在以下位置找不到目标实体

我正在使用Symfony 2.3，并且在尝试列出项目时遇到此异常：

The target-entity Weber\ProjectBundle\Entity\SurveyUrl cannot be found in 'Weber\ProjectBundle\Entity\Project#surveyUrls'.

我的实体的简化为：

Project.php：

<?php

namespace Weber\ProjectBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;


/**
 * Project
 *
 * @ORM\Entity
 */
class Project
{
    /**
     * @var integer
     *
     * @ORM\Id
     * @ORM\Column(name="id", type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

    /**
     * @ORM\OneToMany(targetEntity="Respondent", mappedBy="project")
     */
    protected $respondents;

    /**
     * @ORM\OneToMany(targetEntity="SurveyUrl", mappedBy="project")
     */
    protected $surveyUrls;

    /**
     * Constructor
     */
    public function __construct()
    {
        $this->respondents = new ArrayCollection();
        $this->surveyUrls = new ArrayCollection();
    }

    /**
     * Add respondents
     *
     * @param \Weber\ProjectBundle\Entity\Respondent $respondents
     * @return Project
     */
    public function addRespondent(\Weber\ProjectBundle\Entity\Respondent $respondents)
    {
        $this->respondents[] = $respondents;

        return $this;
    }

    /**
     * Remove respondents
     *
     * @param \Weber\ProjectBundle\Entity\Respondent $respondents
     */
    public function removeRespondent(\Weber\ProjectBundle\Entity\Respondent $respondents)
    {
        $this->respondents->removeElement($respondents);
    }

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

    /**
     * Add surveyUrls
     *
     * @param \Weber\ProjectBundle\Entity\SurveyUrl $surveyUrls
     * @return Project
     */
    public function addSurveyUrl(\Weber\ProjectBundle\Entity\SurveyUrl $surveyUrls)
    {
        $this->surveyUrls[] = $surveyUrls;

        return $this;
    }

    /**
     * Remove surveyUrls
     *
     * @param \Weber\ProjectBundle\Entity\SurveyUrl $surveyUrls
     */
    public function removeSurveyUrl(\Weber\ProjectBundle\Entity\SurveyUrl $surveyUrls)
    {
        $this->surveyUrls->removeElement($surveyUrls);
    }

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

Respondent.php：

<?php

namespace Weber\ProjectBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * Respondent
 *
 * @ORM\Entity
 */
class Respondent
{
    /**
     * @var integer
     *
     * @ORM\Id
     * @ORM\Column(name="id", type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\ManyToOne(targetEntity="Project")
     */
    protected $project;

    /**
     * Set project
     *
     * @param \Weber\ProjectBundle\Entity\Project $project
     * @return Respondent
     */
    public function setProject(\Weber\ProjectBundle\Entity\Project $project = null)
    {
        $this->project = $project;

        return $this;
    }

    /**
     * Get project
     *
     * @return \Weber\ProjectBundle\Entity\Project 
     */
    public function getProject()
    {
        return $this->project;
    }
}

和SurveyUrl.php：

<?php

namespace Weber\ProjectBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * SurveyURL
 *
 * @ORM\Entity
 */
class SurveyURL
{
    /**
     * @var integer
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * The project for this url.
     *
     * @ORM\ManyToOne(targetEntity="Project", inversedBy="surveyUrls")
     * (I have also tried without 'inversedBy')
     */
    protected $project;

    /**
     * May be null.
     * The respondent that answered this survey.
     *
     * @ORM\OneToOne(targetEntity="Respondent")
     */
    protected $respondent;

    /**
     * Set project
     *
     * @param \Weber\ProjectBundle\Entity\Project $project
     * @return SurveyURL
     */
    public function setProject(\Weber\ProjectBundle\Entity\Project $project = null)
    {
        $this->project = $project;

        return $this;
    }

    /**
     * Get project
     *
     * @return \Weber\ProjectBundle\Entity\Project 
     */
    public function getProject()
    {
        return $this->project;
    }

    /**
     * Set respondent
     *
     * @param \Weber\ProjectBundle\Entity\Respondent $respondent
     * @return SurveyURL
     */
    public function setRespondent(\Weber\ProjectBundle\Entity\Respondent $respondent = null)
    {
        $this->respondent = $respondent;

        return $this;
    }

    /**
     * Get respondent
     *
     * @return \Weber\ProjectBundle\Entity\Respondent 
     */
    public function getRespondent()
    {
        return $this->respondent;
    }
}

我不明白的是，在创建SurveyUrl实体之前，根本没有问题，而且两个实体的配置几乎相同。

谢谢你的帮助。