如何在学说2中按模型检索数据

Question

我的实体是：

<?php

namespace model\base;

use Doctrine\ORM\Mapping as ORM;

/**
 * CategoryRelationship
 */
class CategoryRelationship
{
    /**
     * @var integer
     */
    private $id;

    /**
     * @var \model\base\Product
     */
    private $product;

    /**
     * @var \model\base\Category
     */
    private $category;


    /**
     * Get id
     *
     * @return integer 
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Set product
     *
     * @param \model\base\Product $product
     * @return CategoryRelationship
     */
    public function setProduct(\model\base\Product $product = null)
    {
        $this->product = $product;

        return $this;
    }

    /**
     * Get product
     *
     * @return \model\base\Product 
     */
    public function getProduct()
    {
        return $this->product;
    }

    /**
     * Set category
     *
     * @param \model\base\Category $category
     * @return CategoryRelationship
     */
    public function setCategory(\model\base\Category $category = null)
    {
        $this->category = $category;

        return $this;
    }

    /**
     * Get category
     *
     * @return \model\base\Category 
     */
    public function getCategory()
    {
        return $this->category;
    }
}

表示法是：

<?php

use Doctrine\ORM\Mapping\ClassMetadataInfo;

$metadata->setInheritanceType(ClassMetadataInfo::INHERITANCE_TYPE_NONE);
$metadata->setPrimaryTable(array(
   'name' => 'category_relationship',
   'indexes' => 
   array(
   'category_id' => 
   array(
    'columns' => 
    array(
    0 => 'category_id',
    ),
   ),
   'product_id' => 
   array(
    'columns' => 
    array(
    0 => 'product_id',
    ),
   ),
   ),
  ));
$metadata->setChangeTrackingPolicy(ClassMetadataInfo::CHANGETRACKING_DEFERRED_IMPLICIT);
$metadata->mapField(array(
   'fieldName' => 'id',
   'columnName' => '_id',
   'type' => 'integer',
   'nullable' => false,
   'unsigned' => false,
   'id' => true,
  ));
$metadata->setIdGeneratorType(ClassMetadataInfo::GENERATOR_TYPE_IDENTITY);
$metadata->mapOneToOne(array(
   'fieldName' => 'product',
   'targetEntity' => 'Product',
   'cascade' => 
   array(
   ),
   'mappedBy' => NULL,
   'inversedBy' => NULL,
   'joinColumns' => 
   array(
   0 => 
   array(
    'name' => 'product_id',
    'referencedColumnName' => 'product_id',
   ),
   ),
   'orphanRemoval' => false,
  ));
$metadata->mapOneToOne(array(
   'fieldName' => 'category',
   'targetEntity' => 'Category',
   'cascade' => 
   array(
   ),
   'mappedBy' => NULL,
   'inversedBy' => NULL,
   'joinColumns' => 
   array(
   0 => 
   array(
    'name' => 'category_id',
    'referencedColumnName' => 'category_id',
   ),
   ),
   'orphanRemoval' => false,
  ));

如何按类别检索数据？ 基本上我想更新CategoryRelationship但首先我需要通过product_id检索一个对象。