespace Lang\LanguageBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
 * Tool
 */
class Tool
{
    /**
     * @var integer
     */
    private $id;
    /**
     * @var string
     */
    private $nombre;
     /**
     * @var \Doctrine\Common\Collections\Collection
     */
    private $oss;
     /**
     * Constructor
     */
    public function __construct()
    {
        $this->oss = new \Doctrine\Common\Collections\ArrayCollection();
    }

    /**
     * Add os
     *
     * @param \Lang\LanguageBundle\Entity\OS $os
     * @return Tool
     */
    public function addOs(\Lang\LanguageBundle\Entity\OS $os)
    {
        $os->addTool($this);
        $this->oss[] = $os;
    }

    /**
     * Remove os
     *
     * @param \Lang\LanguageBundle\Entity\OS $os
     */
    public function removeOs(\Lang\LanguageBundle\Entity\OS $oss)
    {

        $this->oss->removeElement($oss);
    }

    /**
     * Get oss
     *
     * @return \Doctrine\Common\Collections\Collection 
     */
    public function getOss()
    {
        return $this->oss;
    }    
}

OS实体：

namespace Lang\LanguageBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
 * OS
 */
class OS
{
    /**
     * @var integer
     */
    private $id;
    /**
     * @var string
     */
    private $osName;
    /**
     * @var \Doctrine\Common\Collections\Collection
     */
    private $tools;
    /**
     * Constructor
     */
    public function __construct()
    {
        $this->tools = new \Doctrine\Common\Collections\ArrayCollection();
    }
    /**
     * Add tool
     *
     * @param \Lang\LanguageBundle\Entity\Tool $tool
     * @return OS
     */
    public function addTool(\Lang\LanguageBundle\Entity\Tool $tool)
    {
        $this->tools[] = $tool;
        return $this;
    }

    /**
     * Remove tools
     *
     * @param \Lang\LanguageBundle\Entity\Tool $tools
     */
    public function removeTool(\Lang\LanguageBundle\Entity\Tool $tools)
    {
        $this->tools->removeElement($tools);
    }

    /**
     * Get tools
     *
     * @return \Doctrine\Common\Collections\ArrayCollection 
     */
    public function getTools()
    {
        return $this->tools;
    }
}

工具控制器：

public function deleteAction(Request $request, $id)
{
    $form = $this->createDeleteForm($id);
    $form->handleRequest($request);

    if ($form->isValid()) {
        $em = $this->getDoctrine()->getManager();
        $entity = $em->getRepository('LangLanguageBundle:Tool')->find($id);

        if (!$entity) {
            throw $this->createNotFoundException('Unable to find Tool entity.');
        }
        //$em->remove($entity);
        //$em->flush();
    }
    return $this->redirect($this->generateUrl('tool'));
}
private function createDeleteForm($id)
{
    return $this->createFormBuilder()
        ->setAction($this->generateUrl('tool_delete', array('id' => $id)))
        ->setMethod('DELETE')
        ->add('submit', 'submit', array('label' => 'Delete'))
        ->getForm()
    ;
}

在Tool.orm.yml中我有以下代码：

manyToMany:
    oss:
        targetEntity: OS
        mappedBy: tools
        cascade: [ remove, persist ]

在OS.orm.yml中我有以下代码：

manyToMany:
    tools:
        targetEntity: Tool
        inversedBy: oss
        JoinTable:
            name: tool_os
        joinColumns:
            JoinColumn:
                name: os_id
                referencedColumnName: id
        inverseJoinColumns:
            JoinColumn:
                name: tool_id  
                referencedColumnName: id