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修改如下：

1.D:\Server\websites\opencart\catalog\model\catalog\review.php 添加代码：

//判断用户是否购买过该商品

public function buyOrNot($product_id,$customer_id) {

   $query = $this->db->query("SELECT COUNT(*) AS total FROM " . DB_PREFIX . "order o LEFT JOIN " . DB_PREFIX . "order_product op ON (o.order_id = op.order_id) WHERE   o.order_status_id='5' AND o.customer_id = '" . (int)$this->customer->getId(). "' AND op.product_id = '" . (int)$product_id . "'");

   return $query->row['total'];

}

//判断用户用户是否评论过该商品

public function reviewOrNot($product_id,$customer_id) {

   $query = $this->db->query("SELECT COUNT(*) AS total FROM " . DB_PREFIX . "review WHERE  customer_id = '" . (int)$this->customer->getId(). "' AND product_id = '" . (int)$product_id . "'");

   return $query->row['total'];

}

2.D:\Server\websites\opencart\catalog\controller\product\product.php  修改代码：

$data['review_guest'] = $this->config->get('config_review_guest');

$data['review_notice'] = $this->config->get('config_review_notice');

$data['review_notice2'] = $this->config->get('config_review_notice2');

//获取满足购买过该商品的条件的数目

$review_judge=$this->model_catalog_review->buyOrNot((int)$product_id, (int)$this->customer->getId());

//获取用户评论商品的数目

$review_quantity=$this->model_catalog_review->reviewOrNot((int)$product_id, (int)$this->customer->getId());

//判断用户是否符合评论的条件，并给出提示

  if(!$this->customer->isLogged()){

   $data['review_login'] = true;

}

if($this->config->get('config_review_guest') &&$this->customer->isLogged()&&$review_judge>0){

   if($review_quantity==0){

   $data['review_guest'] = true;

}

else {

   $data['review_guest'] = false;

}

if($review_quantity>0){

   $data['review_notice2'] = true;

}

else {

   $data['review_notice2'] = false;

}

}

else {

   $data['review_guest'] = false;

}

if($review_judge==0){

   $data['review_notice'] = true;

}

else {

   $data['review_notice'] =false;

}

3.D:\Server\websites\opencart\catalog\language\english\product\product.php  添加蓝色代码：

$_['text_notice']             ='温馨提示：购买商品并完成交易后，才能评论！';

$_['text_notice2']             ='温馨提示：您已经评论过该商品，感谢您的评价！';

4.D:\Server\websites\opencart\vqmod\vqcache\vq2-catalog_view_theme_default_template_product_product.tpl  添加蓝色代码：

  <?php if ($review_status) { ?>

            <div class="tab-pane" id="tab-review">

              <form class="form-horizontal">

                <div id="review"></div>

                <h2><?php echo $text_write; ?></h2>

                <?php  if ($review_login) { ?>

                  <?php echo $text_login; echo "</br>"?>

                <?php } ?>

                 <?php  if ($review_notice) { ?>

                  <?php echo $text_notice; echo "</br>";?>

                <?php } else { ?>

                <?php echo "";?>

                   <?php } ?>

                <?php  if ($review_notice2) { ?>

                  <?php echo $text_notice2; echo "</br>";?>

                <?php } else { ?>

                <?php echo "</br>";?>

                   <?php } ?>

                <?php  if ($review_guest) { ?>

                <div class="form-group required">

                  <div class="col-sm-12">

                    <label class="control-label" for="input-name"><?php echo $entry_name; ?></label>

                    <input type="text" name="name" value="" id="input-name" class="form-control" /> </div></div>

                <div class="form-group required">

                  <div class="col-sm-12">

                    <label class="control-label" for="input-review"><?php echo $entry_review; ?></label>

                    <textarea name="text" rows="5" id="input-review" class="form-control"></textarea>

                    <div class="help-block"><?php echo $text_note; ?></div></div></div>

                <div class="form-group required">

                  <div class="col-sm-12">

                    <label class="control-label"><?php echo $entry_rating; ?></label>

                    &nbsp;&nbsp;&nbsp; <?php echo $entry_bad; ?>&nbsp;

                    <input type="radio" name="rating" value="1" />

                    &nbsp;

                    <input type="radio" name="rating" value="2" />

                    &nbsp;

                    <input type="radio" name="rating" value="3" />

                    &nbsp;

                    <input type="radio" name="rating" value="4" />

                    &nbsp;

                    <input type="radio" name="rating" value="5" />

                    &nbsp;<?php echo $entry_good; ?></div></div>

                <?php if ($site_key) { ?>

                  <div class="form-group">

                    <div class="col-sm-12">

                      <div class="g-recaptcha" data-sitekey="<?php echo $site_key; ?>"></div></div> </div>

                <?php } ?>

                <div class="buttons clearfix">

                  <div class="pull-right">

                    <button type="button" id="button-review" data-loading-text="<?php echo $text_loading; ?>" class="btn btn-primary"><?php echo $button_continue; ?></button></div> </div> 

<?php } else { ?><?php  echo "</br>";?><?php } ?> 

</form>

修改到这里，基本就可以实现用户登陆后后且买了该商品后才能购买商品，而且只能评论一次。这里还发现一个问题就是：页面刷新后才能限制评论次数。